Co-reporter:Qian Wang, Hong Yan Zhao, Po-Kam Lo, William W. Y. Lam, Kai-Chung Lau, and Tai-Chu Lau
Inorganic Chemistry November 6, 2017 Volume 56(Issue 21) pp:12699-12699
Publication Date(Web):October 13, 2017
DOI:10.1021/acs.inorgchem.7b02509
We have previously reported that the oxidation of SO32– to SO42– by a trans-dioxoruthenium(VI) complex, [RuVI(TMC)(O)2)]2+ (RuVI; TMC = 1,4,8,11-tetramethyl-1,4,8,11-tetraazcyclotetradecane) in aqueous solutions occurs via an O-atom transfer mechanism. In this work, we have reinvestigated the effects of the pH on the oxidation of SIV by RuVI in more detail in order to obtain kinetic data for the HSO3– pathway. The HSO3– pathway exhibits a deuterium isotope effect of 17.4, which indicates that O–H bond breaking occurs in the rate-limiting step. Density functional theory calculations have been performed that suggest that the oxidation of HSO3– by RuVI may occur via a concerted or stepwise proton-coupled O-atom transfer mechanism.
Co-reporter:Cai Li;Kwok-Wa Ip;Wai-Lun Man;Dan Song;Ming-Liang He;Shek-Man Yiu;Guangyu Zhu
Chemical Science (2010-Present) 2017 vol. 8(Issue 10) pp:6865-6870
Publication Date(Web):2017/09/25
DOI:10.1039/C7SC02205K
Two novel series of (salen)ruthenium(III) complexes bearing guanidine and amidine axial ligands were synthesized, characterized, and evaluated for anticancer activity. In vitro cytotoxicity tests demonstrate that these complexes are cytotoxic against various cancer cell lines and the leading complexes have remarkable cancer-cell selectivity. A detailed study of the guanidine complex 7 and the amidine complex 13 reveals two distinguished modes of action. Complex 7 weakly binds to DNA and induces DNA damage, cell cycle arrest, and typical apoptosis pathways in MCF-7 cells. In contrast, complex 13 induces paraptosis-like cell death hallmarked by massive vacuole formation, mitochondrial swelling, and ER stress, resulting in significant cytotoxicity against human breast cancer cells. Our results provide an extraordinary example of tuning the mechanism of action of (salen)ruthenium(III) anticancer complexes by modifying the structure of the axial ligands.
Co-reporter:Jing Xiang, Qian Wang, Shek-Man Yiu, and Tai-Chu Lau
Inorganic Chemistry 2017 Volume 56(Issue 4) pp:
Publication Date(Web):January 31, 2017
DOI:10.1021/acs.inorgchem.6b02645
The guanidine moiety of arginine is involved in the active sites of a variety of enzymes, such as nitric oxide synthase (NOS) and NiFe hydrogenase. In this paper we aim to investigate the effects of a metal center on the oxidation of guanidine, which should provide an interesting comparison with the biological aerobic oxidation of arginine catalyzed by NOS. We studied the oxidation of an osmium(III) guanidine complex, mer-[Os(L){N(H)C(NH2)2}(CN)3]−, (OsG, HL = 2-(2-hydroxyphenyl)benzoxazole) by m-chloroperbenzoic acid (m-CPBA), which is potentially an O atom transfer reagent, and by (NH4)2[CeIV(NO3)6], which is a one-electron oxidant. With m-CPBA, mer-[Os(NO)(L)(CN)3]− (mer-OsNO) is the product, while with CeIV, mer-[OsVI(N)(L)(CN)3]− (mer-OsN) is formed instead. The crystal structures of mer-OsNO and mer-OsN were determined by X-ray crystallography. The mechanisms for the oxidation of OsG by m-CPBA and CeIV are proposed.
Co-reporter:Dr. Hoi-Ki Kwong;Dr. Po-Kam Lo;Dr. Shek-Man Yiu;Dr. Hajime Hirao;Dr. Kai-Chung Lau; Tai-Chu Lau
Angewandte Chemie 2017 Volume 129(Issue 40) pp:12428-12431
Publication Date(Web):2017/09/25
DOI:10.1002/ange.201705986
AbstractThe OsVI nitrido complex, OsVI(N)(quin)2(OTs) (1, quin=2-quinaldinate, OTs=tosylate), is a highly selective and efficient catalyst for the ring hydroxylation of alkylbenzenes with H2O2 at room temperature. Oxidation of various alkylbenzenes occurs with ring/chain oxidation ratios ranging from 96.7/3.3 to 99.9/0.1, and total product yields from 93 % to 98 %. Moreover, turnover numbers up to 6360, 5670, and 3880 can be achieved for the oxidation of p-xylene, ethylbenzene, and mesitylene, respectively. Density functional theory calculations suggest that the active intermediate is an OsVIII nitrido oxo species.
Co-reporter:Dr. Hoi-Ki Kwong;Dr. Po-Kam Lo;Dr. Shek-Man Yiu;Dr. Hajime Hirao;Dr. Kai-Chung Lau; Tai-Chu Lau
Angewandte Chemie International Edition 2017 Volume 56(Issue 40) pp:12260-12263
Publication Date(Web):2017/09/25
DOI:10.1002/anie.201705986
AbstractThe OsVI nitrido complex, OsVI(N)(quin)2(OTs) (1, quin=2-quinaldinate, OTs=tosylate), is a highly selective and efficient catalyst for the ring hydroxylation of alkylbenzenes with H2O2 at room temperature. Oxidation of various alkylbenzenes occurs with ring/chain oxidation ratios ranging from 96.7/3.3 to 99.9/0.1, and total product yields from 93 % to 98 %. Moreover, turnover numbers up to 6360, 5670, and 3880 can be achieved for the oxidation of p-xylene, ethylbenzene, and mesitylene, respectively. Density functional theory calculations suggest that the active intermediate is an OsVIII nitrido oxo species.
Co-reporter:Zhenguo Guo; Siwei Cheng; Claudio Cometto; Elodie Anxolabéhère-Mallart; Siu-Mui Ng; Chi-Chiu Ko; Guijian Liu; Lingjing Chen; Marc Robert
Journal of the American Chemical Society 2016 Volume 138(Issue 30) pp:9413-9416
Publication Date(Web):July 21, 2016
DOI:10.1021/jacs.6b06002
The design of highly efficient and selective photocatalytic systems for CO2 reduction that are based on nonexpensive materials is a great challenge for chemists. The photocatalytic reduction of CO2 by [Co(qpy)(OH2)2]2+ (1) (qpy = 2,2′:6′,2″:6″,2‴-quaterpyridine) and [Fe(qpy)(OH2)2]2+ (2) have been investigated. With Ru(bpy)32+ as the photosensitizer and 1,3-dimethyl-2-phenyl-2,3-dihydro-1H-benzo[d]imidazole as the sacrificial reductant in CH3CN/triethanolamine solution under visible-light excitation (blue light-emitting diode), a turnover number (TON) for CO as high as 2660 with 98% selectivity can be achieved for the cobalt catalyst. In the case of the iron catalyst, the TON was >3000 with up to 95% selectivity. More significantly, when Ru(bpy)32+ was replaced by the organic dye sensitizer purpurin, TONs of 790 and 1365 were achieved in N,N-dimethylformamide for the cobalt and iron catalysts, respectively.
Co-reporter:Jianhui Xie; Wai-Lun Man; Chun-Yuen Wong; Xiaoyong Chang; Chi-Ming Che
Journal of the American Chemical Society 2016 Volume 138(Issue 18) pp:5817-5820
Publication Date(Web):April 25, 2016
DOI:10.1021/jacs.6b02923
Proton-coupled electron-transfer reactions of phenols have received considerable attention because of their fundamental interest and their relevance to many biological processes. Here we describe a remarkable four-electron oxidation of phenols by a (salen)ruthenium(VI) complex in the presence of pyridine in CH3OH to afford (salen)ruthenium(II) p-benzoquinone imine complexes. Mechanistic studies indicate that this reaction occurs in two phases. The first phase is proposed to be a two-electron transfer process that involves electrophilic attack by Ru≡N at the phenol aromatic ring, followed by proton shift to generate a Ru(IV) p-hydroxyanilido intermediate. In the second phase the intermediate undergoes intramolecular two-electron transfer, followed by rapid deprotonation to give the Ru(II) p-benzoquinone imine product.
Co-reporter:Gui Chen, Lingjing Chen, Li Ma, Hoi-Ki Kwong and Tai-Chu Lau
Chemical Communications 2016 vol. 52(Issue 59) pp:9271-9274
Publication Date(Web):22 Jun 2016
DOI:10.1039/C6CC04173F
Mn(V) nitrido complex [Mn(N)(CN)4]2− is an efficient catalyst for visible-light induced oxidation of alkenes and alcohols in water using [Ru(bpy)3]2+ as a photosensitizer and [Co(NH3)5Cl]2+ as a sacrificial oxidant. Alkenes are oxidized to epoxides and alcohols to carbonyl compounds.
Co-reporter:Jing Xiang, Qian Wang, Shek-Man Yiu, Wai-Lun Man, Hoi-Ki Kwong, and Tai-Chu Lau
Inorganic Chemistry 2016 Volume 55(Issue 10) pp:5056
Publication Date(Web):May 2, 2016
DOI:10.1021/acs.inorgchem.6b00652
The aerobic oxidation of the N-hydroxyguanidinum moiety of N-hydroxyarginine to NO is a key step in the biosynthesis of NO by the enzyme nitric oxide synthase (NOS). So far, there is no chemical system that can efficiently carry out similar aerobic oxidation to give NO. We report here the synthesis and X-ray crystal structure of an osmium(III) N-hydroxyguanidine complex, mer-[OsIII{NH═C(NH2)(NHOH)}(L)(CN)3]− (OsGOH, HL = 2-(2-hydroxyphenyl)benzoxazole), which to the best of our knowledge is the first example of a transition metal N-hydroxyguanidine complex. More significantly, this complex readily undergoes aerobic oxidation at ambient conditions to generate NO. The oxidation is pH-dependent; at pH 6.8, fac-[Os(NO)(L)(CN)3]− is formed in which the NO produced is bound to the osmium center. On the other hand, at pH 12, aerobic oxidation of OsGOH results in the formation of the ureato complex [OsIII(NHCONH2)(L)(CN)3]2– and free NO. Mechanisms for this aerobic oxidation at different pH values are proposed.
Co-reporter:Jianhui Xie, Li Ma, William W. Y. Lam, Kai-Chung Lau and Tai-Chu Lau
Dalton Transactions 2016 vol. 45(Issue 1) pp:70-73
Publication Date(Web):13 Nov 2015
DOI:10.1039/C5DT04303D
The oxidation of phenols by HFeO4− proceeds via a hydrogen atom transfer (HAT) mechanism, as evidenced by a large deuterium isotope effect and a linear correlation between the log(rate constant) and bond dissociation free energy (BDFE) of phenols. The Marcus cross relation has been applied to predict the rate constant of HAT from hydroquinone to HFeO4−.
Co-reporter:Yingying Liu;Dr. Siu-Mui Ng;Dr. William W. Y. Lam;Dr. Shek-Man Yiu ; Tai-Chu Lau
Angewandte Chemie International Edition 2016 Volume 55( Issue 1) pp:288-291
Publication Date(Web):
DOI:10.1002/anie.201507933
Abstract
Seven-coordinate ruthenium oxo species have been proposed as active intermediates in catalytic water oxidation by a number of highly active ruthenium catalysts, however such species have yet to be isolated. Reported herein is the first example of a seven-coordinate group 8 metal-oxo species, [OsV(O)(qpy)(pic)Cl]2+ (qpy=2,2′:6′,2′′:6′′,2′′′-quaterpyridine, pic=4-picoline). The X-ray crystal structure of this complex shows that it has a distorted pentagonal bipyramidal geometry with an OsO distance of 1.7375 Å. This oxo species undergoes facile O-atom and H-atom-transfer reactions with various organic substrates. Notably it can abstract H atoms from alkylaromatics with CH bond dissociation energy as high as 90 kcal mol−1. This work suggests that highly active oxidants may be designed based on group 8 seven-coordinate metal oxo species.
Co-reporter:Yingying Liu;Dr. Siu-Mui Ng;Dr. William W. Y. Lam;Dr. Shek-Man Yiu ; Tai-Chu Lau
Angewandte Chemie 2016 Volume 128( Issue 1) pp:296-299
Publication Date(Web):
DOI:10.1002/ange.201507933
Abstract
Seven-coordinate ruthenium oxo species have been proposed as active intermediates in catalytic water oxidation by a number of highly active ruthenium catalysts, however such species have yet to be isolated. Reported herein is the first example of a seven-coordinate group 8 metal-oxo species, [OsV(O)(qpy)(pic)Cl]2+ (qpy=2,2′:6′,2′′:6′′,2′′′-quaterpyridine, pic=4-picoline). The X-ray crystal structure of this complex shows that it has a distorted pentagonal bipyramidal geometry with an OsO distance of 1.7375 Å. This oxo species undergoes facile O-atom and H-atom-transfer reactions with various organic substrates. Notably it can abstract H atoms from alkylaromatics with CH bond dissociation energy as high as 90 kcal mol−1. This work suggests that highly active oxidants may be designed based on group 8 seven-coordinate metal oxo species.
Co-reporter:Lingjing Chen; Zhenguo Guo; Xi-Guang Wei; Charlotte Gallenkamp; Julien Bonin; Elodie Anxolabéhère-Mallart; Kai-Chung Lau; Tai-Chu Lau;Marc Robert
Journal of the American Chemical Society 2015 Volume 137(Issue 34) pp:10918-10921
Publication Date(Web):August 12, 2015
DOI:10.1021/jacs.5b06535
Molecular catalysis of carbon dioxide reduction using earth-abundant metal complexes as catalysts is a key challenge related to the production of useful products—the “solar fuels”—in which solar energy would be stored. A direct approach using sunlight energy as well as an indirect approach where sunlight is first converted into electricity could be used. A CoII complex and a FeIII complex, both bearing the same pentadentate N5 ligand (2,13-dimethyl-3,6,9,12,18-pentaazabicyclo[12.3.1]octadeca-1(18),2,12,14,16-pentaene), were synthesized, and their catalytic activity toward CO2 reduction was investigated. Carbon monoxide was formed with the cobalt complex, while formic acid was obtained with the iron-based catalyst, thus showing that the catalysis product can be switched by changing the metal center. Selective CO2 reduction occurs under electrochemical conditions as well as photochemical conditions when using a photosensitizer under visible light excitation (λ > 460 nm, solvent acetonitrile) with the Co catalyst. In the case of the Fe catalyst, selective HCOOH production occurs at low overpotential. Sustained catalytic activity over long periods of time and high turnover numbers were observed in both cases. A catalytic mechanism is suggested on the basis of experimental results and preliminary quantum chemistry calculations.
Co-reporter:Lingjing Chen, Gui Chen, Chi-Fai Leung, Shek-Man Yiu, Chi-Chiu Ko, Elodie Anxolabéhère-Mallart, Marc Robert, and Tai-Chu Lau
ACS Catalysis 2015 Volume 5(Issue 1) pp:356
Publication Date(Web):December 1, 2014
DOI:10.1021/cs501534h
A series of nickel(II) complexes bearing tetradentate macrocyclic N4, N3S, and N3P ligands were synthesized, and their photocatalytic activity toward proton reduction has been investigated by using [Ir(dF(CF3)ppy)2(dmbpy)]PF6 (dF(CF3)ppy = 2-(2,4-difluorophenyl)-5-trifluoromethylpyridine and dmbpy = 4,4′-dimethyl-2,2′-dipyridyl) as the photosensitizer and triethylamine (TEA) as the sacrificial reductant. The complex [Ni(L4)]2+ (L4 = 2,12-dimethyl-7-phenyl-3,11,17-triaza-7-phospha-bicyclo[11,3,1]heptadeca-1(17),13,15-triene), which bears a phosphorus donor atom, shows the highest efficiency with TON up to 5000 under optimized conditions, while the tetraaza macrocyclic nickel complexes [Ni(L1)]2+ and [Ni(L2)]2+ (L1 = 2,12-dimethyl-3,7,11,17-tetra-azabicyclo[11.3.l]heptadeca-1(17),2,11,13,15-pentaene; L2 = 2,12-dimethyl-3,7,11,17-tetra-azabicyclo[11.3.l]heptadeca-1(17),13,15-triene) show lower photocatalytic activities. Transient UV–vis absorption and spectroelectrochemical experiments show that Ni(II) is reduced to Ni(I) under photocatalytic conditions. However, dynamic light scattering and mercury poisoning experiments suggest that the Ni(I) is further reduced to Ni(0) nanoparticles which are the real catalysts for H2 production. Electrocatalytic proton reduction by [Ni(L4)]2+ has also been investigated. In this case, the electrochemical behavior is consistent with a homogeneous pathway, and no Ni nanoparticles were observed on the electrode surface during the first few hours of electrolysis. However, on prolonged electrolysis for >17 h, nickel-based nanoparticles were observed on the electrode surface, which are active catalysts for H2 production.Keywords: electrochemical catalysis; hydrogen evolution; macrocyclic ligands; nickel catalyst; photocatalysis
Co-reporter:Man Chen, Yi Pan, Hoi-Ki Kwong, Raymond J. Zeng, Kai-Chung Lau and Tai-Chu Lau
Chemical Communications 2015 vol. 51(Issue 71) pp:13686-13689
Publication Date(Web):20 Jul 2015
DOI:10.1039/C5CC03636D
The osmium(VI) nitrido complex, [OsVI(N)(L)(CH3OH)]+ (1, L = N,N′-bis(salicylidene)-o-cyclohexyldiamine dianion) is an efficient catalyst for the oxidation of alkanes under ambient conditions using H2O2 as the oxidant. Alkanes are oxidized to the corresponding alcohols and ketones, with yields up to 75% and turnover numbers up to 2230. Experimental and computational studies are consistent with a mechanism that involves O-atom transfer from H2O2 to [OsVI(N)(L)]+ to generate an [OsVIII(N)(O)(L)]+ active intermediate.
Co-reporter:Peng Tan, Hoi-Ki Kwong and Tai-Chu Lau
Chemical Communications 2015 vol. 51(Issue 61) pp:12189-12192
Publication Date(Web):16 Jun 2015
DOI:10.1039/C5CC02868J
An iron(III) complex bearing a cross-bridged cyclam ligand (4,11-dimethyl-1,4,8,11-tetraazabicyclo[6.6.2]hexadecane) is an efficient catalyst for the oxidation of both water and alcohols using sodium periodate as the oxidant. In catalytic water oxidation a maximum turnover number (TON) of 1030 is achieved, while in catalytic alcohol oxidation >95% conversions and yields can be obtained.
Co-reporter:Quanjun Xiang, Gui Chen and Tai-Chu Lau
RSC Advances 2015 vol. 5(Issue 64) pp:52210-52216
Publication Date(Web):03 Jun 2015
DOI:10.1039/C5RA09354F
Shape and facet engineering of crystals at the nanoscale level has become an important strategy for optimizing the reactivity of catalysts in heterogeneous catalysis. We report here the fabrication of four morphology-controlled α-Fe2O3 catalysts with exposed specific facets by a solvothermal method. The effects of morphology and exposed facets of these α-Fe2O3 nanocrystals towards visible light-driven water oxidation have been investigated. Water oxidation was carried out using two catalytic systems, Fe2O3/[Ru(bpy)3]2+/S2O82− and Fe2O3/AgNO3, at λ > 420 nm. The α-Fe2O3 nanocubes with exposed {012} facets exhibit much higher catalytic activity than α-Fe2O3 nanoflakes with {001} facets. This work demonstrates that the catalytic activity of α-Fe2O3 nanocrystals in photocatalytic water oxidation is morphology-dependent and the reactivity trend can be rationalized in terms of exposed facets in the order of {012} > {001}. This study provides a new approach to the design of highly effective water oxidation catalysts by engineering the morphology and the exposed facets of crystals.
Co-reporter:Jing Xiang;Li-Hui Jia;Hui-Sheng Wang;Shie-Ming Peng;Song Gao
European Journal of Inorganic Chemistry 2015 Volume 2015( Issue 6) pp:1065-1073
Publication Date(Web):
DOI:10.1002/ejic.201402959
Abstract
The synthesis, crystal structures, and magnetic properties of three cyano-bridged heterodimetallic compounds prepared from the paramagnetic RuIII building block mer-[RuIII(CN-sap)(CN)3]2– (1) are described. Complex 1 reacts with [MnII(LN5)(Cl)(H2O)]Cl and [MnII(bipy)2(Cl)2] (bipy = bipyridine) to produce the 1D zigzag chain {[RuIII(CN-sap)(CN)](μ-CN)2[MnII(LN5)]·3MeOH}n {2; LN5 = 2,13-dimethyl-3,6,9,12,18-pentaazabicyclo[12.3.1]octadeca-1(18),2,12,14,16-pentaene, CN-sapH2 = 2-hydroxy-N-(2-hydroxyphenyl)benzimidoyl cyanide} and the octanuclear compound {[RuIII(CN-sap)(CN)](μ-CN)2[MnII(bipy)(MeOH)][RuIII(CN-sap)](μ-CN)3[MnII(bipy)2]}2·8MeOH (3), respectively. The MnII centers have a pentagonal-bipyramidal environment in 2 and a distorted octahedral environment in 3. Complex 1 reacts with [NiII(cyclen)(Cl)2] (cyclen = 1,4,7,10-tetraazacyclododecane) in MeOH to produce the molecular square {[RuIII(CN-sap)(CN)](μ-CN)2[NiII(cyclen)]}2·8MeOH (4). Compounds 2 and 3 exhibit antiferromagnetic coupling between the RuIII and MnII centers, whereas 4 exhibits ferromagnetic coupling between the RuIII and NiII centers through the cyano bridges.
Co-reporter:Li Ma;Qian Wang;Dr. Wai-Lun Man;Dr. Hoi-Ki Kwong;Dr. Chi-Chiu Ko ; Tai-Chu Lau
Angewandte Chemie 2015 Volume 127( Issue 17) pp:5335-5338
Publication Date(Web):
DOI:10.1002/ange.201500507
Abstract
The study of manganese complexes as water-oxidation catalysts (WOCs) is of great interest because they can serve as models for the oxygen-evolving complex of photosystem II. In most of the reported Mn-based WOCs, manganese exists in the oxidation states III or IV, and the catalysts generally give low turnovers, especially with one-electron oxidants such as CeIV. Now, a different class of Mn-based catalysts, namely manganese(V)–nitrido complexes, were explored. The complex [MnV(N)(CN)4]2− turned out to be an active homogeneous WOC using (NH4)2[Ce(NO3)6] as the terminal oxidant, with a turnover number of higher than 180 and a maximum turnover frequency of 6 min−1. The study suggests that active WOCs may be constructed based on the MnV(N) platform.
Co-reporter:Li Ma;Qian Wang;Dr. Wai-Lun Man;Dr. Hoi-Ki Kwong;Dr. Chi-Chiu Ko ; Tai-Chu Lau
Angewandte Chemie International Edition 2015 Volume 54( Issue 17) pp:5246-5249
Publication Date(Web):
DOI:10.1002/anie.201500507
Abstract
The study of manganese complexes as water-oxidation catalysts (WOCs) is of great interest because they can serve as models for the oxygen-evolving complex of photosystem II. In most of the reported Mn-based WOCs, manganese exists in the oxidation states III or IV, and the catalysts generally give low turnovers, especially with one-electron oxidants such as CeIV. Now, a different class of Mn-based catalysts, namely manganese(V)–nitrido complexes, were explored. The complex [MnV(N)(CN)4]2− turned out to be an active homogeneous WOC using (NH4)2[Ce(NO3)6] as the terminal oxidant, with a turnover number of higher than 180 and a maximum turnover frequency of 6 min−1. The study suggests that active WOCs may be constructed based on the MnV(N) platform.
Co-reporter:Wai-Lun Man, William W. Y. Lam, and Tai-Chu Lau
Accounts of Chemical Research 2014 Volume 47(Issue 2) pp:427
Publication Date(Web):September 18, 2013
DOI:10.1021/ar400147y
Nitrido complexes (M≡N) may be key intermediates in chemical and biological nitrogen fixation and serve as useful reagents for nitrogenation of organic compounds. Osmium(VI) nitrido complexes bearing 2,2′:6′,2″-terpyridine (terpy), 2,2′-bipyridine (bpy), or hydrotris(1-pyrazolyl)borate anion (Tp) ligands are highly electrophilic: they can react with a variety of nucleophiles to generate novel osmium(IV)/(V) complexes.This Account describes our recent results studying the reactivity of nitridocomplexes of ruthenium(VI), osmium(VI), and manganese(V) that bear Schiff bases and other simple anionic ligands. We demonstrate that these nitrido complexes exhibit rich chemical reactivity. They react with various nucleophiles, activate C–H bonds, undergo N···N coupling, catalyze the oxidation of organic compounds, and show anticancer activities. Ruthenium(VI) nitrido complexes bearing Schiff base ligands, such as [RuVI(N)(salchda)(CH3OH)]+ (salchda = N,N′-bis(salicylidene)o-cyclohexyldiamine dianion), are highly electrophilic. This complex reacts readily at ambient conditions with a variety of nucleophiles at rates that are much faster than similar reactions using OsVI≡N. This complex also carries out unique reactions, including the direct aziridination of alkenes, C–H bond activation of alkanes and C–N bond cleavage of anilines. The addition of ligands such as pyridine can enhance the reactivity of [RuVI(N)(salchda)(CH3OH)]+. Therefore researchers can tune the reactivity of Ru≡N by adding a ligand L trans to nitride: L–Ru≡N. Moreover, the addition of various nucleophiles (Nu) to RuVI≡N initially generate the ruthenium(IV) imido species RuIV–N(Nu), a new class of hydrogen-atom transfer (HAT) reagents.Nucleophiles also readily add to coordinated Schiff base ligands in OsVI≡N and RuVI≡N complexes. These additions are often stereospecific, suggesting that the nitrido ligand has a directing effect on the incoming nucleophile. M≡N is also a potential platform for the design of new oxidation catalysts. For example, [OsVI(N)Cl4]− catalyzes the oxidation of alkanes by a variety of oxidants, and the addition of Lewis acids greatly accelerates these reactions. [MnV(N)(CN)4]2– is another highly efficient oxidation catalyst, which facilitates the epoxidation of alkenes and the oxidation of alcohols to carbonyl compounds using H2O2. Finally, M≡N can potentially bind to and exert various effects on biomolecules. For example, a number of OsVI≡N complexes exhibit novel anticancer properties, which may be related to their ability to bind to DNA or other biomolecules.
Co-reporter:Li Ma ; Yi Pan ; Wai-Lun Man ; Hoi-Ki Kwong ; William W. Y. Lam ; Gui Chen ; Kai-Chung Lau
Journal of the American Chemical Society 2014 Volume 136(Issue 21) pp:7680-7687
Publication Date(Web):May 5, 2014
DOI:10.1021/ja5019546
The oxidation of various alkanes catalyzed by [MnV(N)(CN)4]2– using various terminal oxidants at room temperature has been investigated. Excellent yields of alcohols and ketones (>95%) are obtained using H2O2 as oxidant and CF3CH2OH as solvent. Good yields (>80%) are also obtained using (NH4)2[Ce(NO3)6] in CF3CH2OH/H2O. Kinetic isotope effects (KIEs) are determined by using an equimolar mixture of cyclohexane (c-C6H12) and cyclohexane-d12 (c-C6D12) as substrate. The KIEs are 3.1 ± 0.3 and 3.6 ± 0.2 for oxidation by H2O2 and Ce(IV), respectively. On the other hand, the rate constants for the formation of products using c-C6H12 or c-C6D12 as single substrate are the same. These results are consistent with initial rate-limiting formation of an active intermediate between [Mn(N)(CN)4]2– and H2O2 or CeIV, followed by H-atom abstraction from cyclohexane by the active intermediate. When PhCH2C(CH3)2OOH (MPPH) is used as oxidant for the oxidation of c-C6H12, the major products are c-C6H11OH, c-C6H10O, and PhCH2C(CH3)2OH (MPPOH), suggesting heterolytic cleavage of MPPH to generate a Mn═O intermediate. In the reaction of H2O2 with [Mn(N)(CN)4]2– in CF3CH2OH, a peak at m/z 628.1 was observed in the electrospray ionization mass spectrometry, which is assigned to the solvated manganese nitrido oxo species, (PPh4)[Mn(N)(O)(CN)4]−·CF3CH2OH. On the basis of the experimental results the proposed mechanism for catalytic alkane oxidation by [MnV(N)(CN)4]2–/ROOH involves initial rate-limiting O-atom transfer from ROOH to [Mn(N)(CN)4]2– to generate a manganese(VII) nitrido oxo active species, [MnVII(N)(O)(CN)4]2–, which then oxidizes alkanes (R′H) via a H-atom abstraction/O-rebound mechanism. The proposed mechanism is also supported by density functional theory calculations.
Co-reporter:Qian Wang, Wai-Lun Man, William W. Y. Lam and Tai-Chu Lau
Chemical Communications 2014 vol. 50(Issue 99) pp:15799-15802
Publication Date(Web):05 Nov 2014
DOI:10.1039/C4CC07568D
The oxidation of ascorbic acid (H2A) by [RuVI(N)(L)(MeOH)]+ in aqueous acidic solutions has the following stoichiometry: 2[RuVI(N)] + 3H2A → 2[RuIII(NH2–HA)]+ + A. Mechanisms involving HAT/N-rebound at low pH (≤2) and nucleophilic attack at the nitride at high pH (≥5) are proposed.
Co-reporter:Man Chen, Siu-Mui Ng, Shek-Man Yiu, Kai-Chung Lau, Raymond J. Zeng and Tai-Chu Lau
Chemical Communications 2014 vol. 50(Issue 95) pp:14956-14959
Publication Date(Web):10 Oct 2014
DOI:10.1039/C4CC07607A
A double-helical dicobalt(II) complex [Co2(spy)2](ClO4)4 (spy = 2,2′:6′,2″:6″,2‴:6‴,2⁗:6⁗,2⁗′-sexipyridine) (1) is found to catalyze visible light-induced water oxidation by [Ru(bpy)3]2+/Na2S2O8, with a maximum turnover number of 442. Several lines of evidence suggest that 1 functions as a molecular catalyst and does not produce any CoOx in water oxidation.
Co-reporter:Dr. Gui Chen;Lingjing Chen;Dr. Siu-Mui Ng ; Tai-Chu Lau
ChemSusChem 2014 Volume 7( Issue 1) pp:127-134
Publication Date(Web):
DOI:10.1002/cssc.201300561
Abstract
Chemical and visible-light-driven water oxidation catalyzed by a number of Ni complexes and salts have been investigated at pH 7–9 in borate buffer. For chemical oxidation, [Ru(bpy)3]3+ (bpy=2,2′-bipyridine) was used as the oxidant, with turnover numbers (TONs) >65 and a maximum turnover frequency (TOFmax) >0.9 s−1. Notably, simple Ni salts such as Ni(NO3)2 are more active than Ni complexes that bear multidentate N-donor ligands. The Ni complexes and salts are also active catalysts for visible-light-driven water oxidation that uses [Ru(bpy)3]2+ as the photosensitizer and S2O82− as the sacrificial oxidant; a TON>1200 was obtained at pH 8.5 by using Ni(NO3)2 as the catalyst. Dynamic light scattering measurements revealed the formation of nanoparticles in chemical and visible-light-driven water oxidation by the Ni catalysts. These nanoparticles aggregated during water oxidation to form submicron particles that were isolated and shown to be partially reduced β-NiOOH by various techniques, which include SEM, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, XRD, and IR spectroscopy. These results suggest that the Ni complexes and salts act as precatalysts that decompose under oxidative conditions to form an active nickel oxide catalyst. The nature of this active oxide catalyst is discussed.
Co-reporter:Yingying Liu;Dr. Siu-Mui Ng;Dr. Shek-Man Yiu;Dr. William W. Y. Lam;Xi-Guang Wei;Dr. Kai-Chung Lau; Tai-Chu Lau
Angewandte Chemie 2014 Volume 126( Issue 52) pp:14696-14699
Publication Date(Web):
DOI:10.1002/ange.201408795
Abstract
Polypyridyl and related ligands have been widely used for the development of water oxidation catalysts. Supposedly these ligands are oxidation-resistant and can stabilize high-oxidation-state intermediates. In this work a series of ruthenium(II) complexes [Ru(qpy)(L)2]2+ (qpy=2,2′:6′,2′′:6′′,2′′′-quaterpyridine; L=substituted pyridine) have been synthesized and found to catalyze CeIV-driven water oxidation, with turnover numbers of up to 2100. However, these ruthenium complexes are found to function only as precatalysts; first, they have to be oxidized to the qpy-N,N′′′-dioxide (ONNO) complexes [Ru(ONNO)(L)2]3+ which are the real catalysts for water oxidation.
Co-reporter:Dr. Wai-Lun Man;Jianhui Xie;Po-Kam Lo;Dr. William W. Y. Lam;Dr. Shek-Man Yiu;Dr. Kai-Chung Lau ; Tai-Chu Lau
Angewandte Chemie International Edition 2014 Volume 53( Issue 32) pp:8463-8466
Publication Date(Web):
DOI:10.1002/anie.201404421
Abstract
Exploring new reactivity of metal nitrides is of great interest because it can give insights to N2 fixation chemistry and provide new methods for nitrogenation of organic substrates. In this work, reaction of a (salen)ruthenium(VI) nitrido complex with various alkynes results in the formation of novel (salen)ruthenium(III) imine complexes. Kinetic and computational studies suggest that the reactions go through an initial ruthenium(IV) aziro intermediate, followed by addition of nucleophiles to give the (salen)ruthenium(III) imine complexes. These unprecedented reactions provide a new pathway for nitrogenation of alkynes based on a metal nitride.
Co-reporter:Yingying Liu;Dr. Siu-Mui Ng;Dr. Shek-Man Yiu;Dr. William W. Y. Lam;Xi-Guang Wei;Dr. Kai-Chung Lau; Tai-Chu Lau
Angewandte Chemie International Edition 2014 Volume 53( Issue 52) pp:14468-14471
Publication Date(Web):
DOI:10.1002/anie.201408795
Abstract
Polypyridyl and related ligands have been widely used for the development of water oxidation catalysts. Supposedly these ligands are oxidation-resistant and can stabilize high-oxidation-state intermediates. In this work a series of ruthenium(II) complexes [Ru(qpy)(L)2]2+ (qpy=2,2′:6′,2′′:6′′,2′′′-quaterpyridine; L=substituted pyridine) have been synthesized and found to catalyze CeIV-driven water oxidation, with turnover numbers of up to 2100. However, these ruthenium complexes are found to function only as precatalysts; first, they have to be oxidized to the qpy-N,N′′′-dioxide (ONNO) complexes [Ru(ONNO)(L)2]3+ which are the real catalysts for water oxidation.
Co-reporter:Dr. Wai-Lun Man;Jianhui Xie;Po-Kam Lo;Dr. William W. Y. Lam;Dr. Shek-Man Yiu;Dr. Kai-Chung Lau ; Tai-Chu Lau
Angewandte Chemie 2014 Volume 126( Issue 32) pp:8603-8606
Publication Date(Web):
DOI:10.1002/ange.201404421
Abstract
Exploring new reactivity of metal nitrides is of great interest because it can give insights to N2 fixation chemistry and provide new methods for nitrogenation of organic substrates. In this work, reaction of a (salen)ruthenium(VI) nitrido complex with various alkynes results in the formation of novel (salen)ruthenium(III) imine complexes. Kinetic and computational studies suggest that the reactions go through an initial ruthenium(IV) aziro intermediate, followed by addition of nucleophiles to give the (salen)ruthenium(III) imine complexes. These unprecedented reactions provide a new pathway for nitrogenation of alkynes based on a metal nitride.
Co-reporter:Wai-Lun Man ; Jianhui Xie ; Yi Pan ; William W. Y. Lam ; Hoi-Ki Kwong ; Kwok-Wa Ip ; Shek-Man Yiu ; Kai-Chung Lau
Journal of the American Chemical Society 2013 Volume 135(Issue 15) pp:5533-5536
Publication Date(Web):March 28, 2013
DOI:10.1021/ja401553d
We report experimental and computational studies of the facile oxidative C–N bond cleavage of anilines by a (salen)ruthenium(VI) nitrido complex. We provide evidence that the initial step involves nucleophilic attack of aniline at the nitrido ligand of the ruthenium complex, which is followed by proton and electron transfer to afford a (salen)ruthenium(II) diazonium intermediate. This intermediate then undergoes unimolecular decomposition to generate benzene and N2.
Co-reporter:Quan Tang, Wen-Xiu Ni, Chi-Fai Leung, Wai-Lun Man, Kenneth King-Kwan Lau, Yimin Liang, Yun-Wah Lam, Wai-Yeung Wong, Shie-Ming Peng, Gui-Jian Liu and Tai-Chu Lau
Chemical Communications 2013 vol. 49(Issue 85) pp:9980-9982
Publication Date(Web):28 Aug 2013
DOI:10.1039/C3CC42250J
A series of osmium(VI) nitrido complexes supported by quinolinolato ligands have been prepared and they exhibit promising in vitro anti-cancer activities. These results establish that OsVIN is a potentially versatile and promising platform for the design of a variety of high-valent anti-cancer drugs.
Co-reporter:Jing Xiang, Li-Hui Jia, Bing-Wu Wang, Shek-Man Yiu, Shie-Ming Peng, Wai-Yeung Wong, Song Gao and Tai-Chu Lau
Dalton Transactions 2013 vol. 42(Issue 11) pp:3876-3887
Publication Date(Web):16 Jan 2013
DOI:10.1039/C2DT32331A
The synthesis, crystal structures and magnetic properties of six cyano-bridged heterobimetallic compounds prepared from a paramagnetic RuIII building block, trans-(PPh4)[RuIII(Q)2(CN)2] (1) (Q = the anion of 8-hydroxyquinoline), are described. 1 reacts with hydrated MnCl2 in MeOH or DMF to produce a trinuclear compound {[RuIII(Q)2(CN)2]2[MnII(MeOH)4]}·8MeOH (2), or a 1-D zigzag chain {[MnII(DMF)2(Cl)](μ-CN)2[RuIII(Q)2]}n(3). The MnII has a distorted octahedral environment in 2 and a trigonal-bipyramidal environment in 3. 1 reacts with [MnIII(L1)(Cl)(H2O)] in MeOH to produce the 1-D {[RuIII(Q)2](μ-CN)2[MnIII(L1)]}n (4) that consists of alternating MnIII and RuIII units. 1 also reacts with [CuII(cyclam)Br2] and [NiII(cyclam)Cl2] in MeOH to produce the trinuclear complexes [RuIII(Q)2(CN2)]2[MII(cyclam)] (M = CuII (5) and NiII (6)). On the other hand, the reaction of 1 with [NiII(cyclen)Cl2] produces a 1-D zigzag chain {([RuIII(Q)2(CN2)][NiII(cyclen)])[RuIII(Q)2(CN2)]}n (7). Compounds 2–4 exhibit antiferromagnetic coupling between RuIII and MnIII/II centres. Antiferromagnetic coupling also occurs between RuIII and CuII centres in 5. On the other hand, compounds 6 and 7 exhibit ferromagnetic coupling between RuIII and NiII through cyanide bridges.
Co-reporter:Zongmin Hu, Li Ma, Jianhui Xie, Hongxia Du, William W. Y. Lam and Tai-Chu Lau
New Journal of Chemistry 2013 vol. 37(Issue 6) pp:1707-1710
Publication Date(Web):19 Apr 2013
DOI:10.1039/C3NJ00102D
The polypyridylruthenium(II) complex, cis-[Ru(2,9-Me2phen)2(OH2)2]2+, is a highly efficient catalyst for the oxidation of alcohols to carbonyl products in water using sodium bromate (NaBrO3) as the terminal oxidant. Excellent conversions and yields are readily achieved at room temperature.
Co-reporter:Dr. Gui Chen;Lingjing Chen;Dr. Siu-Mui Ng;Dr. Wai-Lun Man ; Tai-Chu Lau
Angewandte Chemie 2013 Volume 125( Issue 6) pp:1833-1835
Publication Date(Web):
DOI:10.1002/ange.201209116
Co-reporter:Dr. Gui Chen;Lingjing Chen;Dr. Siu-Mui Ng;Dr. Wai-Lun Man ; Tai-Chu Lau
Angewandte Chemie International Edition 2013 Volume 52( Issue 6) pp:1789-1791
Publication Date(Web):
DOI:10.1002/anie.201209116
Co-reporter:Chi-Fai Leung, Siu-Mui Ng, Chi-Chiu Ko, Wai-Lun Man, Jiashou Wu, Lingjing Chen and Tai-Chu Lau
Energy & Environmental Science 2012 vol. 5(Issue 7) pp:7903-7907
Publication Date(Web):17 May 2012
DOI:10.1039/C2EE21840B
The complex [CoII(qpy)(OH2)2]2+ (qpy = 2,2′:6′,2′′:6′′,2′′′-quaterpyridine) is an efficient visible light-driven catalyst for both water oxidation and reduction. It catalyses photochemical oxygen evolution from water at pH 8.0 with [RuII(bpy)3]2+/S2O82− (λ = 457 nm, max TON = 335, bpy = 2,2′-bipyridine). It also catalyses photochemical hydrogen generation from [IrIII(dF(CF3)ppy)2(dtbbpy)]+/TEOA (dF(CF3)ppy = anion of 2-(2,4-difluorophenyl)-5-trifluoromethylpyridine, dtbbpy = 4,4′-di-tert-butyl-2,2′-bipyridine, TEOA = triethanolamine) in aqueous acetonitrile (λ > 420 nm, max TON = 1730).
Co-reporter:Wen-Xiu Ni, Wai-Lun Man, Shek-Man Yiu, Man Ho, Myra Ting-Wai Cheung, Chi-Chiu Ko, Chi-Ming Che, Yun-Wah Lam and Tai-Chu Lau
Chemical Science 2012 vol. 3(Issue 5) pp:1582-1588
Publication Date(Web):03 Feb 2012
DOI:10.1039/C2SC01031C
Eight new nitridoosmium(VI) complexes with the general formula [OsVI(N)Cl3(Hazole)2] have been synthesized and characterized. The cellular uptake and the antiproliferative activities of these compounds against a panel of human cancer cell lines have been investigated. Complexes with pyrazole derivatives (1, 2, 3 and 4) are found to possess significant in vitro cytotoxicity. Further studies of compounds 1 and 3 indicate that they induce S phase arrest in HeLa cells followed by apoptosis, possibly as a result of binding with DNA.
Co-reporter:Zongmin Hu, Hongxia Du, Wai-Lun Man, Chi-Fai Leung, Haojun Liang and Tai-Chu Lau
Chemical Communications 2012 vol. 48(Issue 8) pp:1102-1104
Publication Date(Web):07 Nov 2011
DOI:10.1039/C1CC15860K
cis-[Ru(2,9-Me2phen)2(OH2)2]2+ reacts readily with chlorite at room temperature at pH 4.9 and 6.8. The ruthenium(II) complex can catalyze the disproportionation of chlorite to chlorate and chloride, the oxidation of chlorite to chlorine dioxide, as well as the oxidation of alcohols by chlorite.
Co-reporter:Wei Liu, Bin Zheng, Sheng Cheng, Yan Fu, Wei Li, Tai-Chu Lau and Haojun Liang
Soft Matter 2012 vol. 8(Issue 26) pp:7017-7023
Publication Date(Web):30 May 2012
DOI:10.1039/C2SM25839K
The lead-induced folding into G-quadruplex structures for three guanine-rich oligonucleotides, two model human telomeric oligomers (HTG/T2) and thrombin-binding aptamer (TBA), was characterized by equilibrium titrations, rapid mixing techniques and stopped-flow kinetics. The analysis of optical titration data reveals that the saturated Pb2+–DNA binding stoichiometries are 1:1, 2:1 and 3:1 for TBA, HTG and T2, respectively. Thermal denaturation experiments were performed to determine the structural stability. The overall results are consistent with the higher stability of T2 that contains four G-quartets, as opposed to HTG and TBA that have only three and two quartets, respectively. We also present kinetic studies of the formation of G-quadruplexes of G-rich DNA induced by Pb2+ ions. The binding of Pb2+ ions to G-DNA is a complex multiple pathway process, which is affected by the sequence of the G-DNA. The studies show that the connecting loops of the DNA play an important role in modulating the structures.
Co-reporter:Jing Xiang, Li-Hui Jia, Wai-Lun Man, Kang Qian, Gene-Hsiang Lee, Shie-Ming Peng, Shek-Man Yiu, Song Gao and Tai-Chu Lau
Dalton Transactions 2012 vol. 41(Issue 19) pp:5794-5798
Publication Date(Web):13 Feb 2012
DOI:10.1039/C2DT11810F
Reaction of [RuVI(N)(sap)Cl] with excess NaN3 affords a novel paramagnetic triazidoruthenium(III) complex [RuIII(sap)(N3)3]2−, which is isolated as a PPh4+ salt (1). Reaction of 1 with Ni2+ and Co2+ ions produce two isostructural hexanuclear [Ru4M2] compounds, [RuIV4MII2(μ3-OMe)2(μ-OMe)2(μ-N)2(μ-N3)2(μ-Ophenoxy)2(sap)4 (MeOH)4] (M = Ni 2 or Co 3). The molecular structures of 1–3 have been determined by X-ray crystallography. 1 is a mononuclear ruthenium(III) compound where three azide ligands are bonded to ruthenium in a meridional fashion, while compounds 2 and 3 are isostructural hexanuclear compounds containing a defective face-sharing dicubane-like core with two missing vertexes. Variable-temperature dc magnetic susceptibility studies have been carried out for 2 and 3. These data indicate that there are four diamagnetic Ru(IV) ions in 2 and 3 and there is ferromagnetic interaction between the two Ni2+ in 2 and Co2+ in 3via the methoxy bridges.
Co-reporter:Dr. Wai-Lun Man;Dr. William W. Y. Lam;Dr. Hoi-Ki Kwong;Dr. Shek-Man Yiu ; Tai-Chu Lau
Angewandte Chemie 2012 Volume 124( Issue 36) pp:9235-9238
Publication Date(Web):
DOI:10.1002/ange.201204136
Co-reporter:Dr. Wai-Lun Man;Dr. William W.Y. Lam;Siu-Mui Ng;Wenny Y.K. Tsang ; Tai-Chu Lau
Chemistry - A European Journal 2012 Volume 18( Issue 1) pp:138-144
Publication Date(Web):
DOI:10.1002/chem.201102297
Abstract
In aqueous acidic solutions trans-[RuVI(L)(O)2]2+ (L=1,12-dimethyl-3,4:9,10-dibenzo-1,12-diaza-5,8-dioxacyclopentadecane) is rapidly reduced by excess NO to give trans-[Ru(L)(NO)(OH)]2+. When ≤1 mol equiv NO is used, the intermediate RuIV species, trans-[RuIV(L)(O)(OH2)]2+, can be detected. The reaction of [RuVI(L)(O)2]2+ with NO is first order with respect to [RuVI] and [NO], k2=(4.13±0.21)×101 M−1 s−1 at 298.0 K. ΔH≠ and ΔS≠ are (12.0±0.3) kcal mol−1 and −(11±1) cal mol−1 K−1, respectively. In CH3CN, ΔH≠ and ΔS≠ have the same values as in H2O; this suggests that the mechanism is the same in both solvents. In CH3CN, the reaction of [RuVI(L)(O)2]2+ with NO produces a blue-green species with λmax at approximately 650 nm, which is characteristic of N2O3. N2O3 is formed by coupling of NO2 with excess NO; it is relatively stable in CH3CN, but undergoes rapid hydrolysis in H2O. A mechanism that involves oxygen atom transfer from [RuVI(L)(O)2]2+ to NO to produce NO2 is proposed. The kinetics of the reaction of [RuIV(L)(O)(OH2)]2+ with NO has also been investigated. In this case, the data are consistent with initial one-electron O− transfer from RuIV to NO to produce the nitrito species [RuIII(L)(ONO)(OH2)]2+ (k2>106 M−1 s−1), followed by a reaction with another molecule of NO to give [Ru(L)(NO)(OH)]2+ and NO2− (k2=54.7 M−1 s−1).
Co-reporter:Jing Xiang, Larry Tso-Lun Lo, Chi-Fai Leung, Shek-Man Yiu, Chi-Chiu Ko, and Tai-Chu Lau
Organometallics 2012 Volume 31(Issue 20) pp:7101-7108
Publication Date(Web):October 10, 2012
DOI:10.1021/om300621x
Reaction of [RuII(PR3)3Cl2] with 2-methyl-8-quinolinolate (MeQ) in the presence of Et3N in MeOH produced the neutral carbonyl hydrido complexes [RuII(MeQ)(PR3)2(CO)(H)] (R = Ph (1), MeC6H4 (2), MeOC6H4 (3)). An analogous reaction occurs between [RuII(PPh3)3Cl2] and MeQH in ethanol to give [RuII(MeQ)(PPh3)2(CO)(CH3)] (4). The carbonyl, hydride, and methyl ligands of these complexes are most likely derived from the decarbonylation of ROH. Reaction of [RuII(PPh3)3(CO)(H)2] with 5-substituted quinolinolato ligands (XQ, X = H, Cl, Ph) produced the neutral complexes [RuII(XQ)(PPh3)2(CO)(H)] (XQ = Q (5), ClQ (6), PhQ (7)). Treatment of 1 and 5–7 with excess KCN in MeOH following by metathesis with PPh4Cl afforded PPh4+ salts of the anionic carbonyl dicyano complexes [RuII(XQ)(CO)(CN)2(PPh3)]− (XQ = MeQ (8), Q (9) ClQ (10), PhQ (11)). Under similar conditions, reaction of 1 with excess CyNC in the presence of NH4PF6 afforded [RuII(MeQ)(CyNC)2(CO)(PPh3)]+ (12). All complexes have been characterized by IR, ESI/MS, 1H NMR and elemental analysis. The crystal structures of complexes 3, 4, 8, and 12 have been determined by X-ray crystallography. The UV and emission spectra of these complexes have also been investigated. All complexes exhibit short-lived quinolinolate-based LC fluorescence in solution at room temperature and dual emissions derived from LC fluorescence and phosphorescence at 77 K glassy medium. These emissions are relatively insensitive to the nature of the ancillary ligands but are readily tunable by varying the substituents on the quinolinolato ligand.
Co-reporter:Dr. Wai-Lun Man;Dr. William W. Y. Lam;Dr. Hoi-Ki Kwong;Dr. Shek-Man Yiu ; Tai-Chu Lau
Angewandte Chemie International Edition 2012 Volume 51( Issue 36) pp:9101-9104
Publication Date(Web):
DOI:10.1002/anie.201204136
Co-reporter:Wen-Xiu Ni, Wai-Lun Man, Myra Ting-Wai Cheung, Raymond Wai-Yin Sun, Yuan-Lan Shu, Yun-Wah Lam, Chi-Ming Che and Tai-Chu Lau
Chemical Communications 2011 vol. 47(Issue 7) pp:2140-2142
Publication Date(Web):04 Jan 2011
DOI:10.1039/C0CC04515B
A nitridoosmium(VI) complex [OsVI(N)(sap)(OH2)Cl] (H2sap = N-salicylidene-2-aminophenol) displays prominent in vitro and in vivo anti-cancer properties, induces S- and G2/M-phase arrest and forms a stable adduct with dianionic 5′-guanosine monophosphate.
Co-reporter:Shek-Man Yiu, Wai-Lun Man, Xin Wang, William W. Y. Lam, Siu-Mui Ng, Hoi-Ki Kwong, Kai-Chung Lau and Tai-Chu Lau
Chemical Communications 2011 vol. 47(Issue 14) pp:4159-4161
Publication Date(Web):28 Feb 2011
DOI:10.1039/C1CC00019E
MnO4− is activated by BF3 to undergo intramolecular coupling of two oxo ligands to generate O2. DFT calculations suggest that there should be a spin intercrossing between the singlet and triplet potential energy surfaces on going from the active intermediate [MnO2(OBF3)2]− to the O⋯O coupling transition state.
Co-reporter:Hoi-Ki Kwong, Po-Kam Lo, Kai-Chung Lau and Tai-Chu Lau
Chemical Communications 2011 vol. 47(Issue 14) pp:4273-4275
Publication Date(Web):07 Mar 2011
DOI:10.1039/C0CC05487A
The manganese(V) nitrido complex (PPh4)2[Mn(N)(CN)4] is an active catalyst for alkene epoxidation and alcohol oxidation using H2O2 as an oxidant. The catalytic oxidation is greatly enhanced by the addition of just one equivalent of acetic acid. The oxidation of ethene by this system has been studied computationally by the DFT method.
Co-reporter:Hongxia Du, Po-Kam Lo, Zongmin Hu, Haojun Liang, Kai-Chung Lau, Yi-Ning Wang, William W. Y. Lam and Tai-Chu Lau
Chemical Communications 2011 vol. 47(Issue 25) pp:7143-7145
Publication Date(Web):25 May 2011
DOI:10.1039/C1CC12024G
The oxidation of alcohols by KMnO4 is greatly accelerated by various Lewis acids. Notably the rate is increased by 4 orders of magnitude in the presence of Ca2+. The mechanisms of the oxidation of CH3OH and PhCH(OH)CH3 by MnO4− and BF3·MnO4− have also been studied computationally by the DFT method.
Co-reporter:Jing Xiang, Li-Hui Jia, Wai-Lun Man, Kang Qian, Shek-Man Yiu, Gene-Hsiang Lee, Shie-Ming Peng, Song Gao and Tai-Chu Lau
Chemical Communications 2011 vol. 47(Issue 30) pp:8694-8696
Publication Date(Web):02 Jul 2011
DOI:10.1039/C1CC12446C
Reaction of [RuII(PPh3)3Cl2] with HQ and KCN produces a new dicyanoruthenium(III) building block, [RuIII(Q)2(CN)2]−. It reacts with hydrated CoCl2 in MeOH or DMF to produce a trinuclear compound 2 or a 1-D zigzag chain 3.
Co-reporter:Gui Chen, Wai-Lun Man, Shek-Man Yiu, Tsz-Wing Wong, Lap Szeto, Wing-Tak Wong and Tai-Chu Lau
Dalton Transactions 2011 vol. 40(Issue 9) pp:1938-1944
Publication Date(Web):26 Jan 2011
DOI:10.1039/C0DT01367F
The preparation of a number of binuclear (salen)osmium phosphinidine and phosphiniminato complexes using various strategies are described. Treatment of [OsVI(N)(L1)(sol)](X) (sol = H2O or MeOH) with PPh3 affords an osmium(IV) phosphinidine complex [OsIV{N(H)PPh3}(L1)(OMe)](X) (X = PF61a, ClO41b). If the reaction is carried out in CH2Cl2 in the presence of excess pyrazine the osmium(III) phosphinidine species [OsIII{N(H)PPh3}(L1)(pz)](PF6) 2 can be generated. On the other hand, if the reaction is carried out in CH2Cl2 in the presence of a small amount of H2O, a μ-oxo osmium(IV) phosphinidine complex is obtained, [(L1){PPh3N(H)}OsIV–O–OsIV{N(H)PPh3}(L1)](PF6)23. Furthermore, if the reaction of [OsVI(N)(L1)(OH2)]PF6 with PPh3 is done in the presence of 2, the μ-pyrazine species, [(L1){PPh3N(H)}OsIII–pz–OsIII{N(H)PPh3}(L1)](PF6)24 can be isolated. Novel binuclear osmium(IV) complexes can be prepared by the use of a diphosphine ligand to attack two OsVIN. Reaction of [OsVI(N)(L1)(OH2)](PF6) with PPh2–CC–PPh2 or PPh2–(CH2)3–PPh2 in MeOH affords the binuclear complexes [(MeO)(L1)OsIV{N(H)PPh2–R–PPh2N(H)}OsIV(L1)(OMe)](PF6)2 (R = CC 5, (CH2)36). Reaction of [OsVI(N)(L2)Cl] with PPh2FcPPh2 generates a novel trimetallic complex, [Cl(L2)OsIV{NPPh2–Fc–PPh2N}OsIV(L2)Cl] 7. The structures of 1b, 2, 3, 4, 5 and 7 have been determined by X-ray crystallography.
Co-reporter:Chi-Fai Leung, Yong-Zhen Chen, Han-Qing Yu, Shek-Man Yiu, Chi-Chiu Ko, Tai-Chu Lau
International Journal of Hydrogen Energy 2011 Volume 36(Issue 18) pp:11640-11645
Publication Date(Web):September 2011
DOI:10.1016/j.ijhydene.2011.06.062
The cobalt(III) macrocyclic Schiff-base complex, [CoIII(CR)Cl]ClO4 (CR = 2,12-dimethyl-3,7,11,17-tetra-azabicyclo[11.3.1]-heptadeca-1(17),2,11,13,15-pentaene), is an active catalyst for the electrocatalytic proton reduction to generate dihydrogen in both acetonitrile and 100% aqueous solution (at −0.57 and −0.85 V vs SCE, respectively), using p-cyanoanilinium tetrafluoroborate and acetic acid as proton sources, respectively. Bulk electrolysis confirmed that dihydrogen is produced with >90% Faradaic yields and >50 TON in both solvents. [CoIII(CR)Cl2]ClO4 also catalyzes photo-driven (λ > 390 nm) hydrogen production in aqueous acetonitrile at TON of 180 (not optimized), using [IrIII(ppy)2(bpy)]PF6 as the photosensitizer, triethanolamine (TEOA) as the sacrificial donor and acetic acid as the proton source.
Co-reporter:Zongmin Hu, Hongxia Du, Chi-Fai Leung, Haojun Liang, and Tai-Chu Lau
Industrial & Engineering Chemistry Research 2011 Volume 50(Issue 21) pp:12288-12292
Publication Date(Web):October 1, 2011
DOI:10.1021/ie201637r
The species cis-[RuII(2,9-Me2phen)2(OH2)2]2+, both in homogeneous solution and supported on Dowex cation-exchange resin, is a highly active and robust catalyst for the oxidation of alcohols and alkenes in water at room temperature, using Ce(IV) and IO4– as terminal oxidants, with a turnover number (TON) of >104.
Co-reporter:Dr. Jing Xiang;Dr. Wai-Lun Man;Dr. Shek-Man Yiu; Shie-Ming Peng; Tai-Chu Lau
Chemistry - A European Journal 2011 Volume 17( Issue 46) pp:13044-13051
Publication Date(Web):
DOI:10.1002/chem.201101722
Abstract
Reaction of [OsVI(N)(L1)(Cl)(OH2)] (1) with CN− under various conditions affords (PPh4)[OsVI(N)(L1)(CN)(Cl)] (2), (PPh4)2[OsVI(N)(L2)(CN)2] (3), and a novel hydrogen cyanamido complex, (PPh4)2[OsIII{N(H)CN}(L3)(CN)3] (4). Compound 4 reacts readily with both electrophiles and nucleophiles. Protonation and methylation of 4 produce (PPh4)[OsIII(NCNH2)(L3)(CN)3] (5) and (PPh4)[OsIII(NCNMe2)(L3)(CN)3] (6), respectively. Nucleophilic addition of NH3, ethylamine, and diethylamine readily occur at the C atom of the hydrogen cyanamide ligand of 4 to produce osmium guanidine complexes with the general formula [OsIII{N(H)C(NH2)NR1R2}(L3)(CN)3]−, which have been isolated as PPh4 salts (R1=R2=H (7); R1=H, R2=CH2CH3 (8); R1=R2=CH2CH3 (9)). The molecular structures of 1–5 and 7 and 8 have been determined by X-ray crystallography.
Co-reporter:Chi-Fai Leung, Shek-Man Yiu, Jing Xiang and Tai-Chu Lau
Chemical Communications 2010 vol. 46(Issue 40) pp:7575-7577
Publication Date(Web):17 Sep 2010
DOI:10.1039/C0CC01645D
Reaction of RuVIN complexes bearing 8-quinolinolato ligands with NCCH2CN/piperidine and NaTCNE afford novel ruthenium(II) dicyanoimine and diimine/imino-oxazolone complexes, respectively.
Co-reporter:Jing Xiang, Wai-Lun Man, Junfang Guo, Shek-Man Yiu, Gene-Hsiang Lee, Shie-Ming Peng, Guancheng Xu, Song Gao and Tai-Chu Lau
Chemical Communications 2010 vol. 46(Issue 33) pp:6102-6104
Publication Date(Web):26 Jul 2010
DOI:10.1039/C001732A
Reaction of excess cyanide with a ruthenium(VI) nitrido complex bearing a tridentate Schiff base ligand produces a novel tricyanoruthenium(III) complex in which nucleophilic substitution of an imine hydrogen of the Schiff base by cyanide has occurred, this complex is a useful building block for the construction of 3d-RuIII magnetic materials.
Co-reporter:Wai-Lun Man ; William W. Y. Lam ; Hoi-Ki Kwong ; Shie-Ming Peng ; Wing-Tak Wong
Inorganic Chemistry 2010 Volume 49(Issue 1) pp:73-81
Publication Date(Web):December 2, 2009
DOI:10.1021/ic901374f
The reaction of [RuVI(N)(L)(MeOH)](PF6) [1; L = N,N′-bis(salicylidene)-o-cyclohexyldiamine dianion] with a stoichiometric amount of RSH in CH3CN gives the corresponding (salen)ruthenium(IV) sulfilamido species [RuIV{N(H)SR}(L)(NCCH3)](PF6) (2a, R = tBu; 2b, R = Ph). Metathesis of 2a with NaN3 in methanol affords [RuIV{N(H)StBu}(L)(N3)] (2c). 2a undergoes further reaction with 1 equiv of RSH to afford a (salen)ruthenium(III) sulfilamine species, [RuIII{N(H)2StBu}(L)(NCCH3)](PF6) (3). On the other hand, 2b reacts with 2 equiv of PhSH to give a (salen)ruthenium(III) ammine species [RuIII(NH3)(L)(NCCH3)](PF6) (4); this species can also be prepared by treatment of 1 with 3 equiv of PhSH. The X-ray structures of 2c and 4 have been determined. Kinetic studies of the reaction of 1 with excess RSH indicate the following schemes: 1 → 2a → 3 (R = tBu), 1 → 2b → 4 (R = Ph). The conversion of 1 to 2 probably involves nucleophilic attack of RSH at the nitrido ligand, followed by a proton shift. The conversions of 2a to 3 and 2b to 4 are proposed to involve rate-limiting H-atom abstraction from RSH by 2a or 2b. 2a and 2b are also able to abstract H atoms from hydrocarbons with weak C−H bonds. These reactions occur with large deuterium isotope effects; the kinetic isotope effect values for the oxidation of 9,10-dihydroanthracene, 1,4-cyclohexadiene, and fluorene by 2a are 51, 56, and 11, respectively.
Co-reporter:Jun-Fang Guo ; Wai-Fun Yeung ; Pui-Ha Lau ; Xiu-Teng Wang ; Song Gao ; Wing-Tak Wong ; Stephen Sin-Yin Chui ; Chi-Ming Che ; Wai-Yeung Wong
Inorganic Chemistry 2010 Volume 49(Issue 4) pp:1607-1614
Publication Date(Web):January 12, 2010
DOI:10.1021/ic9020178
A novel dicyanoosmium(III) complex, trans-Ph4P[OsIII(salen)(CN)2]·CH2Cl2·H2O (1; Ph4P+ = tetraphenylphosphonium cation, salen2− = N,N′-ethylenebis(salicylideneaminato) dianion), has been synthesized and structurally characterized. Reactions of 1 with [Cu(Me3tacn)(H2O)2](ClO4)2 (Me3tacn = 1,4,7-trimethyl-1,4,7-triazacyclononane) under different conditions produce the 1-D ferromagnetic zigzag chains [Os(salen)(CN)2]2[Cu(Me3tacn)]·CH3OH (2) and [Os(salen)(CN)2][Cu(Me3tacn)]·ClO4 (3).
Co-reporter:Wai-Lun Man, Gui Chen, Shek-Man Yiu, Lam Shek, Wai-Yeung Wong, Wing-Tak Wong and Tai-Chu Lau
Dalton Transactions 2010 vol. 39(Issue 46) pp:11163-11170
Publication Date(Web):21 Oct 2010
DOI:10.1039/C0DT00481B
Treatment of [NnBu4][OsVI(N)Cl4] with a stoichiometric amount of H2L (L = N,N′-bis(salicylidene)-o-cyclohexylenediamine dianion) in the presence of PF6− or ClO4− in MeOH affords [OsVI(N)(L)(OH2)](PF6) 1a and [OsVI(N)(L)(CH3OH)](ClO4) 1b, respectively. The structure of 1b has been determined by X-ray crystallography and the OsN bond distance is 1.627(3) Å. In the presence of a N-donor heterocyclic ligand in CH3CN, 1a reacts at room temperature to afford the mixed-valence μ-N2 (salen)osmium species [(X)(L)OsIII–NN–OsII(L)(X)](PF6), 2–14 (X = py 2; 4-Mepy 3; 4-tBupy 4; pz 5; 3-Mepz 6; 3,5-Me2pz 7; Im 8; 1-MeIm 9; 2-MeIm 10; 4-MeIm 11; 1,2-Me2Im 12; 2-Meozl 13; 4-MeTz 14). These complexes are formed by ligand-induced N⋯N coupling of two [OsVIN]+ to give initially [OsIII–N2–OsIII]2+, which is then reduced to give the more stable mixed-valence species [OsIII–N2–OsII]+. Cyclic voltammograms (CVs) of 2–14 show two reversible couples, attributed to OsIII,III/OsIII,II and OsIII,II/OsII,II. The large comproportionation constants (Kcom) of (5.36–82.3) × 1013 indicate charge delocalization in these complexes. The structures of 3 and 14 have been determined by X-ray crystallography, the salen ligands are in uncommon cis-β configuration. Oxidations of 4 and 14 by [Cp2Fe](PF6) afford the symmetrical species [(X)(L)OsIII–NN–OsIII(L)(X)](PF6)2 (X = 4-tBupy 15; 4-MeTz 16). These are the first stable μ-N2 diosmium(III,III) complexes that have been characterized by X-ray crystallography.
Co-reporter:Jun-Fang Guo Dr.;Xiu-Teng Wang Dr.;Bing-Wu Wang Dr.;Guan-Cheng Xu Dr.;Song Gao ;Lap Szeto;Wing-Tak Wong ;Wai-Yeung Wong
Chemistry - A European Journal 2010 Volume 16( Issue 11) pp:3524-3535
Publication Date(Web):
DOI:10.1002/chem.200902047
Abstract
Four cyano-bridged 1D bimetallic polymers have been prepared by using the paramagnetic building block trans-[Ru(acac)2(CN)2]− (Hacac=acetylacetone): {[{Ni(tren)}{Ru(acac)2(CN)2}][ClO4]⋅CH3OH}n (1) (tren=tris(2-aminoethyl)amine), {[{Ni(cyclen)}{Ru(acac)2(CN)2}][ClO4]⋅ CH3OH}n (2) (cyclen=1,4,7,10-tetraazacyclododecane), {[{Fe(salen)}{Ru(acac)2(CN)2}]}n (3) (salen2−=N,N′-bis(salicylidene)-o-ethyldiamine dianion) and [{Mn(5,5′-Me2salen)}2{Ru(acac)2(CN)2}][Ru(acac)2(CN)2]⋅ 2 CH3OH (4) (5,5′-Me2salen=N,N′-bis(5,5′-dimethylsalicylidene)-o-ethylenediimine). Compounds 1 and 2 are 1D, zigzagged NiRu chains that exhibit ferromagnetic coupling between NiII and RuIII ions through cyano bridges with J=+1.92 cm−1, z J′=−1.37 cm−1, g=2.20 for 1 and J=+0.85 cm−1, z J′=−0.16 cm−1, g=2.24 for 2. Compound 3 has a 1D linear chain structure that exhibits intrachain ferromagnetic coupling (J=+0.62 cm−1, z J′=−0.09 cm−1, g=2.08), but antiferromagnetic coupling occurs between FeRu chains, leading to metamagnetic behavior with TN=2.6 K. In compound 4, two MnIII ions are coordinated to trans-[Ru(acac)2(CN)2]− to form trinuclear Mn2Ru units, which are linked together by π–π stacking and weak Mn⋅⋅⋅O* interactions to form a 1D chain. Compound 4 shows slow magnetic relaxation below 3.0 K with ϕ=0.25, characteristic of superparamagnetic behavior. The MnIII⋅⋅⋅RuIII coupling constant (through cyano bridges) and the MnIII⋅⋅⋅MnIII coupling constant (between the trimers) are +0.87 and +0.24 cm−1, respectively. Compound 4 is a novel single-chain magnet built from Mn2Ru trimers through noncovalent interactions. Density functional theory (DFT) combined with the broken symmetry state method was used to calculate the molecular magnetic orbitals and the magnetic exchange interactions between RuIII and M (M=NiII, FeIII, and MnIII) ions. To explain the somewhat unexpected ferromagnetic coupling between low-spin RuIII and high-spin FeIII and MnIII ions in compounds 3 and 4, respectively, it is proposed that apart from the relative symmetries, the relative energies of the magnetic orbitals may also be important in determining the overall magnetic coupling in these bimetallic assemblies.
Co-reporter:Wai-Lun Man;Jing Xiang;Pui-Ha Lau;Song Gao;Wing-Tak Wong
Science China Chemistry 2010 Volume 53( Issue 10) pp:2106-2111
Publication Date(Web):2010 October
DOI:10.1007/s11426-010-4119-4
A series of tricyanoiron(III) complexes with the general formula mer-[FeIII(5-Xsap)(CN)3]2− (X = H, Me, MeO, Cl or Br, sapH2 = N-salicylidene-o-aminophenol) have been synthesized. These complexes were characterized by IR, ESI-MS, UV/Vis, elemental analysis and magnetic measurements. The structures of (PPh4)2[FeIII(sap)(CN)3] and (PPh4)2[FeIII(5-Mesap)(CN)3] have been determined by X-ray crystallography. These low-spin d5 tricyanoiron(III) complexes are potential building blocks for the construction of molecule-based magnets.
Co-reporter:Yi-Ning Wang, Kai-Chung Lau, William W. Y. Lam, Wai-Lun Man, Chi-Fai Leung and Tai-Chu Lau
Inorganic Chemistry 2009 Volume 48(Issue 1) pp:400-406
Publication Date(Web):December 5, 2008
DOI:10.1021/ic8015904
The oxidation of ascorbic acid (H2A) by a trans-dioxoruthenium(VI) species, trans-[RuVI(tmc)(O)2]2+ (tmc = 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane), has been studied in aqueous solutions under argon. The reaction occurs in two phases: trans-[RuVI(tmc)(O)2]2+ + H2A → trans-[RuIV(tmc)(O)(OH2)]2+ + A, trans-[RuIV(tmc)(O)(OH2)]2+ + H2A → trans-[RuII(tmc)(OH2)2]2+ + A. Further reaction involving anation by H2A occurs, and the species [RuIII(tmc)(A2−)(MeOH)]+ can be isolated upon aerial oxidation of the solution at the end of phase two. The rate laws for both phases are first-order in both RuVI and H2A, with the second-order rate constants k2 = (2.58 ± 0.04) × 103 M−1 s−1 at pH = 1.19 and k2′ = (1.90 ± 0.03) M−1 s−1 at pH = 1.24, T = 298 K and I = 0.1 M for the first and second phase, respectively. Studies on the effects of acidity on k2 and k2′ suggest that HA− is the kinetically active species. Kinetic studies have also been carried out in D2O, and the deuterium isotope effects for oxidation of HA− by RuVI and RuIV are 5.0 ± 0.3 and 19.3 ± 2.9, respectively, consistent with a hydrogen atom transfer (HAT) mechanism for both phases. A linear correlation between log(rate constants) for oxidation by RuVI and the O−H bond dissociation energies of HA− and hydroquinones is obtained, which also supports a HAT mechanism.
Co-reporter:Hoi-Ki Kwong ; Wai-Lun Man ; Jing Xiang ; Wing-Tak Wong
Inorganic Chemistry 2009 Volume 48(Issue 7) pp:3080-3086
Publication Date(Web):February 25, 2009
DOI:10.1021/ic802338f
The treatment of [RuVI(N)(L)(MeOH)]PF6 (1) (L = N,N′-bis(salicylidene)-o-cyclohexyldiamine dianion) with 2 equiv of RNC (R = (a) tBu, (b) Cy) in CH2Cl2 affords a mixture of blue cis-β-[RuIII(NCNR)(L)(CNR)] (2) and green trans-[RuIII(L)(CNR)2]PF6 (3) products. The reduction of 3 with a stoichiometric amount of Cp2Co in CH3CN gives red trans-[RuII(L)(CNR)2] (4). Refluxing 4 with 3 equiv of RNC in methanol in the presence of 5 equiv of NH4PF6 affords a yellow complex, mer-[RuII(η3-HL)(CNR)3](PF6) (5), in which the ligand is in an η3-coordination mode. These complexes are characterized by IR, UV−vis, ESI-MS, CV, magnetic measurements, and CHN elemental analysis. The structures of 2a, 3a, 4a, 4b, and 5a have been determined by X-ray crystallography.
Co-reporter:Raymond Wai-Yin Sun, Miro Fei-Yeung Ng, Ella Lai-Ming Wong, Jingfei Zhang, Stephen Sin-Yin Chui, Lam Shek, Tai-Chu Lau and Chi-Ming Che
Dalton Transactions 2009 (Issue 48) pp:10712-10716
Publication Date(Web):14 Sep 2009
DOI:10.1039/B912236B
An oxo-bridged diruthenium(III) complex containing pyrazolato and pyrazole ligands is stable against ascorbic-acid reduction, induces apoptosis (60%, 48 h) against HeLa cells at 10 μM level and exhibits promising anti-angiogenic activity at its sub-cytotoxic concentrations. Other mononuclear ruthenium(III) complexes containing pyrazole ligands [Ru(pz)4X2]+ exhibit dual anti-angiogenic and cytotoxic properties.
Co-reporter:Chi-Fai Leung, Douglas T.Y. Yiu, Wing-Tak Wong, Shie-Ming Peng, Tai-Chu Lau
Inorganica Chimica Acta 2009 Volume 362(Issue 10) pp:3576-3582
Publication Date(Web):1 August 2009
DOI:10.1016/j.ica.2009.04.002
A series of osmium(VI) nitrido complexes containing pyridine-carboxylato ligands OsVI(N)(L)2X (L = pyridine-2carboxylate (1), 2-quinaldinate (2) and X = Cl (a), Br (1b and 2c) or CH3O (2b)) and [OsVI(N)(L)X3]− (L = pyridine-2,6-dicarboxylate (3) and X = Cl (a) or Br (b)) have been synthesised. Complexes 1 and 2 are electrophilic and react readily with various nucleophiles such as phosphine, sulfide and azide. Reaction of OsVI(N)(L)2X (1 and 2) with triphenylphosphine produces the osmium(IV) phosphiniminato complexes OsVI(NPPh3)(L)2X (4 and 5). The kinetics of nitrogen atom transfer from the complexes OsVI(N)(L)2Br (2c) (L = 2-quinaldinate) with triphenylphosphine have been studied in CH3CN at 25.0 °C by stopped-flow spectrophotometric method. The following rate law is obtained: −d[Os(VI)]/dt = k2[Os(VI)][PPh3]. OsVI(N)(L)2Cl (L = 2-quinaldinate) (2a) reacts also with [PPN](N3) to give an osmium(III) dichloro complex, trans-[PPN][OsIII(L)2Cl2] (6). Reaction of OsVI(N)(L)2Cl (L = 2-quinaldinate) (2a) with lithium sulfide produces an osmium(II) thionitrosyl complex OsII(NS)(L)2Cl (7). These complexes have been structurally characterised by X-ray crystallography.A series of electrophilc osmium(VI) nitrido complexes containing pyridine-carboxylato ligands, OsVI(N)(L)2X and [OsVI(N)(L)X3]− have been prepared. OsVI(N)(L)2X reacts readily with phosphine, sulfide and azide, to produce the corresponding OsVI(NPPh3)(L)2X, OsII(NS)(L)2X and trans-[PPN][OsIII(L)2X2] respectively.
Co-reporter:Chi-Fai Leung, Chun-Yuen Wong, Chi-Chiu Ko, Man-Chong Yuen, Wing-Tak Wong, Wai-Yeung Wong, Tai-Chu Lau
Inorganica Chimica Acta 2009 Volume 362(Issue 4) pp:1149-1157
Publication Date(Web):2 March 2009
DOI:10.1016/j.ica.2008.05.036
Reduction of RuQ3 (1a, Q = 8-quinolinolato) with Zn/Hg in the presence of various π-acceptor ligands in ethanol affords RuQ2L2 (L2 = (dimethylsulfoxide)2 (2); (4-picoline)2 (3); N,N′-dimethyl-1,4-diazabuta-1,3-diene, dab (4); cyclooctadiene, COD (5); norborna-2,5-diene, nbd (6)). Compound 6 is isolated as an equimolar mixture of cis,trans (6a) and trans,cis (6b) isomers, which can be separated by column chromatography. DFT calculations have been performed on 6a and 6b. Oxidation of 3 and 6b affords the corresponding ruthenium(III) species 7 and 8, respectively. The structures of 2, 3, 4 and 6 have been determined by X-ray crystallography.Reduction of RuQ3 in the presence of various π-acceptor ligands (L) such as dmso, 4-picoline and alkenes affords RuIIQ2L2. Two geometric isomers of RuQ2(nbd) have been isolated (nbd = norborna-2,5-diene) and structurally characterized; DFT calculations have also been performed on these two compounds. Oxidation of ruthenium(II) (for L = picoline and norbornadiene) gives the corresponding ruthenium(III) species.
Co-reporter:Chi-Fai Leung, Siu-Mui Ng, Jing Xiang, Wai-Yeung Wong, Michael Hon-Wah Lam, Chi-Chiu Ko and Tai-Chu Lau
Organometallics 2009 Volume 28(Issue 19) pp:5709-5714
Publication Date(Web):September 16, 2009
DOI:10.1021/om900253h
A series of ruthenium(II) bis(8-quinolinolato) complexes bearing isocyanide ligands (RNC) have been synthesized by the reaction of [RuQ3] (Q = 8-quinolinolate) with RNC in the presence of Zn/Hg. These complexes have the general formula [RuQ2(RNC)2] (1, R = tert-butyl; 2, R = 4-MeOPh; 3, R = 4-ClPh; 4, R = 2,4,6-Br3Ph). Both the yellow cis,cis,trans (a) and orange-red trans,trans,trans (b) isomers have been isolated for complexes 1−4. trans,trans,trans-[Ru(Tol-Q)2(tBuNC)2] (6, HTol-Q = 8-hydroxyl-5-tolylquinoline) has also been prepared from [Ru(PPh3)2Cl2]. The structures of 2a, 3a, and 4b have been determined by X-ray crystallography. These complexes exhibit an intense absorption band in the UV region (λmax = 320−390 nm) with molar extinction coefficients (ε) on the order of 104 dm3 mol−1 cm−1 and a moderately intense absorption with ε on the order of 103 dm3 mol−1 cm−1 at 400−492 nm. The intense absorption at 320−390 nm is assigned to the ligand-centered π→π* transitions of the quinolinolate ligands, probably mixed with the π→π* transitions of the isocyanide ligands. The lower energy absorptions at 400−492 nm are assigned to Ru(dπ)→π*(Q) metal-to-ligand charge transfer (MLCT) transitions. Upon excitation at λ > 350 nm, 1a−3a in dichloromethane solution exhibit orange-red luminescence (645−680 nm). In 77 K EtOH/MeOH glass, complexes 1−4 and 6 give intense structured emission spectra (593−638 nm). The cyclic voltammograms (CV) of 1a−4a generally exhibit an irreversible or quasi-reversible RuIII/II couple at the potential range of 0.02−0.38 V vs Fc+/Fc, except in the case of 1a, where a reversible RuIII/II and a quasi-reversible RuIV/III (0.68 V vs Fc+/Fc) couple are observed. The potential for the RuIII/II couple increases with the π-accepting ability of the isocyanide ligands. In the CV of 1b−4b, a reversible RuIII/II (−0.16 to 0.065 V) and quasi-reversible RuIV/III (0.70−0.85 V) couple are observed.
Co-reporter:William W. Y. Lam ; Wai-Lun Man ; Yi-Ning Wang
Inorganic Chemistry 2008 Volume 47(Issue 15) pp:6771-6778
Publication Date(Web):July 2, 2008
DOI:10.1021/ic8003849
The kinetics and mechanisms of the oxidation of I− and Br− by trans-[RuVI(N2O2)(O)2]2+ have been investigated in aqueous solutions. The reactions have the following stoichiometry: trans-[RuVI(N2O2)(O)2]2+ + 3X− + 2H+ → trans-[RuIV(N2O2)(O)(OH2)]2+ + X3− (X = Br, I). In the oxidation of I− the I3−is produced in two distinct phases. The first phase produces 45% of I3− with the rate law d[I3−]/dt = (ka + kb[H+])[RuVI][I−]. The remaining I3− is produced in the second phase which is much slower, and it follows first-order kinetics but the rate constant is independent of [I−], [H+], and ionic strength. In the proposed mechanism the first phase involves formation of a charge-transfer complex between RuVI and I−, which then undergoes a parallel acid-catalyzed oxygen atom transfer to produce [RuIV(N2O2)(O)(OHI)]2+, and a one electron transfer to give [RuV(N2O2)(O)(OH)]2+ and I•. [RuV(N2O2)(O)(OH)]2+ is a stronger oxidant than [RuVI(N2O2)(O)2]2+ and will rapidly oxidize another I− to I•. In the second phase the [RuIV(N2O2)(O)(OHI)]2+ undergoes rate-limiting aquation to produce HOI which reacts rapidly with I− to produce I2. In the oxidation of Br− the rate law is −d[RuVI]/dt = {(ka2 + kb2[H+]) + (ka3 + kb3[H+]) [Br−]}[RuVI][Br−]. At 298.0 K and I = 0.1 M, ka2 = (2.03 ± 0.03) × 10−2 M−1 s−1, kb2 = (1.50 ± 0.07) × 10−1 M−2 s−1, ka3 = (7.22 ± 2.19) × 10−1 M−2 s−1 and kb3 = (4.85 ± 0.04) × 102 M−3 s−1. The proposed mechanism involves initial oxygen atom transfer from trans-[RuVI(N2O2)(O)2]2+ to Br− to give trans-[RuIV(N2O2)(O)(OBr)]+, which then undergoes parallel aquation and oxidation of Br−, and both reactions are acid-catalyzed.
Co-reporter:Wai-Lun Man ; Hoi-Ki Kwong ; William W. Y. Lam ; Jing Xiang ; Tsz-Wing Wong ; Wing-Hong Lam ; Wing-Tak Wong ; Shie-Ming Peng
Inorganic Chemistry 2008 Volume 47(Issue 13) pp:5936-5944
Publication Date(Web):May 30, 2008
DOI:10.1021/ic800263n
Reaction of [RuVI(N)(L1)(MeOH)]+ (L1 = N,N′-bis(salicylidene)-o-cyclohexylenediamine dianion) with excess pyridine in CH3CN produces [RuIII(L1)(py)2]+ and N2. The proposed mechanism involves initial equilibrium formation of [RuVI(N)(L1)(py)]+, which undergoes rapid N···N coupling to produce [(py)(L1)RuIIIN≡N−RuIII(L1)(py)]2+; this is followed by pyridine substituion to give the final product. This ligand-induced N···N coupling of RuVI≡N is utilized in the preparation of a series of new ruthenium(III) salen complexes, [RuIII(L)(X)2] ± (L = salen ligand; X = H2O, 1-MeIm, py, Me2SO, PhNH2, tBuNH2, Cl− or CN−). The structures of [RuIII(L1)(NH2Ph)2](PF6) (6), K[RuIII(L1)(CN)2] (9), [RuIII(L2)(NCCH3)2][AuI(CN)2] (11) (L2 = N,N′-bis(salicylidene)-o-phenylenediamine dianion) and [NnBu4][RuIII(L3)Cl2] (12) (L3 = N,N′-bis(salicylidene)ethylenediamine dianion) have been determined by X-ray crystallography.
Co-reporter:Chun-Yuen Wong, Wai-Lun Man, Chao Wang, Hoi-Lun Kwong, Wai-Yeung Wong and Tai-Chu Lau
Organometallics 2008 Volume 27(Issue 3) pp:324-326
Publication Date(Web):January 16, 2008
DOI:10.1021/om701166y
Hydrogen-bridged dinuclear ruthenium carbene complexes supported by salen have been prepared and found to be active catalysts for the cyclopropanation of alkenes; electrochemical and theoretical studies suggest the existence of electronic communication between the Ru centers.
Co-reporter:Chi-Fai Leung;Tsz-Wing Wong;Wing-Tak Wong
European Journal of Inorganic Chemistry 2005 Volume 2005(Issue 4) pp:
Publication Date(Web):25 FEB 2005
DOI:10.1002/ejic.200400539
A series of osmium(VI) nitride complexes containing 8-quinolinolato ligands, [OsVI(N)(X-Q)2Cl] (X = H, 5-Cl, 5-NO2, 2-Me; 1a–d), have been synthesized by reaction of HX-Q with [nBu4N][OsVI(N)Cl4] in the presence of 2,6-dimethylpyridine. The ν(Os≡N) stretches of these compounds occur at 1056–1075 cm–1, and are within the range (1050–1120 cm–1) found for most osmium nitride species. The structure of 1d has been determined by X-ray crystallography. The osmium center adopts a distorted octahedral geometry, and the two quinolinolato ligands are cis to each other. The three N atoms are in a facial arrangement, and the Os≡N bond distance is 1.644(6) Å. Complex 1c readily reacts with the carbene precursors bis(1,3-dialkylimidazolidin-2-ylidene) (LR2; R = Me, Et, or CH2Ph) to produce the osmium(IV) azavinylidene species, [OsIV(N=LR)(NO2-Q)2Cl], which are derived from the formal addition of the carbenes LR to OsVI≡N. The structure of [OsIV(N=LEt)(NO2-Q)2Cl] (2b) has been determined by X-ray crystallography. The osmium center has a distorted octahedral geometry in which the facial arrangement of the three N atoms is retained. The Os(1)–N(5) distance of 1.875(6) Å is rather long and, together with the rather acute Os(1)–N(5)–C(19) angle of 133.8(5)°, indicates that there is no significant multiple-bond character in the Os(1)–N(5) bond. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)
Co-reporter:Sammi K. W. Yau, Chi-Ming Che and Tai-Chu Lau
Dalton Transactions 2002 (Issue 13) pp:2697-2701
Publication Date(Web):24 May 2002
DOI:10.1039/B202230C
The kinetics of the reduction of cis-[RuVIL(O)2]2+ (L =
N,N,N′,N′-tetramethyl-3,6-dimethyl-3,6-diazaoctane-1,8-diamine) by [Ni(tacn)2]2+ (tacn = 1,4,7-triazacyclononane) and [Fe(H2O)6]2+ have been studied in aqueous acidic solutions. Both reactions have the following stoichiometry: 2MII
+
cis-[RuVIL(O)2]2+
+ 2H+
→ 2MIII
+
cis-[RuIVL(O)(OH2)]2+ (M = Ni or Fe). Two distinct steps were observed for both reactions and these are assigned to RuVI
→ RuV and RuV
→ RuIV. Both steps are first order in [RuVI] and [MII]. For the reduction by [Ni(tacn)2]2+, the
activation parameters (I
= [H+] = 0.1 mol dm−3) for the first step are ΔH‡
= 13.4 ± 1.0 kJ mol−1 and ΔS‡
=
−111 ± 10 J mol−1 K−1; for the second reaction, ΔH‡
= 28.5 ± 1.5 kJ mol−1 and ΔS‡
=
−110 ± 10 J mol−1 K−1. The rate constant for the first step is independent of acid concentration, an outer-sphere mechanism is proposed and a self-exchange rate of 2 × 104 dm3 mol−1 s−1 for the cis-[RuVIL(O)2]2+/cis-[RuVL(O)2]+ couple is estimated using the Marcus cross-relation. The rate constant
of the second step increases with [H+] and it reaches saturation at high [H+]. A mechanism involving a pre-equilibrium protonation of cis-[RuVL(O)2]+ followed by outer-sphere electron transfer is proposed. For the reduction by [Fe(H2O)6]2+, rate constants for both steps are independent of acid concentration in the range of pH = 1–3. The activation parameters (I
= 1.0 mol dm−3, pH = 1.0) for the first step are ΔH‡
= 32.5 ± 1.5 kJ mol−1 and ΔS‡
=
−52.5 ± 7 J mol−1 K−1; while for the second step, ΔH‡
= 17.3 ± 1.2 kJ mol−1 and ΔS‡
=
−140 ± 13 J mol−1
K−1. An outer-sphere mechanism is proposed for the first step and an inner-sphere mechanism is proposed for the second step.
Co-reporter:Wai-Fun Yeung, Song Gao, Wing-Tak Wong and Tai-Chu Lau
New Journal of Chemistry 2002 vol. 26(Issue 5) pp:523-525
Publication Date(Web):15 Apr 2002
DOI:10.1039/B111012H
Reaction of Na[N(CN)2] with CuSO4·5H2O and 2,5-Me2pyz produced {Cu2(2,5-Me2pyz)[N(CN)2]4}n
(2,5-Me2pyz=2,5-dimethylpyrazine), which is an unusual five-connected, two-fold interpenetrated network that orders antiferromagnetically at low temperature.
Co-reporter:Iris P. Y. Shek, Wing-Tak Wong, Song Gao and Tai-Chu Lau
New Journal of Chemistry 2002 vol. 26(Issue 9) pp:1099-1101
Publication Date(Web):11 Jul 2002
DOI:10.1039/B203077B
Reaction of K4[Fe(CN)6] with Ni(CH3COO)2 and cyclen produced an unusual one-dimensional paramagnetic complex, [Ni(cyclen)]2[Fe(CN)6]·8H2O (cyclen=1,4,7,10-tetraazacyclododecane), that consists of [Ni(cyclen)]2 dimers bridged by μ3-cyanides from [Fe(CN)6]4−. The Ni⋯Ni distance is 3.303 Å, which is significantly shorter than the corresponding distance of 3.449 Å in [Ni2(μ-N3)2(232-tet)2](PF6)2. Moderate antiferromagnetic coupling occurs between the Ni2+ ions.
Co-reporter:Wai-Fun Yeung;Wai-Lun Man;Wing-Tak Wong ;Song Gao
Angewandte Chemie 2001 Volume 113(Issue 16) pp:
Publication Date(Web):15 AUG 2001
DOI:10.1002/1521-3757(20010817)113:16<3121::AID-ANGE3121>3.0.CO;2-U
Eine durch Cyanobrücken vermittelte Wechselwirkung der alternierend angeordneten High-Spin-MnII- und Low-Spin-RuIII-Zentren in {Mn[Ru(acac)2(CN)2]2}n (Hacac=Acetylaceton) hat unterhalb von 3.6 K eine weit reichende ferromagnetische Ordnung zur Folge. Dieses neuartige MnIIRuIII-Koordinationspolymer mit diamantartiger Struktur (siehe Bild) wurde aus [Ru(acac)2(CN)2]− und Mn2+ erhalten.
Co-reporter:Wai-Fun Yeung, Wing-Tak Wong, Jing-Lin Zuo and Tai-Chu Lau
Dalton Transactions 2000 (Issue 5) pp:629-631
Publication Date(Web):28 Feb 2000
DOI:10.1039/A910350N
Two novel cyano CuII–AuI bimetallic complexes, Cu(cyclen)[Au(CN)2]21 (cyclen = 1,4,7,10-tetraazacyclododecane) and Cu(pyz)[Au(CN)2]22 (pyz = pyrazine) were prepared; 1 has a dimeric structure arising from AuI⋯AuI interactions, while 2 consists of linear pyrazine-bridged copper chains intercalated to produce a 2-D pleated sheet structure.
Co-reporter:Douglas T. Y. Yiu, Kwok-Ho Chow and Tai-Chu Lau
Dalton Transactions 2000 (Issue 1) pp:17-20
Publication Date(Web):14 Jan 2000
DOI:10.1039/A907664F
The kinetics of the oxidation of hypophosphite and phosphite by trans-[Ru(L)(O)2]2+ (L = 1,12-dimethyl-3,4∶9,10-dibenzo-1,12-diaza-5,8-dioxacyclopentadecane) have been studied in aqueous acidic solutions. The reactions have the following stoichiometry (x = 2 or 3): trans-[RuVI(L)(O)2]2+ + H2POx− + H2O → trans-[RuIV(L)(O)(OH2)]2+ + H2POx + 1−. The two reactions have the same rate law (P = hypophosphite or phosphite): −d[RuVI]/dt = k/(1 + [H+]/K)[RuVI][P]. For hypophosphite, k = (1.3 ± 0.1) dm3 mol−1 s−1 and K = (9.7 ± 0.5) × 10−2 mol dm−3 at 298 K and I = 1.0 mol dm−3. For phosphite, k = (4.8 ± 0.4) × 10−2 dm3 mol−1 s−1 and K = (1.2 ± 0.2) × 10−2 mol dm−3 at 298 K and I = 0.2 mol dm−3. The effects of temperature were studied from 15 °C to 40 °C. For hypophosphite, ΔH‡ = (60 ± 2) kJ mol−1 and ΔS‡ = (−41 ± 4) J mol−1 K−1 at pH = 1.86 and I = 1.0 mol dm−3. For phosphite, ΔH‡ = (59 ± 4) kJ mol−1 and ΔS‡ = (−75 ± 13) J K−1 mol−1 at pH = 2.3 and I = 0.2 mol dm−3. Deuterium isotope effects have also been investigated. For hypophosphite, the kinetic isotope effect, k(H2PO2−)/k(D2PO2−) is 4.1 at pH = 1.07 and I = 1.0 mol dm−3. For phosphite, the kinetic isotopic effect, k(HDPO3−)/k(D2PO3−), is 4.0 at pH = 2.30 at I = 0.2 mol dm−3. A mechanism involving hydride transfer from P–H to RuO is proposed for these two reactions.
Co-reporter:Iris P. Y. Shek, Wai-Yeung Wong and Tai-Chu Lau
New Journal of Chemistry 2000 vol. 24(Issue 10) pp:733-734
Publication Date(Web):15 Sep 2000
DOI:10.1039/B004939P
Reaction of nickel(II) acetate with cyclen (cyclen=1,4,7,10-tetraazacyclododecane) and K[Ag(CN)2] gave {[Ni(cyclen)][Ag(CN)2]}[Ag(CN)2], which consists of cis-[Ni(cyclen)]2+
units bridged by [Ag(CN)2]− to form a zig-zag chain; the Ag atoms of the free and bridging [Ag(CN)2]−
also align together to form an infinite zig-zag chain with short Ag···Ag distances.
Co-reporter:Ivan K. Chu, Iris P. Y. Shek, K. W. Michael Siu, Wing-Tak Wong, Jing-Lin Zuo and Tai-Chu Lau
New Journal of Chemistry 2000 vol. 24(Issue 10) pp:765-769
Publication Date(Web):18 Sep 2000
DOI:10.1039/B003673K
Reaction of nickel(II) acetate with tren [tren=tris(2-aminoethyl)amine] and K[Au(CN)2] produced [Ni(tren)Au(CN)2][Au(CN)2] (1), which consists of cis-[Ni(tren)]2+ units linked by Au(CN)2− to form infinite zig-zag chains. The complex obeys the Curie–Weiss law throughout the temperature range 4–300 K, with a Curie constant of 1.10 cm3 K mol−1
and a Weiss temperature, θ, of 0.62 K. The electrospray mass spectrum of 1 in H2O–CH3OH shows peaks that can
be described by the general formulae {[Ni(tren)]n[Au(CN)2]2n−1}+ (n=1–4) and {[Ni(tren)]n[Au(CN)2]2n−2}2+ (n=2–9). Based on the
crystal structure of the polymer, these ions are best described as composed of an oligomeric cation that may be associated with one or more Au(CN)2− counter ions.
Co-reporter:Chi-Ming Ho and Tai-Chu Lau
New Journal of Chemistry 2000 vol. 24(Issue 11) pp:859-863
Publication Date(Web):09 Oct 2000
DOI:10.1039/B004286M
The
catalytic activity of a number of copper complexes and salts toward allylic amination of alkenes using
phenylhydroxylamine as the nitrogen fragment donor has been investigated. The best catalyst is CuCl2·2H2O, which produces moderate yields of allylamines with high regioselectivity resulting from double bond transposition. A mechanism
similar to that for the molybdenum and the FePc systems is proposed. The first step in the catalytic cycle is
the formation of nitrosobenzene from the oxidation of phenylhydroxylamine by Cu(II). The next step is an ene
reaction of the alkene with PhNO to produce an allylhydroxylamine, which is then reduced to the allylamine product by Cu(I), thus regenerating Cu(II). The same system can also transfer the nitrogen fragment to the α-carbon of cyclic ketones; this
is accompanied
by dehydrogenation
in some cases to produce α-aminated, α,β-unsaturated ketones.
Co-reporter:Chi-Ming Ho and Tai-Chu Lau
New Journal of Chemistry 2000 vol. 24(Issue 8) pp:587-590
Publication Date(Web):06 Jul 2000
DOI:10.1039/B002907F
In the presence of a few equivalents of a metal chloride, barium ferrate (BaFeO4) has been found to oxidize cyclohexane at room temperature in acetic acid–dichloromethane to give a mixture of chlorocyclohexane, cyclohexanol and cyclohexanone. The rates of oxidation for the various metal chlorides follow
the order AlCl3>FeCl3>MgCl2>LiCl>ZnCl2. The best yield was obtained with MgCl2, which represents a balance between reactivity and stability. Oxidation of other organic substrates has also been carried out using the BaFeO4–LiCl system. Notably the system is able to oxidize propane and ethane to give a mixture of chloroalkanes and carbonyl
products. The deuterium isotope effect for the oxidation of cyclohexane was found to be 2.1, 1.8, and 3.0 for chlorocyclohexane,
cyclohexanol and cyclohexanone, respectively. The active intermediate is proposed to be a Lewis acid–ferrate
adduct formed by coordination of an oxo ligand of the ferrate to the metal ion. It is suggested that the reactivity
of this adduct is reminiscent
of a radical species that oxidizes alkanes ia a hydrogen atom abstraction pathway.
Co-reporter:Ruwei Wang, Guijian Liu, Tai-Chu Lau
Applied Catalysis A: General (25 April 2015) Volume 496() pp:17-24
Publication Date(Web):25 April 2015
DOI:10.1016/j.apcata.2015.02.004
Co-reporter:Jianhui Xie, Po-Kam Lo, William W. Y. Lam, Wai-Lun Man, Li Ma, Shek-Man Yiu, Kai-Chung Lau and Tai-Chu Lau
Chemical Communications 2016 - vol. 52(Issue 76) pp:NaN11433-11433
Publication Date(Web):2016/08/19
DOI:10.1039/C6CC06231H
Hydroquinone is readily oxidized by a (salen)ruthenium(VI) nitrido complex in the presence of pyridine to give benzoquinone. Experimental and computational studies suggest that the reaction occurs via a novel mechanism that involves an initial electrophilic attack at the aromatic ring of the hydroquinone by the nitrido ligand.
Co-reporter:Gui Chen, Lingjing Chen, Li Ma, Hoi-Ki Kwong and Tai-Chu Lau
Chemical Communications 2016 - vol. 52(Issue 59) pp:NaN9274-9274
Publication Date(Web):2016/06/22
DOI:10.1039/C6CC04173F
Mn(V) nitrido complex [Mn(N)(CN)4]2− is an efficient catalyst for visible-light induced oxidation of alkenes and alcohols in water using [Ru(bpy)3]2+ as a photosensitizer and [Co(NH3)5Cl]2+ as a sacrificial oxidant. Alkenes are oxidized to epoxides and alcohols to carbonyl compounds.
Co-reporter:Man Chen, Yi Pan, Hoi-Ki Kwong, Raymond J. Zeng, Kai-Chung Lau and Tai-Chu Lau
Chemical Communications 2015 - vol. 51(Issue 71) pp:NaN13689-13689
Publication Date(Web):2015/07/20
DOI:10.1039/C5CC03636D
The osmium(VI) nitrido complex, [OsVI(N)(L)(CH3OH)]+ (1, L = N,N′-bis(salicylidene)-o-cyclohexyldiamine dianion) is an efficient catalyst for the oxidation of alkanes under ambient conditions using H2O2 as the oxidant. Alkanes are oxidized to the corresponding alcohols and ketones, with yields up to 75% and turnover numbers up to 2230. Experimental and computational studies are consistent with a mechanism that involves O-atom transfer from H2O2 to [OsVI(N)(L)]+ to generate an [OsVIII(N)(O)(L)]+ active intermediate.
Co-reporter:Quan Tang, Wen-Xiu Ni, Chi-Fai Leung, Wai-Lun Man, Kenneth King-Kwan Lau, Yimin Liang, Yun-Wah Lam, Wai-Yeung Wong, Shie-Ming Peng, Gui-Jian Liu and Tai-Chu Lau
Chemical Communications 2013 - vol. 49(Issue 85) pp:NaN9982-9982
Publication Date(Web):2013/08/28
DOI:10.1039/C3CC42250J
A series of osmium(VI) nitrido complexes supported by quinolinolato ligands have been prepared and they exhibit promising in vitro anti-cancer activities. These results establish that OsVIN is a potentially versatile and promising platform for the design of a variety of high-valent anti-cancer drugs.
Co-reporter:Man Chen, Siu-Mui Ng, Shek-Man Yiu, Kai-Chung Lau, Raymond J. Zeng and Tai-Chu Lau
Chemical Communications 2014 - vol. 50(Issue 95) pp:NaN14959-14959
Publication Date(Web):2014/10/10
DOI:10.1039/C4CC07607A
A double-helical dicobalt(II) complex [Co2(spy)2](ClO4)4 (spy = 2,2′:6′,2″:6″,2‴:6‴,2⁗:6⁗,2⁗′-sexipyridine) (1) is found to catalyze visible light-induced water oxidation by [Ru(bpy)3]2+/Na2S2O8, with a maximum turnover number of 442. Several lines of evidence suggest that 1 functions as a molecular catalyst and does not produce any CoOx in water oxidation.
Co-reporter:Qian Wang, Wai-Lun Man, William W. Y. Lam and Tai-Chu Lau
Chemical Communications 2014 - vol. 50(Issue 99) pp:NaN15802-15802
Publication Date(Web):2014/11/05
DOI:10.1039/C4CC07568D
The oxidation of ascorbic acid (H2A) by [RuVI(N)(L)(MeOH)]+ in aqueous acidic solutions has the following stoichiometry: 2[RuVI(N)] + 3H2A → 2[RuIII(NH2–HA)]+ + A. Mechanisms involving HAT/N-rebound at low pH (≤2) and nucleophilic attack at the nitride at high pH (≥5) are proposed.
Co-reporter:Wen-Xiu Ni, Wai-Lun Man, Myra Ting-Wai Cheung, Raymond Wai-Yin Sun, Yuan-Lan Shu, Yun-Wah Lam, Chi-Ming Che and Tai-Chu Lau
Chemical Communications 2011 - vol. 47(Issue 7) pp:NaN2142-2142
Publication Date(Web):2011/01/04
DOI:10.1039/C0CC04515B
A nitridoosmium(VI) complex [OsVI(N)(sap)(OH2)Cl] (H2sap = N-salicylidene-2-aminophenol) displays prominent in vitro and in vivo anti-cancer properties, induces S- and G2/M-phase arrest and forms a stable adduct with dianionic 5′-guanosine monophosphate.
Co-reporter:Jing Xiang, Li-Hui Jia, Wai-Lun Man, Kang Qian, Shek-Man Yiu, Gene-Hsiang Lee, Shie-Ming Peng, Song Gao and Tai-Chu Lau
Chemical Communications 2011 - vol. 47(Issue 30) pp:NaN8696-8696
Publication Date(Web):2011/07/02
DOI:10.1039/C1CC12446C
Reaction of [RuII(PPh3)3Cl2] with HQ and KCN produces a new dicyanoruthenium(III) building block, [RuIII(Q)2(CN)2]−. It reacts with hydrated CoCl2 in MeOH or DMF to produce a trinuclear compound 2 or a 1-D zigzag chain 3.
Co-reporter:Jing Xiang, Wai-Lun Man, Junfang Guo, Shek-Man Yiu, Gene-Hsiang Lee, Shie-Ming Peng, Guancheng Xu, Song Gao and Tai-Chu Lau
Chemical Communications 2010 - vol. 46(Issue 33) pp:NaN6104-6104
Publication Date(Web):2010/07/26
DOI:10.1039/C001732A
Reaction of excess cyanide with a ruthenium(VI) nitrido complex bearing a tridentate Schiff base ligand produces a novel tricyanoruthenium(III) complex in which nucleophilic substitution of an imine hydrogen of the Schiff base by cyanide has occurred, this complex is a useful building block for the construction of 3d-RuIII magnetic materials.
Co-reporter:Chi-Fai Leung, Shek-Man Yiu, Jing Xiang and Tai-Chu Lau
Chemical Communications 2010 - vol. 46(Issue 40) pp:NaN7577-7577
Publication Date(Web):2010/09/17
DOI:10.1039/C0CC01645D
Reaction of RuVIN complexes bearing 8-quinolinolato ligands with NCCH2CN/piperidine and NaTCNE afford novel ruthenium(II) dicyanoimine and diimine/imino-oxazolone complexes, respectively.
Co-reporter:Jing Xiang, Li-Hui Jia, Bing-Wu Wang, Shek-Man Yiu, Shie-Ming Peng, Wai-Yeung Wong, Song Gao and Tai-Chu Lau
Dalton Transactions 2013 - vol. 42(Issue 11) pp:NaN3887-3887
Publication Date(Web):2013/01/16
DOI:10.1039/C2DT32331A
The synthesis, crystal structures and magnetic properties of six cyano-bridged heterobimetallic compounds prepared from a paramagnetic RuIII building block, trans-(PPh4)[RuIII(Q)2(CN)2] (1) (Q = the anion of 8-hydroxyquinoline), are described. 1 reacts with hydrated MnCl2 in MeOH or DMF to produce a trinuclear compound {[RuIII(Q)2(CN)2]2[MnII(MeOH)4]}·8MeOH (2), or a 1-D zigzag chain {[MnII(DMF)2(Cl)](μ-CN)2[RuIII(Q)2]}n(3). The MnII has a distorted octahedral environment in 2 and a trigonal-bipyramidal environment in 3. 1 reacts with [MnIII(L1)(Cl)(H2O)] in MeOH to produce the 1-D {[RuIII(Q)2](μ-CN)2[MnIII(L1)]}n (4) that consists of alternating MnIII and RuIII units. 1 also reacts with [CuII(cyclam)Br2] and [NiII(cyclam)Cl2] in MeOH to produce the trinuclear complexes [RuIII(Q)2(CN2)]2[MII(cyclam)] (M = CuII (5) and NiII (6)). On the other hand, the reaction of 1 with [NiII(cyclen)Cl2] produces a 1-D zigzag chain {([RuIII(Q)2(CN2)][NiII(cyclen)])[RuIII(Q)2(CN2)]}n (7). Compounds 2–4 exhibit antiferromagnetic coupling between RuIII and MnIII/II centres. Antiferromagnetic coupling also occurs between RuIII and CuII centres in 5. On the other hand, compounds 6 and 7 exhibit ferromagnetic coupling between RuIII and NiII through cyanide bridges.
Co-reporter:Jing Xiang, Li-Hui Jia, Wai-Lun Man, Kang Qian, Gene-Hsiang Lee, Shie-Ming Peng, Shek-Man Yiu, Song Gao and Tai-Chu Lau
Dalton Transactions 2012 - vol. 41(Issue 19) pp:NaN5798-5798
Publication Date(Web):2012/02/13
DOI:10.1039/C2DT11810F
Reaction of [RuVI(N)(sap)Cl] with excess NaN3 affords a novel paramagnetic triazidoruthenium(III) complex [RuIII(sap)(N3)3]2−, which is isolated as a PPh4+ salt (1). Reaction of 1 with Ni2+ and Co2+ ions produce two isostructural hexanuclear [Ru4M2] compounds, [RuIV4MII2(μ3-OMe)2(μ-OMe)2(μ-N)2(μ-N3)2(μ-Ophenoxy)2(sap)4 (MeOH)4] (M = Ni 2 or Co 3). The molecular structures of 1–3 have been determined by X-ray crystallography. 1 is a mononuclear ruthenium(III) compound where three azide ligands are bonded to ruthenium in a meridional fashion, while compounds 2 and 3 are isostructural hexanuclear compounds containing a defective face-sharing dicubane-like core with two missing vertexes. Variable-temperature dc magnetic susceptibility studies have been carried out for 2 and 3. These data indicate that there are four diamagnetic Ru(IV) ions in 2 and 3 and there is ferromagnetic interaction between the two Ni2+ in 2 and Co2+ in 3via the methoxy bridges.
Co-reporter:Raymond Wai-Yin Sun, Miro Fei-Yeung Ng, Ella Lai-Ming Wong, Jingfei Zhang, Stephen Sin-Yin Chui, Lam Shek, Tai-Chu Lau and Chi-Ming Che
Dalton Transactions 2009(Issue 48) pp:NaN10716-10716
Publication Date(Web):2009/09/14
DOI:10.1039/B912236B
An oxo-bridged diruthenium(III) complex containing pyrazolato and pyrazole ligands is stable against ascorbic-acid reduction, induces apoptosis (60%, 48 h) against HeLa cells at 10 μM level and exhibits promising anti-angiogenic activity at its sub-cytotoxic concentrations. Other mononuclear ruthenium(III) complexes containing pyrazole ligands [Ru(pz)4X2]+ exhibit dual anti-angiogenic and cytotoxic properties.
Co-reporter:Zongmin Hu, Hongxia Du, Wai-Lun Man, Chi-Fai Leung, Haojun Liang and Tai-Chu Lau
Chemical Communications 2012 - vol. 48(Issue 8) pp:NaN1104-1104
Publication Date(Web):2011/11/07
DOI:10.1039/C1CC15860K
cis-[Ru(2,9-Me2phen)2(OH2)2]2+ reacts readily with chlorite at room temperature at pH 4.9 and 6.8. The ruthenium(II) complex can catalyze the disproportionation of chlorite to chlorate and chloride, the oxidation of chlorite to chlorine dioxide, as well as the oxidation of alcohols by chlorite.
Co-reporter:Peng Tan, Hoi-Ki Kwong and Tai-Chu Lau
Chemical Communications 2015 - vol. 51(Issue 61) pp:NaN12192-12192
Publication Date(Web):2015/06/16
DOI:10.1039/C5CC02868J
An iron(III) complex bearing a cross-bridged cyclam ligand (4,11-dimethyl-1,4,8,11-tetraazabicyclo[6.6.2]hexadecane) is an efficient catalyst for the oxidation of both water and alcohols using sodium periodate as the oxidant. In catalytic water oxidation a maximum turnover number (TON) of 1030 is achieved, while in catalytic alcohol oxidation >95% conversions and yields can be obtained.
Co-reporter:Wai-Lun Man, Gui Chen, Shek-Man Yiu, Lam Shek, Wai-Yeung Wong, Wing-Tak Wong and Tai-Chu Lau
Dalton Transactions 2010 - vol. 39(Issue 46) pp:NaN11170-11170
Publication Date(Web):2010/10/21
DOI:10.1039/C0DT00481B
Treatment of [NnBu4][OsVI(N)Cl4] with a stoichiometric amount of H2L (L = N,N′-bis(salicylidene)-o-cyclohexylenediamine dianion) in the presence of PF6− or ClO4− in MeOH affords [OsVI(N)(L)(OH2)](PF6) 1a and [OsVI(N)(L)(CH3OH)](ClO4) 1b, respectively. The structure of 1b has been determined by X-ray crystallography and the OsN bond distance is 1.627(3) Å. In the presence of a N-donor heterocyclic ligand in CH3CN, 1a reacts at room temperature to afford the mixed-valence μ-N2 (salen)osmium species [(X)(L)OsIII–NN–OsII(L)(X)](PF6), 2–14 (X = py 2; 4-Mepy 3; 4-tBupy 4; pz 5; 3-Mepz 6; 3,5-Me2pz 7; Im 8; 1-MeIm 9; 2-MeIm 10; 4-MeIm 11; 1,2-Me2Im 12; 2-Meozl 13; 4-MeTz 14). These complexes are formed by ligand-induced N⋯N coupling of two [OsVIN]+ to give initially [OsIII–N2–OsIII]2+, which is then reduced to give the more stable mixed-valence species [OsIII–N2–OsII]+. Cyclic voltammograms (CVs) of 2–14 show two reversible couples, attributed to OsIII,III/OsIII,II and OsIII,II/OsII,II. The large comproportionation constants (Kcom) of (5.36–82.3) × 1013 indicate charge delocalization in these complexes. The structures of 3 and 14 have been determined by X-ray crystallography, the salen ligands are in uncommon cis-β configuration. Oxidations of 4 and 14 by [Cp2Fe](PF6) afford the symmetrical species [(X)(L)OsIII–NN–OsIII(L)(X)](PF6)2 (X = 4-tBupy 15; 4-MeTz 16). These are the first stable μ-N2 diosmium(III,III) complexes that have been characterized by X-ray crystallography.
Co-reporter:Gui Chen, Wai-Lun Man, Shek-Man Yiu, Tsz-Wing Wong, Lap Szeto, Wing-Tak Wong and Tai-Chu Lau
Dalton Transactions 2011 - vol. 40(Issue 9) pp:NaN1944-1944
Publication Date(Web):2011/01/26
DOI:10.1039/C0DT01367F
The preparation of a number of binuclear (salen)osmium phosphinidine and phosphiniminato complexes using various strategies are described. Treatment of [OsVI(N)(L1)(sol)](X) (sol = H2O or MeOH) with PPh3 affords an osmium(IV) phosphinidine complex [OsIV{N(H)PPh3}(L1)(OMe)](X) (X = PF61a, ClO41b). If the reaction is carried out in CH2Cl2 in the presence of excess pyrazine the osmium(III) phosphinidine species [OsIII{N(H)PPh3}(L1)(pz)](PF6) 2 can be generated. On the other hand, if the reaction is carried out in CH2Cl2 in the presence of a small amount of H2O, a μ-oxo osmium(IV) phosphinidine complex is obtained, [(L1){PPh3N(H)}OsIV–O–OsIV{N(H)PPh3}(L1)](PF6)23. Furthermore, if the reaction of [OsVI(N)(L1)(OH2)]PF6 with PPh3 is done in the presence of 2, the μ-pyrazine species, [(L1){PPh3N(H)}OsIII–pz–OsIII{N(H)PPh3}(L1)](PF6)24 can be isolated. Novel binuclear osmium(IV) complexes can be prepared by the use of a diphosphine ligand to attack two OsVIN. Reaction of [OsVI(N)(L1)(OH2)](PF6) with PPh2–CC–PPh2 or PPh2–(CH2)3–PPh2 in MeOH affords the binuclear complexes [(MeO)(L1)OsIV{N(H)PPh2–R–PPh2N(H)}OsIV(L1)(OMe)](PF6)2 (R = CC 5, (CH2)36). Reaction of [OsVI(N)(L2)Cl] with PPh2FcPPh2 generates a novel trimetallic complex, [Cl(L2)OsIV{NPPh2–Fc–PPh2N}OsIV(L2)Cl] 7. The structures of 1b, 2, 3, 4, 5 and 7 have been determined by X-ray crystallography.
Co-reporter:Jianhui Xie, Li Ma, William W. Y. Lam, Kai-Chung Lau and Tai-Chu Lau
Dalton Transactions 2016 - vol. 45(Issue 1) pp:NaN73-73
Publication Date(Web):2015/11/13
DOI:10.1039/C5DT04303D
The oxidation of phenols by HFeO4− proceeds via a hydrogen atom transfer (HAT) mechanism, as evidenced by a large deuterium isotope effect and a linear correlation between the log(rate constant) and bond dissociation free energy (BDFE) of phenols. The Marcus cross relation has been applied to predict the rate constant of HAT from hydroquinone to HFeO4−.
Co-reporter:Wen-Xiu Ni, Wai-Lun Man, Shek-Man Yiu, Man Ho, Myra Ting-Wai Cheung, Chi-Chiu Ko, Chi-Ming Che, Yun-Wah Lam and Tai-Chu Lau
Chemical Science (2010-Present) 2012 - vol. 3(Issue 5) pp:NaN1588-1588
Publication Date(Web):2012/02/03
DOI:10.1039/C2SC01031C
Eight new nitridoosmium(VI) complexes with the general formula [OsVI(N)Cl3(Hazole)2] have been synthesized and characterized. The cellular uptake and the antiproliferative activities of these compounds against a panel of human cancer cell lines have been investigated. Complexes with pyrazole derivatives (1, 2, 3 and 4) are found to possess significant in vitro cytotoxicity. Further studies of compounds 1 and 3 indicate that they induce S phase arrest in HeLa cells followed by apoptosis, possibly as a result of binding with DNA.
Co-reporter:Hongxia Du, Po-Kam Lo, Zongmin Hu, Haojun Liang, Kai-Chung Lau, Yi-Ning Wang, William W. Y. Lam and Tai-Chu Lau
Chemical Communications 2011 - vol. 47(Issue 25) pp:NaN7145-7145
Publication Date(Web):2011/05/25
DOI:10.1039/C1CC12024G
The oxidation of alcohols by KMnO4 is greatly accelerated by various Lewis acids. Notably the rate is increased by 4 orders of magnitude in the presence of Ca2+. The mechanisms of the oxidation of CH3OH and PhCH(OH)CH3 by MnO4− and BF3·MnO4− have also been studied computationally by the DFT method.
Co-reporter:Hoi-Ki Kwong, Po-Kam Lo, Kai-Chung Lau and Tai-Chu Lau
Chemical Communications 2011 - vol. 47(Issue 14) pp:NaN4275-4275
Publication Date(Web):2011/03/07
DOI:10.1039/C0CC05487A
The manganese(V) nitrido complex (PPh4)2[Mn(N)(CN)4] is an active catalyst for alkene epoxidation and alcohol oxidation using H2O2 as an oxidant. The catalytic oxidation is greatly enhanced by the addition of just one equivalent of acetic acid. The oxidation of ethene by this system has been studied computationally by the DFT method.
Co-reporter:Shek-Man Yiu, Wai-Lun Man, Xin Wang, William W. Y. Lam, Siu-Mui Ng, Hoi-Ki Kwong, Kai-Chung Lau and Tai-Chu Lau
Chemical Communications 2011 - vol. 47(Issue 14) pp:NaN4161-4161
Publication Date(Web):2011/02/28
DOI:10.1039/C1CC00019E
MnO4− is activated by BF3 to undergo intramolecular coupling of two oxo ligands to generate O2. DFT calculations suggest that there should be a spin intercrossing between the singlet and triplet potential energy surfaces on going from the active intermediate [MnO2(OBF3)2]− to the O⋯O coupling transition state.
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