Haiyan Wei - Cochemist

A One-Dimensional Magnet Based on [MoIII(CN)7]4–

Co-reporter:Xiao-Qin Wei, Kun Qian, Hai-Yan Wei, and Xin-Yi Wang

Inorganic Chemistry 2016 Volume 55(Issue 11) pp:5107-5109

Publication Date(Web):May 13, 2016

DOI:10.1021/acs.inorgchem.6b00787

Self-assembly of the [MoIII(CN)7]4– anion and the MnII unit with a macrocyclic ligand results in the first example of a one-dimensional (1D) chain compound based on the heptacyanomolybdate, [Mn(LN5C10)]2[Mo(CN)7]·2H2O (LN5C10 = 1,4,7,10,13-pentaazacyclopentadecane). Because of the existence of the interchain magnetic coupling, long-rang magnetic ordering was observed in this compound.

New Insights into Mechanism of Molybdenum(VI)–Dioxo Complex Catalyzed Hydrosilylation of Carbonyls: An Alternative Model for Activating Si–H Bond

Co-reporter:Xiaoshuang Ning, Jiandi Wang, and Haiyan Wei

The Journal of Physical Chemistry A 2016 Volume 120(Issue 24) pp:4167-4178

Publication Date(Web):May 31, 2016

DOI:10.1021/acs.jpca.6b01978

Recently, a series of oxo/nitrido-ReV/MoVI/RuVI/MnV complexes were demonstrated to be efficient catalysts in activating silanes and catalyzing hydrosilylations of unsaturated organic substrates. In the present study, the high-valent molybdenum(VI)–dioxo complex MoO2Cl2 catalyzed hydrosilylations of carbonyls was reinvestigated using density functional theory method. Previous experimental and theoretical investigations suggested a [2 + 2] addition pathway for MoO2Cl2 catalyzed hydrosilylations of ketones. In the present study, we propose an ionic outer-sphere mechanistic pathway to be the most favorable pathway. The key step in the ionic outer-sphere pathway is oxygen atom of C═O bonds nucleophilically attacking the silicon atom in an η1-silane molybdenum adduct. The Si–H bond is then cleaved heterolytically. This process features a novel SN2@Si transition state, which then generates a loosely bound ion pair: anionic molybdenum hydride paired with silylcarbenium ion ([MoO2Cl2H]− [SiR3(OCR′R″)]+) in solvent. The last step is silylcarbenium ion abstracting the hydride on molybdenum hydride to yield silyl ether. The calculated activation free energy barrier of the rate-determing step was 24.1 kcal/mol for diphenylketone (PhC═OPh) and silane of PhMe2SiH. Furthermore, the ionic outer-sphere pathway is calculated to be ∼10.0 kcal/mol lower than the previously proposed [2 + 2] addition pathway for a variety of silanes and aldehyde/ketone substrates. This preference arises from stronger electrophilicity of the high-valent molybdenum(VI) metal center toward a hydride. Here, we emphasize MoO2Cl2 behaves similar to Lewis acidic trispentafluorophenyl borane B(C6F5)3 in activating Si–H bond.

Does a multiply bonded oxo ligand directly participate in B–H bond activation by a high-valent di-oxo-molybdenum(VI) complex? A density functional theory study

Co-reporter:Liangfang Huang, Jiandi Wang, Xiaoqin Wei and Haiyan Wei

Catalysis Science & Technology 2015 vol. 5(Issue 6) pp:3259-3269

Publication Date(Web):31 Mar 2015

DOI:10.1039/C5CY00177C

The reduction of organic substrates using high-valent oxo-transition metal complexes represents a new catalytic activity. In this study, we theoretically investigated the mechanism of catalytic reduction of amides, amines, nitriles and sulfoxides with boranes by the high-valent di-oxo-molybdenum(VI) complex MoO2Cl2. Our computational results reveal that reduction of sulfoxides with boranes catalyzed by MoO2Cl2 proceeds via a [2 + 2] addition pathway involving the B–H bond of borane adding across the MoO bond to form a metal hydride intermediate, followed by the elimination of the new species HOBcat, accompanied by the loss of the sulfide. The activation free energy of the turnover-limiting step is calculated to be 24.0 kcal mol−1. By contrast, borane additions to either amide, amine or nitrile proceed through an ionic outer-sphere mechanism, in which the substrates attack the boron center to prompt the heterolytic cleavage of the B–H bond, generating an anionic molybdenum(VI) hydride paired with a borylated amide/amine/nitrile cation. Then, the activated organic substrates abstract a hydride from the molybdenum(VI) center to complete the catalytic cycle. The activation free energies of the turnover-limiting step along the ionic outer-sphere pathway are calculated to be ~22.7, 19.7 and 30.6 kcal mol−1 for benzamide, N-(diphenylmethylene)benzenamine, and benzonitrile, respectively. These values are energetically more favorable (~3–8.0 kcal mol−1) than those via the [2 + 2] addition pathway. Along the ionic outer-sphere pathway, the multiply bonded oxo ligand does not participate in the activation of the B–H bond. The ionic outer-sphere mechanism suggests that the high-valent di-oxo-molybdenum(VI) complex MoO2Cl2 acts as a Lewis acid in catalyzing the reduction reaction and activation of B–H bonds.

Mechanistic insights into hydrogen generation for catalytic hydrolysis and alcoholysis of silanes with high-valent oxorhenium(V) complexes

Co-reporter:Wenmin Wang, Jiandi Wang, Liangfang Huang and Haiyan Wei

Catalysis Science & Technology 2015 vol. 5(Issue 4) pp:2157-2166

Publication Date(Web):07 Jan 2015

DOI:10.1039/C4CY01259C

The high-valent oxorhenium(V) complex [Re(O)(hoz)2]+ (1)-catalyzed hydrolytic oxidation of silanes to produce dihydrogen was studied computationally to determine the underlying mechanism. Our results suggested that the oxorhenium(V) complex 1-catalyzed hydrolysis/alcoholysis of silanes proceeds via the ionic out-sphere mechanistic pathway. The turnover-limiting step was found to be the heterolytic cleavage of the Si–H bond and featured a SN2–Si transition state, which corresponds to the nucleophilic anti attack of water or alcohol on the silicon atom in a cis η1-silane rhenium(V) adduct. Dihydrogen was generated upon transferring the hydride from the neutral rhenium hydride [Re(O)(hoz)2H] to the solvated [Me3SiOHR]+ ion. The activation free energy of the turnover-limiting step along the ionic outer-sphere pathway was calculated to be 15.7 kcal mol−1 with water, 15.4 kcal mol−1 with methanol, and 15.9 kcal mol−1 with ethanol. These values are energetically more favorable than the [2 + 2] addition pathway by ~15.0 kcal mol−1. Furthermore, the previously proposed catalytic pathways involving transient rhenium(VII) complexes or via the silicon attack on a rhenium hydroxo/alkoxo complex are shown to possess higher barriers.

A computational study on high-valent mono-oxo-rhenium(V) complex-catalyzed hydrosilylation of carbonyls: What a difference an oxo ligand makes

Co-reporter:Liangfang Huang, Wenmin Wang, Haiyan Wei

Journal of Molecular Catalysis A: Chemical 2015 400() pp: 31-41

Publication Date(Web):

DOI:10.1016/j.molcata.2015.01.019

New Insights into Hydrosilylation of Unsaturated Carbon–Heteroatom (C═O, C═N) Bonds by Rhenium(V)–Dioxo Complexes

Co-reporter:Liangfang Huang, Wenmin Wang, Xiaoqin Wei, and Haiyan Wei

The Journal of Physical Chemistry A 2015 Volume 119(Issue 16) pp:3789-3799

Publication Date(Web):March 31, 2015

DOI:10.1021/acs.jpca.5b00567

The hydrosilylation of unsaturated carbon–heteroatom (C═O, C═N) bonds catalyzed by high-valent rhenium(V)–dioxo complex ReO2I(PPh3)2 (1) were studied computationally to determine the underlying mechanism. Our calculations revealed that the ionic outer-sphere pathway in which the organic substrate attacks the Si center in an η1-silane rhenium adduct to prompt the heterolytic cleavage of the Si–H bond is the most energetically favorable process for rhenium(V)–dioxo complex 1 catalyzed hydrosilylation of imines. The activation energy of the turnover-limiting step was calculated to be 22.8 kcal/mol with phenylmethanimine. This value is energetically more favorable than the [2 + 2] addition pathway by as much as 10.0 kcal/mol. Moreover, the ionic outer-sphere pathway competes with the [2 + 2] addition mechanism for rhenium(V)–dioxo complex 1 catalyzing the hydrosilylation of carbonyl compounds. Furthermore, the electron-donating group on the organic substrates would induce a better activity favoring the ionic outer-sphere mechanistic pathway. These findings highlight the unique features of high-valent transition-metal complexes as Lewis acids in activating the Si–H bond and catalyzing the reduction reactions.

The Unexpected Mechanism Underlying the High-Valent Mono-Oxo-Rhenium(V) Hydride Catalyzed Hydrosilylation of CN Functionalities: Insights from a DFT Study

Co-reporter:Jii Wang;Wenmin Wang;Liangfang Huang; Xiaodi Yang ; Haiyan Wei

ChemPhysChem 2015 Volume 16( Issue 5) pp:1052-1060

Publication Date(Web):

DOI:10.1002/cphc.201402610

Abstract

In this study, we theoretically investigated the mechanism underlying the high-valent mono-oxo-rhenium(V) hydride Re(O)HCl₂(PPh₃)₂ (1) catalyzed hydrosilylation of CN functionalities. Our results suggest that an ionic S_N2-Si outer-sphere pathway involving the heterolytic cleavage of the SiH bond competes with the hydride pathway involving the CN bond inserted into the ReH bond for the rhenium hydride (1) catalyzed hydrosilylation of the less steric CN functionalities (phenylmethanimine, PhCH=NH, and N-phenylbenzylideneimine, PhCH=NPh). The rate-determining free-energy barriers for the ionic outer-sphere pathway are calculated to be ∼28.1 and 27.6 kcal mol⁻¹, respectively. These values are slightly more favorable than those obtained for the hydride pathway (by ∼1–3 kcal mol⁻¹), whereas for the large steric CN functionality of N,1,1-tri(phenyl)methanimine (PhCPh=NPh), the ionic outer-sphere pathway (33.1 kcal mol⁻¹) is more favorable than the hydride pathway by as much as 11.5 kcal mol⁻¹. Along the ionic outer-sphere pathway, neither the multiply bonded oxo ligand nor the inherent hydride moiety participate in the activation of the SiH bond.

Mechanistic Investigation Into Catalytic Hydrosilylation with a High-Valent Ruthenium(VI)–Nitrido Complex: A DFT Study

Co-reporter:Jiandi Wang, Liangfang Huang, Xiaodi Yang, and Haiyan Wei

Organometallics 2015 Volume 34(Issue 1) pp:212-220

Publication Date(Web):December 29, 2014

DOI:10.1021/om501071n

Density functional theory calculations with the B3LYP-D function have been performed to investigate the mechanism of carbonyl hydrosilylation reactions catalyzed by the high-valent nitridoruthenium(VI) complex [RuN(saldach)(CH3OH)]+[ClO4]− (1; saldach is the dianion of racemic N,N′-cyclohexanediylbis(salicylideneimine)). Our computational results indicate a favored ionic outer-sphere mechanistic pathway. This pathway initiates with a silane addition to the RuVI center, which proceeds through a SN2-Si transition state corresponding to the nucleophilic attack of the carbonyl on the silicon center. This attack then prompts the heterolytic cleavage of Si–H bond. The rate-determining energy of the SN2-Si transition state is calculated to be 22.9 kcal/mol with benzaldehyde. In contrast, our calculations indicate that the initial silane addition to the nitrido ligand does not represent an intermediate of the catalytic process leading to the silyl ether products, since it involves high-energy transition states (29.2 and 37.8 kcal/mol) in the reduction of carbonyls. Moreover, the computational results show that the RuIII–saldach species afforded by N–N coupling (with an activation barrier of 24.2 kcal/mol) of the nitridoruthenium(VI) complex provides a competitive hydrosilylation reaction by favoring the ionic outer-sphere mechanistic pathway, associated with a significantly small activation barrier (3.7 kcal/mol). This study provides theoretical insight into the novel properties of the high-valent transition-metal RuVI–nitrido catalyst in catalytic reduction reactions.

Heterolytic cleavage of Si–H bonds: reduction of imines using silane/high-valent oxo-molybdenum MoO2Cl2 as a catalyst

Co-reporter:Yiou Wang, Piao Gu, Wenmin Wang and Haiyan Wei

Catalysis Science & Technology 2014 vol. 4(Issue 1) pp:43-46

Publication Date(Web):31 Oct 2013

DOI:10.1039/C3CY00727H

This work describes a DFT investigation into reducing imines using a high-valent MoO2Cl2/silane system, proposing that a recently introduced mechanistic model, the heterolytic Si–H bond cleavage upon imine substrates attacking the η1-silane molybdenum adduct, accounts for this catalytic reactivity, rather than the [2 + 2] addition mechanism.

Mechanistic insights into B–H bond activation with the high-valent oxo-molybdenum complex MoO2Cl2

Co-reporter:Liangfang Huang and Haiyan Wei

New Journal of Chemistry 2014 vol. 38(Issue 11) pp:5421-5428

Publication Date(Web):01 Sep 2014

DOI:10.1039/C4NJ01188K

The B–H bond activation and the catalytic hydroboration of carbonyl compounds by the high-valent oxo-molybdenum complex MoO2Cl2 were theoretically investigated to determine the underlying mechanism. Our calculation results indicate an unique path – the ionic mechanistic pathway involving the heterolytic cleavage of the B–H bond competes with the [2+2] addition pathway, which involves the addition of the B–H bond across one of the MoO bonds. The rate-determining free energy barriers for the ionic mechanistic pathway are calculated to be 26.9 kcal mol−1, 25.0 kcal mol−1 and 23.7 kcal mol−1 for diphenylketone, benzaldehyde and acetophenone, respectively. These values are energetically slightly favorable than the [2+2] addition mechanism by ∼1–3 kcal mol−1. Furthermore, it is worth noting that the carbonyl compounds bearing the electron donation group will induce a better activity toward the ionic mechanistic pathway.

Role of the Isolable Hydride Intermediate in the Hydrosilylation of Carbonyl Compounds Catalyzed by the High-Valent Mono-OxidoRhenium(V) Complex

Co-reporter:Liangfang Huang;Yu Zhang

European Journal of Inorganic Chemistry 2014 Volume 2014( Issue 33) pp:5714-5723

Publication Date(Web):

DOI:10.1002/ejic.201402464

Abstract

The hydrosilylation of carbonyl compounds catalyzed by high-valent mono-oxido–rhenium(V) complex [Re(O)Cl₃(PPh₃)₂] (1) and its hydride [Re(O)(H)Cl₂(PPh₃)₂] (1H) was theoretically investigated using density functional theory. Our calculations indicated that the most energetically favorable process for 1-catalyzed hydrosilylation was the “ionic mechanistic pathway”. The catalytic cycle is initiated by carbonyl substrate nucleophilic attacks on the η¹-silane rhenium adduct, which results in the heterolytic cleavage of the Si–H bond and generation of a siloxy carbenium ion paired with an anionic rhenium hydride, [ReOCl₃(H)(PPh₃)]^–[Me₃SiOCHPh]⁺. The ionic mechanistic pathway is more favorable than the σ-bond metathesis pathway that involves the generation of rhenium hydride (23.8 versus 31.5 kcal mol^–1). Therefore, our results indicated that an undetected η¹-silane rhenium adduct was the real intermediate rather than the isolable hydride intermediate 1H in the hydrosilylation catalyzed by 1.

Theoretical Study of POCOP-Pincer Iridium(III)/Iron(II) Hydride Catalyzed Hydrosilylation of Carbonyl Compounds: Hydride Not Involved in the Iridium(III) System but Involved in the Iron(II) System

Co-reporter:Wenmin Wang, Piao Gu, Yiou Wang, and Haiyan Wei

Organometallics 2014 Volume 33(Issue 4) pp:847-857

Publication Date(Web):February 10, 2014

DOI:10.1021/om400634w

The catalytic hydrosilylation of carbonyl compounds by two POCOP-pincer transition-metal hydrides, (POCOP)Ir(H)(acetone)+ (1A-acetone) and (POCOP)Fe(H)(PMe3)2 (1B) (POCOP = 2,6-bis(dibutyl-/diisopropylphosphinito)phenyl), was theoretically investigated to determine the underlying reaction mechanism. Several plausible mechanisms were analyzed using density functional theory calculations. The 1A-acetone-catalyzed hydrosilylation of carbonyl compounds proceeds via the ionic hydrosilylation pathway, which is initiated by the nucleophilic attack of the η1-silane metal adduct by carbonyl substrate. This attack results in the heterolytic cleavage of the Si–H bond and the generation of a siloxy carbenium ion paired with a neutral iridium dihydride, [(POCOP)Ir(H)2][R3SiOCHR′]+, followed by transfer of hydride from the metal center to the siloxy carbenium ion to yield the silyl ether product. The activation energy of the turnover-limiting step was calculated as ∼15.2 kcal/mol. This value is energetically more favorable than those of other pathways by as much as 22.6 kcal/mol. The most energetically favorable process for the hydrosilylation of carbonyl compound catalyzed by POCOP-pincer iron hydride 1B was determined as the carbonyl precoordination pathway, which involves the initial coordination of the carbonyl substrate to the metal center and subsequent migratory insertion into the M–H bond to give the alkoxide intermediate. This intermediate then undergoes M–O/Si–H σ-bond metathesis to yield the silyl ether product. The ionic hydrosilylation pathway requires an activation energy that is ∼30.0 kcal/mol higher than that of the carbonyl precoordination pathway. Our calculation results indicate that the hydride moiety is not involved in the POCOP-pincer iridium(III) hydride 1A-acetone-catalyzed hydrosilylation of carbonyl compounds but is involved in the POCOP-pincer iron(II) hydride 1B-catalyzed process.

Cation-Dependent Magnetic Ordering and Room-Temperature Bistability in Azido-Bridged Perovskite-Type Compounds

Co-reporter:Xin-Hua Zhao ; Xing-Cai Huang ; Shao-Liang Zhang ; Dong Shao ; Hai-Yan Wei ;Xin-Yi Wang

Journal of the American Chemical Society 2013 Volume 135(Issue 43) pp:16006-16009

Publication Date(Web):October 16, 2013

DOI:10.1021/ja407654n

A series of end-to-end azido-bridged perovskite-type compounds [(CH3)nNH4–n][Mn(N3)3] (n = 1–4) were synthesized and characterized. Structural phase transitions indicating the general lattice flexibility were observed and confirmed by the crystal structures of different phases. These materials show cation-dependent magnetic ordering at up to 92 K and magnetic bistability near room temperature.

End-On Azido-Bridged 3d–4f Complexes Showing Single-Molecule-Magnet Property

Co-reporter:Xing-Cai Huang, Chun Zhou, Hai-Yan Wei, and Xin-Yi Wang

Inorganic Chemistry 2013 Volume 52(Issue 13) pp:7314-7316

Publication Date(Web):June 7, 2013

DOI:10.1021/ic400986y

Four tetranuclear 3d–4f complexes with the 4f centers bridged solely by end-on azide bridges were reported. The [CuTb]2 compound displays single-molecule-magnet behavior with hysteresis loops observed at up to 2.4 K.

Hydrosilylation of Carbonyls Catalyzed by the Rhenium(V) Oxo Complex [Re(O)(hoz)2]+—A Non-Hydride Pathway

Co-reporter:Piao Gu, Wenmin Wang, Yiou Wang, and Haiyan Wei

Organometallics 2013 Volume 32(Issue 1) pp:47-51

Publication Date(Web):December 19, 2012

DOI:10.1021/om300605j

Catalytic conversion of silane and carbonyls by the cationic rhenium oxo complex [Re(O)(hoz)2]+ (1; hoz = 2-(2′-hydroxyphenyl)-2-oxazoline(1−)) was examined using density functional theory. It is shown that complex 1 catalyzed the carbonyl hydrosilylation via a non-hydride pathway—the ionic hydrogenation mechanism. The complete catalytic cycle is proposed to involve three steps: the formation of cis η1-silane Re(V) adduct, the heterolytic cleavage of a Si–H bond through anti attack of carbonyls at the cis η1-silane Re(V) adduct, and transfers between the rhenium and activated silylcarbonium ion to produce the silyl ether product and regenerate catalyst 1. The σ-bond metathesis like transition state suggested by Abu-Omar, although not located, can be inferred from the ionic hydrogenation transition states (TS_3syn and TS_5syn, in which the carbonyls syn attack the η1-silane Re(V) adduct) associated with the higher energy barrier.

Synthesis of water-soluble phosphonate functionalized single-walled carbon nanotubes and their applications in biosensing

Co-reporter:Pan Li, Hailing Liu, Yu Ding, Yi Wang, Yu Chen, Yiming Zhou, Yawen Tang, Haiyan Wei, Chenxin Cai and Tianhong Lu

Journal of Materials Chemistry A 2012 vol. 22(Issue 30) pp:15370-15378

Publication Date(Web):11 Jun 2012

DOI:10.1039/C2JM31350B

A facile noncovalent approach is proposed to graft phosphonate groups onto the surface of single-walled carbon nanotubes (SWNTs) by π–π stacking interactions between naphthalen-1-ylmethylphosphonic acid (NYPA) and SWNTs. Ultraviolet-visible (UV-vis) spectroscopy, fluorescence spectroscopy, X-ray photoelectron spectroscopy (XPS), fourier transform infrared (FT-IR) spectroscopy and zeta potential analysis confirm the phosphonate groups noncovalently attach on the SWNTs surface, in accordance with the prediction of molecular dynamics (MD) simulations. The phosphonate functionalized SWNTs have good solubility in polar solvent due to the big electrostatic repulsion between phosphonate groups, the strong hydration force of phosphonate groups and the partial debundling of SWNTs. X-ray diffraction (XRD) and Raman spectroscopy measurements demonstrate the water-soluble phosphonate functionalized SWNTs almost completely preserve the electronic and structural integrity of the pristine SWNTs. Meanwhile, the as-prepared phosphonate functionalized SWNTs show good biocompatibility for protein immobilization. Consequently, myoglobin (Mb) proteins immobilized on the phosphonate functionalized SWNTs show excellent bioelectrocatalytic activity towards the reduction of hydrogen peroxide due to the exciting electronic properties of the phosphonate functionalized SWNTs and the fast electron transfer rate of Mb.

Mechanistic insights into hydrogen generation for catalytic hydrolysis and alcoholysis of silanes with high-valent oxorhenium(V) complexes

Co-reporter:Wenmin Wang, Jiandi Wang, Liangfang Huang and Haiyan Wei

Catalysis Science & Technology (2011-Present) 2015 - vol. 5(Issue 4) pp:NaN2166-2166

Publication Date(Web):2015/01/07

DOI:10.1039/C4CY01259C

The high-valent oxorhenium(V) complex [Re(O)(hoz)2]+ (1)-catalyzed hydrolytic oxidation of silanes to produce dihydrogen was studied computationally to determine the underlying mechanism. Our results suggested that the oxorhenium(V) complex 1-catalyzed hydrolysis/alcoholysis of silanes proceeds via the ionic out-sphere mechanistic pathway. The turnover-limiting step was found to be the heterolytic cleavage of the Si–H bond and featured a SN2–Si transition state, which corresponds to the nucleophilic anti attack of water or alcohol on the silicon atom in a cis η1-silane rhenium(V) adduct. Dihydrogen was generated upon transferring the hydride from the neutral rhenium hydride [Re(O)(hoz)2H] to the solvated [Me3SiOHR]+ ion. The activation free energy of the turnover-limiting step along the ionic outer-sphere pathway was calculated to be 15.7 kcal mol−1 with water, 15.4 kcal mol−1 with methanol, and 15.9 kcal mol−1 with ethanol. These values are energetically more favorable than the [2 + 2] addition pathway by ~15.0 kcal mol−1. Furthermore, the previously proposed catalytic pathways involving transient rhenium(VII) complexes or via the silicon attack on a rhenium hydroxo/alkoxo complex are shown to possess higher barriers.

Does a multiply bonded oxo ligand directly participate in B–H bond activation by a high-valent di-oxo-molybdenum(VI) complex? A density functional theory study

Co-reporter:Liangfang Huang, Jiandi Wang, Xiaoqin Wei and Haiyan Wei

Catalysis Science & Technology (2011-Present) 2015 - vol. 5(Issue 6) pp:NaN3269-3269

Publication Date(Web):2015/03/31

DOI:10.1039/C5CY00177C

The reduction of organic substrates using high-valent oxo-transition metal complexes represents a new catalytic activity. In this study, we theoretically investigated the mechanism of catalytic reduction of amides, amines, nitriles and sulfoxides with boranes by the high-valent di-oxo-molybdenum(VI) complex MoO2Cl2. Our computational results reveal that reduction of sulfoxides with boranes catalyzed by MoO2Cl2 proceeds via a [2 + 2] addition pathway involving the B–H bond of borane adding across the MoO bond to form a metal hydride intermediate, followed by the elimination of the new species HOBcat, accompanied by the loss of the sulfide. The activation free energy of the turnover-limiting step is calculated to be 24.0 kcal mol−1. By contrast, borane additions to either amide, amine or nitrile proceed through an ionic outer-sphere mechanism, in which the substrates attack the boron center to prompt the heterolytic cleavage of the B–H bond, generating an anionic molybdenum(VI) hydride paired with a borylated amide/amine/nitrile cation. Then, the activated organic substrates abstract a hydride from the molybdenum(VI) center to complete the catalytic cycle. The activation free energies of the turnover-limiting step along the ionic outer-sphere pathway are calculated to be ~22.7, 19.7 and 30.6 kcal mol−1 for benzamide, N-(diphenylmethylene)benzenamine, and benzonitrile, respectively. These values are energetically more favorable (~3–8.0 kcal mol−1) than those via the [2 + 2] addition pathway. Along the ionic outer-sphere pathway, the multiply bonded oxo ligand does not participate in the activation of the B–H bond. The ionic outer-sphere mechanism suggests that the high-valent di-oxo-molybdenum(VI) complex MoO2Cl2 acts as a Lewis acid in catalyzing the reduction reaction and activation of B–H bonds.

Heterolytic cleavage of Si–H bonds: reduction of imines using silane/high-valent oxo-molybdenum MoO2Cl2 as a catalyst

Co-reporter:Yiou Wang, Piao Gu, Wenmin Wang and Haiyan Wei

Catalysis Science & Technology (2011-Present) 2014 - vol. 4(Issue 1) pp:NaN46-46

Publication Date(Web):2013/10/31

DOI:10.1039/C3CY00727H

This work describes a DFT investigation into reducing imines using a high-valent MoO2Cl2/silane system, proposing that a recently introduced mechanistic model, the heterolytic Si–H bond cleavage upon imine substrates attacking the η1-silane molybdenum adduct, accounts for this catalytic reactivity, rather than the [2 + 2] addition mechanism.

Synthesis of water-soluble phosphonate functionalized single-walled carbon nanotubes and their applications in biosensing

Co-reporter:Pan Li, Hailing Liu, Yu Ding, Yi Wang, Yu Chen, Yiming Zhou, Yawen Tang, Haiyan Wei, Chenxin Cai and Tianhong Lu

Journal of Materials Chemistry A 2012 - vol. 22(Issue 30) pp:NaN15378-15378

Publication Date(Web):2012/06/11

DOI:10.1039/C2JM31350B

A facile noncovalent approach is proposed to graft phosphonate groups onto the surface of single-walled carbon nanotubes (SWNTs) by π–π stacking interactions between naphthalen-1-ylmethylphosphonic acid (NYPA) and SWNTs. Ultraviolet-visible (UV-vis) spectroscopy, fluorescence spectroscopy, X-ray photoelectron spectroscopy (XPS), fourier transform infrared (FT-IR) spectroscopy and zeta potential analysis confirm the phosphonate groups noncovalently attach on the SWNTs surface, in accordance with the prediction of molecular dynamics (MD) simulations. The phosphonate functionalized SWNTs have good solubility in polar solvent due to the big electrostatic repulsion between phosphonate groups, the strong hydration force of phosphonate groups and the partial debundling of SWNTs. X-ray diffraction (XRD) and Raman spectroscopy measurements demonstrate the water-soluble phosphonate functionalized SWNTs almost completely preserve the electronic and structural integrity of the pristine SWNTs. Meanwhile, the as-prepared phosphonate functionalized SWNTs show good biocompatibility for protein immobilization. Consequently, myoglobin (Mb) proteins immobilized on the phosphonate functionalized SWNTs show excellent bioelectrocatalytic activity towards the reduction of hydrogen peroxide due to the exciting electronic properties of the phosphonate functionalized SWNTs and the fast electron transfer rate of Mb.