Mei Wang

Electrocatalytic water oxidation by copper(II) complexes containing a tetra- or pentadentate amine-pyridine ligand

Co-reporter:Junyu Shen;Peili Zhang;Jian Jiang;Licheng Sun

Chemical Communications 2017 vol. 53(Issue 31) pp:4374-4377

Publication Date(Web):2017/04/13

DOI:10.1039/C7CC00332C

Two water soluble copper(II) complexes containing amine-pyridine ligands were found to be catalytically active for water oxidation reactions in basic solutions, with observed rate constants of 13.1–18.7 s−1. These complexes are robust in basic solutions and displayed good stability over 5 h of electrolysis in pH 11.5 phosphate buffer at 1.4 V vs. NHE.

Photocatalytic H2 production using a hybrid assembly of an [FeFe]-hydrogenase model and CdSe quantum dot linked through a thiolato-functionalized cyclodextrin

Co-reporter:Minglun Cheng;Shuai Zhang;Fengyuan Liu;Yong Yang;Boshun Wan;Licheng Sun

Faraday Discussions 2017 (Volume 198) pp:197-209

Publication Date(Web):2017/06/02

DOI:10.1039/C6FD00207B

It is a great challenge to develop iron-based highly-efficient and durable catalytic systems for the hydrogen evolution reaction (HER) by understanding and learning from [FeFe]-hydrogenases. Here we report photocatalytic H2 production by a hybrid assembly of a sulfonate-functionalized [FeFe]-hydrogenase mimic (1) and CdSe quantum dot (QD), which is denoted as 1/β-CD-6-S–CdSe (β-CD-6-SH = 6-mercapto-β-cyclodextrin). In this assembly, thiolato-functionalized β-CD acts not only as a stabilizing reagent of CdSe QDs but also as a host compound for the diiron catalyst, so as to confine CdSe QDs to the space near the site of diiron catalyst. In addition, another two reference systems comprising MAA–CdSe QDs (HMAA = mercaptoacetic acid) and 1 in the presence and absence of β-CD, denoted as 1/β-CD/MAA–CdSe and 1/MAA–CdSe, were studied for photocatalytic H2 evolution. The influences of β-CD and the stabilizing reagent β-CD-6-S− on the stability of diiron catalyst, the fluorescence lifetime of CdSe QDs, the apparent electron transfer rate, and the photocatalytic H2-evolving efficiency were explored by comparative studies of the three hybrid systems. The 1/β-CD-6-S–CdSe system displayed a faster apparent rate for electron transfer from CdSe QDs to the diiron catalyst compared to that observed for MAA–CdSe-based systems. The total TON for visible-light driven H2 evolution by the 1/β-CD-6-S–CdSe QDs in water at pH 4.5 is about 2370, corresponding to a TOF of 150 h−1 in the initial 10 h of illumination, which is 2.7- and 6.6-fold more than the amount of H2 produced from the reference systems 1/β-CD/MAA–CdSe and 1/MAA–CdSe. Additionally, 1/β-CD-6-S–CdSe gave 2.4–5.1 fold enhancement in the apparent quantum yield and significantly improved the stability of the system for photocatalytic H2 evolution.

Low-cost solution-processed digenite Cu9S5 counter electrode for dye-sensitized solar cells

Co-reporter:Maowei Hu;Ze Yu;JiaJia Li;Xiaoqing Jiang;Jianbo Lai;Xichuan Yang;Licheng Sun

RSC Advances (2011-Present) 2017 vol. 7(Issue 61) pp:38452-38457

Publication Date(Web):2017/08/02

DOI:10.1039/C7RA06822K

The development of low-cost alternatives to the commonly used but expensive platinum (Pt) catalyst in dye-sensitized solar cells (DSSCs) is important from a commercial point of view. In this work, Cu9S5 nanocrystalline film is fabricated directly onto a F-doped SnO2 (FTO) substrate by a solution-processed spin-coating method with low temperature post-treatment at 250 °C and it is further explored as a counter electrode (CE) material in DSSCs. The results from cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) disclose that Cu9S5 film exhibits a higher catalytic ability for the state-of-the-art cobalt(II/III) tris(bipyridyl) ([Co(bpy)3]2+/3+) redox system as compared to the widely used iodine-based electrolyte. Consequently, the DSSC devices based on the cobalt complex redox shuttles show a power conversion efficiency (PCE) of 5.7% measured at 100 mW cm−2 illumination (AM 1.5G), which is substantially higher than that of the iodine-based counterpart (3.9%). This has been the first presentation for the application of digenite copper sulfides as an electrocatalyst for the [Co(bpy)3]2+/3+ redox system in DSSCs. The present finding represents a promising solution for the development of alternative cost-effective CE materials for DSSCs in the future.

Visible-light-absorbing semiconductor/molecular catalyst hybrid photoelectrodes for H2 or O2 evolution: recent advances and challenges

Co-reporter:Mei Wang;Yong Yang;Junyu Shen;Jian Jiang;Licheng Sun

Sustainable Energy & Fuels (2017-Present) 2017 vol. 1(Issue 8) pp:1641-1663

Publication Date(Web):2017/09/26

DOI:10.1039/C7SE00222J

The research on the conversion of solar energy and its storage as an eco-friendly and momentarily available chemical fuel, such as H2, by sunlight-driven water splitting is closely related to the sustainable development of the global economy and to the continuous improvement of the modern living standards of human beings. One of the most promising approaches to sunlight-driven water splitting is to construct a dual-illuminated photoelectrochemical (PEC) cell by integrating a photoanode with a photocathode in a tandem configuration. To this end, the important work is to individually develop highly efficient, durable, inexpensive, and readily scalable photoanodes and photocathodes for each half reaction of water splitting, either O2 or H2 evolution reaction (OER or HER). A promising approach emerging in recent years towards OER photoanodes and HER photocathodes is the immobilization of molecular catalysts (MC) onto the surface of visible-light-absorbing semiconductor (VLASC) electrodes. Very recently, some encouraging results have been achieved in the construction of MC-modified VLASC photoanodes and photocathodes. This review is focused on the recent advances in hybrid photoelectrodes for OER and HER, which were built by the integration of MCs with VLASC materials. After a brief introduction of three major units, viz. VLASC materials, MCs, and anchor groups, used to date for fabricating hybrid photoelectrodes for OER and HER, the construction strategy and the performance of the VLASC/MC photoanodes and photocathodes are described in two respective chapters. Finally, challenges and developments in future studies of VLASC/MC hybrid photoelectrodes are discussed.

Highly active and durable electrocatalytic water oxidation by a NiB0.45/NiOx core-shell heterostructured nanoparticulate film

Co-reporter:Jian Jiang, Mei Wang, Wensheng Yan, Xiaofeng Liu, Jinxuan Liu, Jinlong Yang, Licheng Sun

Nano Energy 2017 Volume 38(Volume 38) pp:

Publication Date(Web):1 August 2017

DOI:10.1016/j.nanoen.2017.05.045

•A NiB0.45/NiOx core-shell film was fabricated by a convenient and scalable procedure.•This film displayed superior intrinsic activity for electrocatalytic water oxidation.•The high activity of the film maintains over 60 h of electrolysis in basic solutions.•Good performance stems from the conductive core and active NiOOH at shell surface.On the way to energy-efficient and cost-effective hydrogen production by electrochemical or photoelectrochemical water splitting, it is of primary importance to develop highly active and durable water oxidation electrocatalysts based on earth-abundant elements. Here we report a highly active, robust, cheap, and facilely fabricated O2-evolving catalyst on a Cu foil, NiB0.45-250/Cu, which forms a NiB0.45/NiOx core-shell heterostructured nanoparticulate film during anodic electrolysis. The performance of NiB0.45-250/Cu, to produce 10 mA cm−2 at 296 mV overpotential in 1 M KOH over 60 h, is at par with the best efficiency of earth-abundant electrocatalysts reported to date and surpasses that of IrO2-loaded copper electrode under identical conditions. Experimental evidence and theoretical calculations reveal the correlations of B/Ni atomic ratio and annealing temperature with the morphology, surface microtexture, electrochemical active surface area, and electrical conductivity of NiBx films. Optimal combination of these factors can evidently enhance the catalytic activity of nickel boride electrocatalysts.Download high-res image (361KB)Download full-size image

A Cu-Based Nanoparticulate Film as Super-Active and Robust Catalyst Surpasses Pt for Electrochemical H2 Production from Neutral and Weak Acidic Aqueous Solutions

Co-reporter:Peili Zhang;Hong Chen;Yongqi Liang;Junliang Sun;Licheng Sun

Advanced Energy Materials 2016 Volume 6( Issue 8) pp:

Publication Date(Web):

DOI:10.1002/aenm.201502319

Electrocatalysts that are stable and highly active at low overpotential (η) under mild conditions as well as cost-effective and scalable are eagerly desired for potential use in photo- and electro-driven hydrogen evolution devices. Here the fabrication and characterization of a super-active and robust Cu-Cu_xO-Pt nanoparticulate electrocatalyst is reported, which displays a small Tafel slope (44 mV dec⁻¹) and a large exchange current density (1.601 mA cm⁻²) in neutral buffer solution. The catalytic current density of this catalyst film reaches 500 mA cm⁻² at η = −390 ± 12 mV and 20 mA cm⁻² at η = −45 ± 3 mV, which are significantly higher than the values displayed by Pt foil and Pt/C electrodes in neutral buffer solution and even comparable with the activity of Pt electrode in 0.5 m H₂SO₄ solution.

Evident Enhancement of Photoelectrochemical Hydrogen Production by Electroless Deposition of M-B (M = Ni, Co) Catalysts on Silicon Nanowire Arrays

Co-reporter:Yong Yang, Mei Wang, Peili Zhang, Weihan Wang, Hongxian Han, and Licheng Sun

ACS Applied Materials & Interfaces 2016 Volume 8(Issue 44) pp:30143

Publication Date(Web):October 20, 2016

DOI:10.1021/acsami.6b09600

Modification of p-type Si surface by active and stable earth-abundant electrocatalysts is an effective strategy to improve the sluggish kinetics for the hydrogen evolution reaction (HER) at p-Si/electrolyte interface and to develop highly efficient and low-cost photocathodes for hydrogen production from water. To this end, Si nanowire (Si-NW) array has been loaded with highly efficient electrocatalysts, M-B (M = Ni, Co), by facile and quick electroless plating to build M-B catalyst-modified Si nanowire-array-textured photocathodes for water reduction to H2. Compared with the bare Si-NW array, composite Si-NWs/M-B arrays display evidently enhanced photoelectrochemical (PEC) performance. The onset potential (Vphon) of cathodic photocurrent is positively shifted by 530–540 mV to 0.44–0.45 V vs RHE, and the short-circuit current density (Jsc) is up to 19.5 mA cm–2 in neutral buffer solution under simulated 1 sun illumination. Impressively, the half-cell photopower conversion efficiencies (ηhc) of the optimized Si-NWs/Co–B (2.53%) and Si-NWs/Ni–B (2.45%) are comparable to that of Si-NWs/Pt (2.46%). In terms of the large Jsc, Vphon, and ηhc values, as well as the high Faradaic efficiency, Si-NWs/M-B electrodes are among the top performing Si photocathodes which are modified with HER electrocatalysts but have no buried solid/solid junction.Keywords: cobalt boride; hydrogen evolution reaction; nickel boride; photocathode; photoelectrochemical catalysis; silicon

Effect of Bridgehead Steric Bulk on the Intramolecular C–H Heterolysis of [FeFe]-Hydrogenase Active Site Models Containing a P2N2 Pendant Amine Ligand

Co-reporter:Dehua Zheng; Mei Wang; Ning Wang; Minglun Cheng;Licheng Sun

Inorganic Chemistry 2016 Volume 55(Issue 2) pp:411-418

Publication Date(Web):July 31, 2015

DOI:10.1021/acs.inorgchem.5b00923

A series of pendant amine-containing [FeFe]-hydrogenase models, [X(CH2S-μ)2{Fe(CO)3}{Fe(CO)(P2PhN2Bn)}] (1H, X = CH2; 2Me, C(CH3)2; 3Et, C(CH2CH3)2; and P2PhN2Bn = 1,5-dibenzyl-3,7-diphenyl-1,5-diaza-3,7-diphosphacyclooctane) with different groups at the bridgehead carbon of the S-to-S linker were synthesized. The oxidations of these complexes as well as the reverse reduction reaction were studied by cyclic voltammetry and in situ IR spectroscopy. Regardless of the bridgehead steric bulk, all three complexes demonstrate intramolecular iron-mediated C(sp3)–H bond heterolytic cleavage with the assistance of the pendant amine base within the chelating diphosphine ligand in the two-electron oxidation process. X-ray crystallographic analysis shows that the doubly oxidized products, [1′H]+, [2′Me]+, and [3′Et]+, all have a rigid FeSC three-membered ring at the open apical site of the rotated iron center. The most noticeable difference in structures of the oxidized complexes is that the single CO ligand of the rotated Fe(P2PhN2Bn)(CO) unit in [1′H]+ and [2′Me]+ is found below the Fe···Fe vector, while in [3′Et]+ an unusually rotated Fe(P2PhN2Bn)(CO) moiety positions one of the P donors within the bidentate ligand under the Fe···Fe vector. The starting FeIFeI complexes can be recovered from their corresponding doubly oxidized complexes by reduction in the presence of Brönsted acid.

Electroless plated Ni–Bx films as highly active electrocatalysts for hydrogen production from water over a wide pH range

Co-reporter:Peili Zhang, Mei Wang, Yong Yang, Tianyi Yao, Hongxian Han, Licheng Sun

Nano Energy 2016 Volume 19() pp:98-107

Publication Date(Web):January 2016

DOI:10.1016/j.nanoen.2015.11.020

•NiB0.54 film displays high activity for electrocatalytic H2 evolution in entire pH range.•The current maintains constant over 20 h CPE of NiB0.54 solutions at η=−100 mV.•The B:Ni atomic ratio greatly influences the catalytic H2-evolution property of NiBx.•The fabrication process of such a low-cost electrocatalyst is easily scalable.The performance of electroless plated Ni–Bx films was studied in a wide pH range for the hydrogen evolution reaction (HER). The atomic ratio of B to Ni has great influence on the particle size and the morphology of Ni–Bx materials, and more importantly on the catalytic H2-evolution property of Ni–Bx films. The film with a B:Ni atomic ratio of 0.54, denoted as Ni–B0.54, displayed the best performance with a current density of 10 mA cm−2 at very low overpotentials (η) of 45 mV in 0.5 M H2SO4, 54 mV in 1.0 M pH 7 phosphate buffer solution (PBS), and 135 mV in 1.0 M KOH, and the catalytic activity maintained over 20-h electrolysis at η=100 mV in all tested media of different pH values. The Tafel slopes of the Ni–B0.54 film are 43, 77, and 88 mV dec−1 in 0.5 M H2SO4, 1.0 M neutral PBS, and 1.0 M KOH, respectively. These results show that the combination of earth-abundant nickel and boron elements in an optimal B-to-Ni atomic ratio can provide highly active and stable electrocatalysts for the HER over a wide pH range.The electroless plated Ni-B0.54 film displayed a superior activity for electrochemical H2 production with a current density of 10 mA cm−2 at very low overpotentials (η) of 45 mV in 0.5 M H2SO4, 54 mV in 1.0 M pH 7 PBS, and 135 mV in 1.0 M KOH solution, and the catalytic activity maintained over 20-h electrolysis at η = 100 mV in all tested media of different pH values.

Integration of organometallic complexes with semiconductors and other nanomaterials for photocatalytic H2 production

Co-reporter:Mei Wang, Kai Han, Shuai Zhang, Licheng Sun

Coordination Chemistry Reviews 2015 Volume 287() pp:1-14

Publication Date(Web):15 March 2015

DOI:10.1016/j.ccr.2014.12.005

•Hybrid systems built by integration of the first-row transition metal complexes with inorganic or organic semiconductors for photocatalytic H2 production are surveyed in the review.•The review also includes the photocatalytic H2 production hybrid systems containing an organometallic complex and an inorganic or organic nanomaterial as well as a metal-organic framework (MOF) material.•The mechanisms for the light-driven H2-generation reactions catalyzed by the hybrid systems are presented.The development of energy-efficient, cost-effective and durable photocatalytic systems for water splitting is one of the scientific problems that must be solved before the successful transformation from a fossil fuel-based economy to a solar fuel-based economy can be realized. Conventional photocatalytic systems are generally divided into heterogeneous systems of semiconductors, usually modified by noble metals or inorganic cocatalysts, and homogeneous systems comprised of molecular catalysts and organic or organometallic chromophores. In recent years, some hybrid photocatalytic systems were reported to be highly active and robust for photoinduced H2 production, indicating that the integration of semiconducting materials with proper molecular catalysts is an effective strategy for constructing efficient photocatalytic systems for water splitting. This review will focus on hybrid photocatalytic systems, developed in the past three years, in which proton reduction molecular catalysts incorporate either semiconducting materials or inorganic, metal-organic, and other polymeric nanomaterials for photochemical H2 generation from water. In the last section of the review, problems existing in the current hybrid photocatalytic systems are discussed; future challenges and developments are envisaged.

CdSe quantum dots/molecular cobalt catalyst co-grafted open porous NiO film as a photocathode for visible light driven H2 evolution from neutral water

Co-reporter:Peng Meng, Mei Wang, Yong Yang, Shuai Zhang and Licheng Sun

Journal of Materials Chemistry A 2015 vol. 3(Issue 37) pp:18852-18859

Publication Date(Web):2015/08/20

DOI:10.1039/C5TA06255A

An active noble-metal-free photocathode was fabricated by co-grafting water-soluble thioglycolic acid-stabilized CdSe quantum dots and a molecular cobaloxime catalyst (CoP) through chemical linkage on a p-type open porous NiO film. This photocathode was used as a working electrode in a three-electrode cell, which displayed a photocurrent density up to 110 µA cm−2 at an applied potential of 0 V vs. NHE in 0.1 M Na2SO4 solution at pH 6.8 upon visible light illumination. The comparative studies showed that the open porous NiO/CdSe electrode did display a higher photocurrent density than that exhibited by an analogous planar NiO/CdSe electrode made by doctor-blading a NiO paste. Long-time photoelectrolysis experiments revealed that about 83% of the photocurrent density remained after 3.5 h illumination at −0.2 V vs. NHE. The open porous NiO/CdSe/CoP photocathode showed a considerably better current density and photocatalytic stability compared to the so-far reported dye- or QD-sensitized NiO cathodes with a cobaloxime catalyst chemically attached or physically adsorbed on the electrode surface under similar conditions.

Photochemical hydrogen production from water catalyzed by CdTe quantum dots/molecular cobalt catalyst hybrid systems

Co-reporter:Kai Han, Mei Wang, Shuai Zhang, Suli Wu, Yong Yang and Licheng Sun

Chemical Communications 2015 vol. 51(Issue 32) pp:7008-7011

Publication Date(Web):17 Mar 2015

DOI:10.1039/C5CC00536A

A hybrid system with a coordinative interaction between a cobalt complex of a N2S2-tetradentate ligand and CdTe quantum dots displayed a high activity (initial TOF 850 h−1) and improved stability (TON 1.44 × 104 based on catalyst over 30 h) for the photochemical H2 generation from water, with a quantum efficiency of 5.32% at 400 nm.

A super-efficient cobalt catalyst for electrochemical hydrogen production from neutral water with 80 mV overpotential

Co-reporter:Lin Chen, Mei Wang, Kai Han, Peili Zhang, Frederic Gloaguen and Licheng Sun

Energy & Environmental Science 2014 vol. 7(Issue 1) pp:329-334

Publication Date(Web):22 Oct 2013

DOI:10.1039/C3EE42194E

Self-assembled molecular iron and cobalt catalysts (MP4N2, M = Fe, Co) bearing a multihydroxy-functionalized tetraphosphine ligand electrocatalyze H2 generation from neutral water on a mercury electrode at −1.03 and −0.50 V vs. NHE, respectively. Complex CoP4N2 displays extremely low overpotential (Eonset = 80 mV) while maintaining high activity and good stability. Bulk electrolysis of CoP4N2 in a neutral phosphate buffer solution at −1.0 V vs. NHE produced 9.24 × 104 mol H2 per mol cat. over 20 h, with a Faradaic efficiency close to 100% and without apparent deactivation.

Intramolecular Iron-Mediated C–H Bond Heterolysis with an Assist of Pendant Base in a [FeFe]-Hydrogenase Model

Co-reporter:Dehua Zheng ; Ning Wang ; Mei Wang ; Shengda Ding ; Chengbing Ma ; Marcetta Y. Darensbourg ; Michael B. Hall ;Licheng Sun

Journal of the American Chemical Society 2014 Volume 136(Issue 48) pp:16817-16823

Publication Date(Web):September 22, 2014

DOI:10.1021/ja5078014

Although many metalloenzymes containing iron play a prominent role in biological C–H activation processes, to date iron-mediated C(sp3)–H heterolysis has not been reported for synthetic models of Fe/S-metalloenzymes. In contrast, ample precedent has established that nature’s design for reversible hydrogen activation by the diiron hydrogenase ([FeFe]-H2ase) active site involves multiple irons, sulfur bridges, a redox switch, and a pendant amine base, in an intricate arrangement to perform H–H heterolytic cleavage. In response to whether this strategy might be extended to C–H activation, we report that a [FeFe]-H2ase model demonstrates iron-mediated intramolecular C–H heterolytic cleavage via an agostic C–H interaction, with proton removal by a nearby pendant amine, affording FeII–[Fe′II–CH–S] three-membered-ring products, which can be reduced back to 1 by Cp2Co in the presence of HBF4. The function of the pendant base as a proton shuttle was confirmed by the crystal structures of the N-protonated intermediate and the final deprotonated product in comparison with that of a similar but pendant-amine-free complex that does not show evidence of C–H activation. The mechanism of the process was backed up by DFT calculations.

The influence of a S-to-S bridge in diiron dithiolate models on the oxidation reaction: a mimic of the Hairox state of [FeFe]-hydrogenases

Co-reporter:Dehua Zheng, Mei Wang, Lin Chen, Ning Wang, Minglun Cheng and Licheng Sun

Chemical Communications 2014 vol. 50(Issue 66) pp:9255-9258

Publication Date(Web):05 Jun 2014

DOI:10.1039/C4CC03583F

Two-electron oxidation of a diiron complex (1) containing a bulky S-to-S bridge with an exocyclic carbonyl group affords [1(OH)]+, which replicates the coordination structure and electronic configuration of Hairox, and the chemically reversible reaction between 1 and [1(OH)]+ mimics the bioprocess of interconversion of the inactive Hairox and the active Hred states of the [FeFe]-hydrogenases.

Highly efficient molecular nickel catalysts for electrochemical hydrogen production from neutral water

Co-reporter:Peili Zhang, Mei Wang, Yong Yang, Dehua Zheng, Kai Han and Licheng Sun

Chemical Communications 2014 vol. 50(Issue 91) pp:14153-14156

Publication Date(Web):22 Sep 2014

DOI:10.1039/C4CC05511J

A series of nickel complexes containing N5-pentadentate ligands with different amine-to-pyridine ratios were studied for electrochemical H2 production in neutral water and the one with a diamine–tripyridine ligand displays a TON of up to 308000 over 60 h electrolysis at −1.25 V vs. SHE, with a Faradaic efficiency of ∼91%.

Redox Reactions of [FeFe]-Hydrogenase Models Containing an Internal Amine and a Pendant Phosphine

Co-reporter:Dehua Zheng, Mei Wang, Lin Chen, Ning Wang, and Licheng Sun

Inorganic Chemistry 2014 Volume 53(Issue 3) pp:1555-1561

Publication Date(Web):January 14, 2014

DOI:10.1021/ic4025519

A diiron dithiolate complex with a pendant phosphine coordinated to one of the iron centers, [(μ-SCH2)2N(CH2C6H4-o-PPh2){Fe2(CO)5}] (1), was prepared and structurally characterized. The pendant phosphine is dissociated together with a CO ligand in the presence of excess PMe3, to afford [(μ-SCH2)2N(CH2C6H4-o-PPh2){Fe(CO)2(PMe3)}2] (2). Redox reactions of 2 and related complexes were studied in detail by in situ IR spectroscopy. A series of new FeIIFeI ([3]+ and [6]+), FeIIFeII ([4]2+), and FeIFeI (5) complexes relevant to Hox, HoxCO, and Hred states of the [FeFe]-hydrogenase active site were detected. Among these complexes, the molecular structures of the diferrous complex [4]2+ with the internal amine and the pendant phosphine co-coordinated to the same iron center and the triphosphine diiron complex 5 were determined by X-ray crystallography. To make a comparison, the redox reactions of an analogous complex, [(μ-SCH2)2N(CH2C6H5){Fe(CO)2(PMe3)}2] (7), were also investigated by in situ IR spectroscopy in the absence or presence of extrinsic PPh3, which has no influence on the oxidation reaction of 7. The pendant phosphine in the second coordination sphere makes the redox reaction of 2 different from that of its analogue 7.

Nickel Complex with Internal Bases as Efficient Molecular Catalyst for Photochemical H2 Production

Co-reporter:Yong Yang; Mei Wang;Liqin Xue;Fengbo Zhang;Lin Chen;Dr. Mårten S. G. Ahlquist; Licheng Sun

ChemSusChem 2014 Volume 7( Issue 10) pp:2889-2897

Publication Date(Web):

DOI:10.1002/cssc.201402381

Abstract

A Ni complex with internal bases that contain bipyridine-derived ligands, [Ni(L)₂(H₂O)₂](BF₄)₂ ([1](BF₄)₂, L=2-(2-pyridyl)-1,8-naphthyridine), and a reference complex that bears analogous bipyridine-derived ligands but without an internal base, [Ni(L′)₃](BF₄)₂ ([2](BF₄)₂, L′=2-(2-pyridyl)quinoline), were synthesized and characterized. The electrochemical properties of these complexes were studied in CH₃CN, H₂O, and a mixture of EtOH/H₂O. The fluorescence spectroscopic studies suggest that both dynamic and the sphere-of-action static quenching exist in the fluorescein Fl²⁻/[1]²⁺ and Fl²⁻/[2]²⁺ systems. These noble-metal-free molecular systems were studied for photocatalytic H₂ generation. Under optimal conditions, the turnover number of H₂ evolution reaches 3230 based on [1]²⁺, whereas [2]²⁺ displays only approximately one third of the turnover of [1]²⁺. A plausible mechanism for the catalytic H₂ generation by [1]²⁺ is presented based on DFT calculations.

A Molecular Copper Catalyst for Electrochemical Water Reduction with a Large Hydrogen-Generation Rate Constant in Aqueous Solution

Co-reporter:Peili Zhang; Mei Wang;Yong Yang;Tianyi Yao; Licheng Sun

Angewandte Chemie 2014 Volume 126( Issue 50) pp:14023-14027

Publication Date(Web):

DOI:10.1002/ange.201408266

Abstract

The copper complex [(bztpen)Cu](BF₄)₂ (bztpen=N-benzyl-N,N′,N′-tris(pyridin-2-ylmethyl)ethylenediamine) displays high catalytic activity for electrochemical proton reduction in acidic aqueous solutions, with a calculated hydrogen-generation rate constant (k_obs) of over 10000 s⁻¹. A turnover frequency (TOF) of 7000 h⁻¹ cm⁻² and a Faradaic efficiency of 96 % were obtained from a controlled potential electrolysis (CPE) experiment with [(bztpen)Cu]²⁺ in pH 2.5 buffer solution at −0.90 V versus the standard hydrogen electrode (SHE) over two hours using a glassy carbon electrode. A mechanism involving two proton-coupled reduction steps was proposed for the dihydrogen generation reaction catalyzed by [(bztpen)Cu]²⁺.

A Molecular Copper Catalyst for Electrochemical Water Reduction with a Large Hydrogen-Generation Rate Constant in Aqueous Solution

Co-reporter:Peili Zhang; Mei Wang;Yong Yang;Tianyi Yao; Licheng Sun

Angewandte Chemie International Edition 2014 Volume 53( Issue 50) pp:13803-13807

Publication Date(Web):

DOI:10.1002/anie.201408266

Abstract

The copper complex [(bztpen)Cu](BF₄)₂ (bztpen=N-benzyl-N,N′,N′-tris(pyridin-2-ylmethyl)ethylenediamine) displays high catalytic activity for electrochemical proton reduction in acidic aqueous solutions, with a calculated hydrogen-generation rate constant (k_obs) of over 10000 s⁻¹. A turnover frequency (TOF) of 7000 h⁻¹ cm⁻² and a Faradaic efficiency of 96 % were obtained from a controlled potential electrolysis (CPE) experiment with [(bztpen)Cu]²⁺ in pH 2.5 buffer solution at −0.90 V versus the standard hydrogen electrode (SHE) over two hours using a glassy carbon electrode. A mechanism involving two proton-coupled reduction steps was proposed for the dihydrogen generation reaction catalyzed by [(bztpen)Cu]²⁺.

Catalytic Activation of H2 under Mild Conditions by an [FeFe]-Hydrogenase Model via an Active μ-Hydride Species

Co-reporter:Ning Wang ; Mei Wang ; Ying Wang ; Dehua Zheng ; Hongxian Han ; Mårten S. G. Ahlquist ;Licheng Sun

Journal of the American Chemical Society 2013 Volume 135(Issue 37) pp:13688-13691

Publication Date(Web):September 3, 2013

DOI:10.1021/ja408376t

A [FeFe]-hydrogenase model (1) containing a chelating diphosphine ligand with a pendant amine was readily oxidized by Fc+ (Fc = Cp2Fe) to a FeIIFeI complex ([1]+), which was isolated at room temperature. The structure of [1]+ with a semibridging CO and a vacant apical site was determined by X-ray crystallography. Complex [1]+ catalytically activates H2 at 1 atm at 25 °C in the presence of excess Fc+ and P(o-tol)3. More interestingly, the catalytic activity of [1]+ for H2 oxidation remains unchanged in the presence of ca. 2% CO. A computational study of the reaction mechanism showed that the most favorable activation free energy involves a rotation of the bridging CO to an apical position followed by activation of H2 with the help of the internal amine to give a bridging hydride intermediate.

Electrocatalytic hydrogen evolution from neutral water by molecular cobalt tripyridine–diamine complexes

Co-reporter:Peili Zhang, Mei Wang, Frederic Gloaguen, Lin Chen, François Quentel and Licheng Sun

Chemical Communications 2013 vol. 49(Issue 82) pp:9455-9457

Publication Date(Web):08 Jul 2013

DOI:10.1039/C3CC43491E

A cobalt complex with a tripyridine–diamine pentadentate ligand was found to be a highly active catalyst for electrochemical H2 production from neutral water, with an activity of 860 mol H2 (mol cat)−1 h−1 (cm2 Hg)−1 over 60 h CPE experiment at −1.25 V in a pH 7 phosphate buffer solution, without considerable deactivation.

Tetranuclear Iron Complexes Bearing Benzenetetrathiolate Bridges as Four-Electron Transformation Templates and Their Electrocatalytic Properties for Proton Reduction

Co-reporter:Lin Chen, Mei Wang, Frederic Gloaguen, Dehua Zheng, Peili Zhang, and Licheng Sun

Inorganic Chemistry 2013 Volume 52(Issue 4) pp:1798-1806

Publication Date(Web):January 31, 2013

DOI:10.1021/ic301647u

Two tetranuclear iron–sulfur complexes, (μ,μ-pbtt)[Fe2(CO)6]2 (pbtt = benzene-1,2,4,5-tetrathiolato, 3) and (μ,μ-obtt)[Fe2(CO)6]2 (obtt = benzene-1,2,3,4-tetrathiolato, 4), were prepared from reaction of Fe3(CO)12 and the corresponding tetramercaptobenzene in THF, respectively. Complexes 5 and 6, (μ,μ-pbtt)[Fe2(CO)5L1][Fe2(CO)5L2] (L1 = CO, L2 = PPyr3 (Pyr = N-pyrrolyl), 5; L1 = L2 = PPyr3, 6) were obtained by controlling CO displacement of 3 with PPyr3. Molecular structures of 3–6 were determined by spectroscopic and single-crystal X-ray analyses. All-CO Fe4S4 complexes 3 and 4 each display four-electron reduction processes in consecutive chemically reversible two-electron reduction events with relatively narrow potential spans in the cyclic voltammograms. Phosphine-substituted Fe4S4 complexes 5 and 6 exhibit two consecutive two-electron reduction events, which are not fully reversible. The electrocatalytic properties of 3 and 4 for proton reduction were studied using a series of carboxylic acids of increasing strength (CH3COOH, CH2ClCOOH, CHCl2COOH, CCl3COOH, and CF3COOH). The mechanisms for electrochemical proton reduction to hydrogen catalyzed by complex 3 as a function of acid strength are discussed.

Recent progress in electrochemical hydrogen production with earth-abundant metal complexes as catalysts

Co-reporter:Mei Wang, Lin Chen and Licheng Sun

Energy & Environmental Science 2012 vol. 5(Issue 5) pp:6763-6778

Publication Date(Web):20 Feb 2012

DOI:10.1039/C2EE03309G

This perspective article reviews the recent important progress in electrocatalytic hydrogen production catalyzed by earth-abundant metal complexes. The catalysts are divided into two categories depending on the media used in the hydrogen-evolving reactions, with an emphasis on the types of acids employed. The catalysts used in the first category, which work in organic solutions, include nickel and cobalt complexes with base-containing diphosphine ligands, cobaloximes, cobalt tetrapyridine complexs, and [NiFe]- and [FeFe]-hydrogenase mimics. Molybdenum and cobalt pentapyridine complexes, as well as the cobalt bis(iminopyridine) complex reported very recently, are the most important examples of catalysts used in the second category, which work in aqueous solutions. The advantages and disadvantages of the different types of catalysts are discussed and the hydrogen-evolving mechanisms for the well-studied catalysts are illustrated. In addition, several molecular catalyst-modified electrodes for hydrogen production are described.

Photocatalytic H2 production in aqueous solution with host-guest inclusions formed by insertion of an FeFe-hydrogenase mimic and an organic dye into cyclodextrins

Co-reporter:Xueqiang Li, Mei Wang, Dehua Zheng, Kai Han, Jingfeng Dong and Licheng Sun

Energy & Environmental Science 2012 vol. 5(Issue 8) pp:8220-8224

Publication Date(Web):21 Jun 2012

DOI:10.1039/C2EE22109H

Bio-inspired noble-metal-free supramolecular systems were constructed by host-guest inclusions of an FeFe-hydrogenase mimic and an organic dye into cyclodextrins respectively, which give typically a ninefold increase in the TON, a sixteenfold enhancement in the quantum efficiency, and a threefold extension in lifetime as compared to the same system in the absence of cyclodextrin for photocatalytic H2 production in aqueous solution.

Phosphine Coordination to a Cobalt Diimine–Dioxime Catalyst Increases Stability during Light-Driven H2 Production

Co-reporter:Pan Zhang ; Pierre-André Jacques ; Murielle Chavarot-Kerlidou ; Mei Wang ; Licheng Sun ; Marc Fontecave ;Vincent Artero

Inorganic Chemistry 2012 Volume 51(Issue 4) pp:2115-2120

Publication Date(Web):February 7, 2012

DOI:10.1021/ic2019132

The combination of cobalt diimine–dioxime complexes with a cyclometalated iridium photosensitizer gives efficient systems for hydrogen generation under visible-light irradiation using triethylamine as a sacrificial electron donor. Interestingly, the addition of triphenylphosphine (PPh3) to the medium results in a significant improvement of the stability of the system, with up to ∼700 turnovers achieved within 10 h. UV–visible spectroscopic monitoring of the reaction allows identification of a PPh3-coordinated CoI intermediate as the active species. Mechanistic issues regarding (i) the photogeneration of the CoI species, (ii) the nature of the active species, and (iii) the influence of PPh3 on the H2-evolution mechanism are discussed.

Multielectron-Transfer Templates via Consecutive Two-Electron Transformations: IronSulfur Complexes Relevant to Biological Enzymes

Co-reporter:Lin Chen; Mei Wang;Dr. Frédéric Gloaguen;Dehua Zheng;Peili Zhang; Licheng Sun

Chemistry - A European Journal 2012 Volume 18( Issue 44) pp:13968-13973

Publication Date(Web):

DOI:10.1002/chem.201201326

Simple Nickel-Based Catalyst Systems Combined With Graphitic Carbon Nitride for Stable Photocatalytic Hydrogen Production in Water

Co-reporter:Jingfeng Dong; Mei Wang;Xueqiang Li;Lin Chen;Yu He; Licheng Sun

ChemSusChem 2012 Volume 5( Issue 11) pp:2133-2138

Publication Date(Web):

DOI:10.1002/cssc.201200490

Photocatalytic Water Reduction and Study of the Formation of FeIFe0 Species in Diiron Catalyst Sytems

Co-reporter:Xueqiang Li; Mei Wang;Lin Chen;Xiuna Wang;Jingfeng Dong; Licheng Sun

ChemSusChem 2012 Volume 5( Issue 5) pp:913-919

Publication Date(Web):

DOI:10.1002/cssc.201100490

Abstract

Noble-metal-free systems with bio-inspired diiron dithiolate mimics of the [FeFe]-hydrogenase active site, namely, [(μ-pdt)Fe₂(CO)₅L] [pdt=propanedithiolate; L=P(CH₂OH)₃ (1), P(CH₃)₃ (2)], as water reduction catalysts with xanthene dyes as photosensitizers and triethylamine as a sacrificial electron donor were studied for visible-light-driven water reduction to hydrogen. These systems display good catalytic activities with the efficiencies in hydrogen evolution of up to 226 turnovers for 1, if Eosin Y was used as the photosensitizer in an environmentally benign solvent (EtOH/H₂O) after 15 h of irradiation (λ>450 nm) under optimal conditions. Under all of the conditions adopted, 1 that has a water soluble phosphine ligand, P(CH₂OH)₃ displayed a higher efficiency than 2, which bears a PMe₃ ligand. The photoinduced electron transfer in the systems was studied using fluorescence, transient absorption, time-resolved UV/Vis, and in situ electron paramagnetic resonance (EPR) spectroscopy. A new electron-transfer mechanism is proposed for hydrogen evolution by these iron-based photocatalytic systems.

Polymerization of rac-lactide catalyzed by group 4 metal complexes containing chiral N atoms

Co-reporter:Minggang Hu;Peili Zhang;Kun Jin;Yuee Chen;Licheng Sun

Polymer Bulletin 2012 Volume 68( Issue 7) pp:1789-1799

Publication Date(Web):2012 April

DOI:10.1007/s00289-011-0647-0

The hydroxyl- and phenoxy-bridged dinuclear zirconium and hafnium complexes, 1 and 2, containing a chiral N atom in the N2O2 ligand (H2L = 2-(((2-pyridylmethyl)(2-hydroxyphenyl)amino)methyl)-4,6-di(tert-butyl)phenol) were used as catalysts for the ring-opening polymerization of rac-lactide. Experiments prove that 1 and 2 are living and controlled catalytic systems with activity up to 3.25 gpol mmolini−1 h−1. The isotactic-rich polylactides in a narrow polydispersity (Mw/Mn = 1.01–1.13) were produced with enantiomeric complexes 1 and 2 (Pm = 0.65–0.73). The kinetic studies show a first-order dependency in both monomer and initiator. The initiation mechanism is discussed on the basis of the MALDI-TOF MS and 1H NMR spectra of the rac-LA oligomer prepared by 1.

Photochemical hydrogen production with molecular devices comprising a zinc porphyrin and a cobaloxime catalyst

Co-reporter:Pan Zhang;XueQiang Li;HongGuang Cui;JingFeng Dong

Science China Chemistry 2012 Volume 55( Issue 7) pp:1274-1282

Publication Date(Web):2012 July

DOI:10.1007/s11426-012-4514-0

Two new noble-metal-free molecular devices, [{Co(dmgH)2Cl}{Zn(PyTPP)}] (1, dmgH = dimethyloxime, PyTPP = 5-(4-pyridyl)-10,15,20-triphenylporphyrin) and [{Co(dmgH)2Cl}{Zn(apPyTPP)}] (2, apPyTPP = 5-[4-(isonicotinamidyl)phenyl]-10,15,20-triphenylporphyrin), for light-driven hydrogen generation were prepared and spectroscopically characterized. The zinc porphyrin photosensitizer and the CoIII-based catalyst unit are linked by axial coordination of a pyridyl group in the periphery of zinc-porphyrin to the cobalt centre of catalyst with different lengths of bridges. The apparent fluorescence quenching and lifetime decays of 1 and 2 were observed in comparison with their reference chromophores, Zn(PyTPP) (3) and Zn(apPyTPP) (4), suggesting a possibility for an intramolecular electron transfer from the singlet excited state of zinc porphyrin unit to the cobalt centre in the molecular devices. Photochemical H2-evolving studies show that complexes 1 and 2 are efficient molecular photocatalysts for visible light-driven H2 generation from water with triethylamine as a sacrificial electron donor in THF/H2O, with turnover numbers up to 46 and 35 for 1 and 2, respectively. In contrast to these molecular devices, the multicomponent catalyst of zinc porphyrin and [Co(dmgH)2PyCl] did not show any fluorescence quenching and as a consequence, no H2 gas was detected by GC analysis in the presence of triethylamine with irradiation of visible light. The plausible mechanism for the photochemical H2 generation with these molecular devices is discussed.

Asymmetric oxidation of sulfides with H2O2 catalyzed by titanium complexes of Schiff bases bearing a dicumenyl salicylidenyl unit

Co-reporter:Ying Wang;Lin Wang;Yu Wang;Xiuna Wang;Licheng Sun

Applied Organometallic Chemistry 2011 Volume 25( Issue 5) pp:325-330

Publication Date(Web):

DOI:10.1002/aoc.1762

Abstract

The sterically hindered Schiff bases (L³–L⁵), prepared from 3,5-dicumenyl salicylaldehyde and chiral amino alcohols, were used in combination with Ti(OiPr)₄ for asymmetric oxidation of aryl methyl sulfides with H₂O₂ as terminal oxidant. Among the ligands L³–L⁵, L⁴ with a tert-butyl group in the chiral carbon of the amino alcohol moiety gave the best result with 89% yield and 73% ee for the sulfoxidation of thioanisole under optimal conditions [with 1 mol% of Ti(OiPr)₄ in a molar ratio of 100:1:1.2:120 for sulfide:Ti(OiPr)₄:ligand:H₂O₂ in CH₂Cl₂ at 0 °C for 3 h]. The reaction afforded good yield (84%) with a moderate enantioselectivity (62% ee) even with a lower catalyst loading from 1.0 to 0.5 mol%. The oxidations of methyl 4-bromophenyl sulfide and methyl 4-methoxyphenyl sulfide with H₂O₂ catalyzed by the Ti(OiPr)₄–L⁴ system gave 79–84% yields and 54–59% ee of the corresponding sulfoxides in CH₂Cl₂ at 20 °C. The chiral induction capability of the cumenyl-modified sterically hindered Schiff bases for sulfoxidation was compared with the conventional Schiff bases bearing tert-butyl groups at the 3,5-positions of the salicylidenyl unit. Copyright © 2011 John Wiley & Sons, Ltd.

Promoting Effect of Electrostatic Interaction between a Cobalt Catalyst and a Xanthene Dye on Visible-Light-Driven Electron Transfer and Hydrogen Production

Co-reporter:Jingfeng Dong ; Mei Wang ; Pan Zhang ; Songqiu Yang ; Jianyong Liu ; Xueqiang Li ;Licheng Sun

The Journal of Physical Chemistry C 2011 Volume 115(Issue 30) pp:15089-15096

Publication Date(Web):June 29, 2011

DOI:10.1021/jp2040778

The readily obtained noble-metal-free molecular catalyst systems, with xanthene dyes (Rose Bengal, RB2–; Eosin Y, EY2–; and Eosin B, EB2–) as photosensitizers, [Co(bpy)3]Cl2 as catalyst, and triethylamine as sacrificial electron donor, are highly active for visible-light-driven (λ > 450 nm) hydrogen production from water. The turnover frequency is up to 54 TON/min versus RB2– with a RB2–/[Co(bpy)3]Cl2 molar ratio of 1:10 in CH3CN/H2O under optimal conditions in the first half hour of irradiation (λ > 450 nm), and the turnover number is up to 2076 versus RB2–. Comparative studies show the following: (1) The photocatalytic H2-evolving activity of the cationic cobalt complex [Co(bpy)3]Cl2 is apparently higher than the neutral cobaloxime complexes with xanthene dyes as potosensitizers, and also much higher than the analogous system of [Ru(bpy)3]Cl2/[Co(bpy)3]Cl2. (2) The UV–vis absorptions of xanthene dyes are red-shifted to different extents upon addition of [Co(bpy)3]Cl2 to the aqueous or CH3CN/H2O solutions of these dyes, while no change was observed in the UV–vis absorptions of photosensitizer with addition of the cobaloximes to the aqueous solution of RB2– or addition of [Co(bpy)3]Cl2 to the aqueous solution of [Ru(bpy)3]Cl2. (3) The fluorescence of RB2– is significantly quenched by [Co(bpy)3]Cl2, but not by the cobaloximes. These special performances of [Co(bpy)3]Cl2 are attributed to the electrostatically attractive interaction between the anionic organic dyes and the cationic cobalt catalyst. The probable mechanism for photoinduced hydrogen production catalyzed by the system of RB2–, [Co(bpy)3]Cl2, and triethylamine is discussed in detail on the basis of fluorescence and transient absorption spectroscopic studies.

Photochemical H2 production with noble-metal-free molecular devices comprising a porphyrin photosensitizer and a cobaloxime catalyst

Co-reporter:Pan Zhang, Mei Wang, Caixia Li, Xueqiang Li, Jingfeng Dong and Licheng Sun

Chemical Communications 2010 vol. 46(Issue 46) pp:8806-8808

Publication Date(Web):19 Oct 2010

DOI:10.1039/C0CC03154B

Among three noble-metal-free molecular devices (1–3) containing a porphyrin photosensitizer and a cobaloxime catalyst, the one with a zinc porphyrin unit displayed apparently higher efficiency for photoinduced H2 production than complex 2 with a magnesium porphyrin and 3 with a free-base porphyrin, possibly due to the formation of a TEA⋯ZnPor–Co triad in solution.

Homogeneous photocatalytic production of hydrogen from water by a bioinspired [Fe2S2] catalyst with high turnover numbers

Co-reporter:Pan Zhang, Mei Wang, Yong Na, Xueqiang Li, Yi Jiang and Licheng Sun

Dalton Transactions 2010 vol. 39(Issue 5) pp:1204-1206

Publication Date(Web):24 Nov 2009

DOI:10.1039/B923159P

A three-component homogeneous catalyst system, composed of a cyclometalated iridium(III) photosensitizer, a bioinspired diiron complex, and TEA in aqueous acetone, proved to be catalytically active for photoinduced H2 production, with up to 660 turnovers over 8 h of irradiation.

Preparation and structures of enantiomeric dinuclear zirconium and hafnium complexes containing two homochiral N atoms, and their catalytic property for polymerization of rac-lactide

Co-reporter:Minggang Hu, Mei Wang, Hongjun Zhu, Lu Zhang, Hui Zhang and Licheng Sun

Dalton Transactions 2010 vol. 39(Issue 18) pp:4440-4446

Publication Date(Web):31 Mar 2010

DOI:10.1039/C001148G

The hydroxy- and phenoxy-bridged dinuclear zirconium and hafnium complexes 2 and 3 of an amine-pyridine-bis(phenolate) ligand (H2L) were prepared from the reaction of Na2L and ZrCl4 in the presence of 0.5 equiv of water in THF, while the reaction of H2L with NaH and then with ZrCl4 in the freshly distilled THF gave an eight-coordinate bis(homoleptic) mononuclear complex L2Zr (1). Two homochiral N atoms were created in each complex upon coordination of the unsymmetric tertiary amine ligands to the metal centers. Enantiomeric dinuclear complexes 2 and 3 both undergo spontaneous resolution during crystallization. The molecular structure of each enantiomer of 2 and 3, as well as the structure of 1, was determined by X-ray analysis and the circular dichroism spectra of N(R)N(R)-2 and N(S)N(S)-2 were studied. The racemates of 2 and 3 catalyzed controlled polymerization of rac-lactide in terms of the linearity of molecular weight versus conversion, forming isotactic-rich polylactide in high yields with a narrow polydispersity.

Preparation and structure of an enantiomeric water-bridged dinuclear indium complex containing two homochiral N atoms and its performance as an initiator in polymerization of rac-lactide

Co-reporter:Minggang Hu, Mei Wang, Peili Zhang, Lin Wang, Fangjun Zhu, Licheng Sun

Inorganic Chemistry Communications 2010 Volume 13(Issue 8) pp:968-971

Publication Date(Web):August 2010

DOI:10.1016/j.inoche.2010.05.009

A novel dinuclear indium complex (1) containing a sole water bridge was prepared from the reaction of InCl3 with an unsymmetric N2O2-ligand and the molecular structure of the complex 1 was determined. The X-ray crystallography data show that the dinuclear complex possesses two homochiral N atoms, namely, N(R)N(R) and N(S)N(S) enantiomers. Complex 1 was used as initiator for ring-opening polymerization of rac-lactide, giving heterotactic-rich polylactide (Pr = 0.63–0.69) with narrow polydispersities (1.13–1.31).An enantiomeric water-bridged dinuclear indium complex (1) containing two homochiral N atoms was prepared and structurally characterized. The racemate of 1 is catalytically active for the ring-opening polymerization of rac-LA, giving heterotactic-rich polylactide with narrow polydispersities.

Photocatalytic Hydrogen Production from Water by Noble-Metal-Free Molecular Catalyst Systems Containing Rose Bengal and the Cobaloximes of BFx-Bridged Oxime Ligands

Co-reporter:Pan Zhang, Mei Wang, Jingfeng Dong, Xueqiang Li, Feng Wang, Lizhu Wu, and Licheng Sun

The Journal of Physical Chemistry C 2010 Volume 114(Issue 37) pp:15868-15874

Publication Date(Web):2017-2-22

DOI:10.1021/jp106512a

Hydrogen evolution was observed from the noble-metal-free catalyst systems, comprising Rose Bengal, BFx-bridged cobaloximes, and triethylamine, in an aqueous solution under irradiation of visible light. Two types of BFx-bridged cobaloximes—namely, the annulated cobaloximes [Co(dmgBF2)2(H2O)2] (1, dmgBF2 = (difluoroboryl)dimethylglyoximate anion) and [Co(dpgBF2)2(H2O)2] (2, dpgBF2 = (difluoroboryl)diphenylglyoximate anion), and the clathrochelated cobaloximes [Co(dmg(BF)2/3)3](BF4) (3) and [Co(dpg(BF)2/3)3](BF4) (4)—were used as catalysts. Among the four cobalt complexes, complex 1 displayed the highest hydrogen-evolving efficiency, with turnovers up to 327. Complexes 2 and 4 that bear the diphenylglyoximate ligands exhibited much lower efficiencies as compared with their analogues 1 and 3 that have the dimethylglyoximate ligands. The hydrogen-evolving efficiency of the annulated cobalt(II) complex 1 that contains two labile axial ligands is more than three times as high as that of the encapsulated cobalt(III) complex 3 that has a single macrobicyclic ligand. The different pathways for formation of the cobalt(I) species from these two types of cobaloximes are discussed on the basis of the results obtained from fluorescence and laser flash photolysis spectroscopic studies.

Hydrogen Production by Noble-Metal-Free Molecular Catalysts and Related Nanomaterials

Co-reporter:Mei Wang ;Licheng Sun

ChemSusChem 2010 Volume 3( Issue 5) pp:551-554

Publication Date(Web):

DOI:10.1002/cssc.201000062

Preparation, Facile Deprotonation, and Rapid H/D Exchange of the μ-Hydride Diiron Model Complexes of the [FeFe]-Hydrogenase Containing a Pendant Amine in a Chelating Diphosphine Ligand

Co-reporter:Ning Wang, Mei Wang, Jihong Liu, Kun Jin, Lin Chen and Licheng Sun

Inorganic Chemistry 2009 Volume 48(Issue 24) pp:11551-11558

Publication Date(Web):November 24, 2009

DOI:10.1021/ic901154m

The CO-displacement of [(μ-pdt)Fe2(CO)6] with (Ph2PCH2)2N(n-Pr) in refluxing toluene gave an unsymmetrical chelating complex [(μ-pdt){Fe(CO)3}{Fe(CO)(κ2-Ph2PCH2N(n-Pr)CH2PPh2}] (1) as a major product, together with a small amount of the symmetrical intramolecular bridging complex [(μ-pdt){μ-Ph2PCH2N(n-Pr)CH2PPh2}{Fe(CO)2}2] (2) and the intermolecular bridging complex [{μ,κ1,κ1-Ph2PCH2N(n-Pr)CH2PPh2}{(μ-pdt)Fe2(CO)5}2] (3). In contrast, the reaction of [(μ-pdt)Fe2(CO)6] with (Ph2PCH2)2NR (R = n-Pr, Ph) afforded the intermolecular bridging isomers 3 and 4 in the presence of a CO-removing reagent Me3NO·2H2O in CH3CN at room temperature. The molecular structures of 1, 3, and 4, as well as the doubly protonated complex [1(HNHμ)](OTf)2] were determined by X-ray analyses. The protonation processes of 1 with HBF4·Et2O and HOTf were studied in different solvents. The presence of the Hμ···HN interaction in [1(HNHμ)]2+ was studied by relaxation time T1 and spin saturation transfer measurements. The μ-hydride of [1(Hμ)]+ and [1(HNHμ)]2+ undergo facile deprotonation with aniline and rapid H/D exchange with deuterons in solution. In contrast, neither deprotonation nor H/D exchange was detected for [(μ-H)(μ-pdt){Fe(CO)3}{Fe(CO)(κ2-dppp)}]+ ([5(Hμ)]+, dppp = Ph2PCH2CH2CH2PPh2) without internal base.

Synthesis, protonation and electrochemical properties of trinuclear NiFe2 complexes Fe2(CO)6(μ3-S)2[Ni(Ph2PCH2)2NR] (R = n-Bu, Ph) with an internal pendant nitrogen base as a proton relay

Co-reporter:Lele Duan, Mei Wang, Ping Li, Ning Wang, Fujun Wang, Licheng Sun

Inorganica Chimica Acta 2009 Volume 362(Issue 2) pp:372-376

Publication Date(Web):20 January 2009

DOI:10.1016/j.ica.2008.04.011

Two trinuclear NiFe2 complexes Fe2(CO)6(μ3-S)2[Ni(Ph2PCH2)2NR] (R = n-Bu, 1; Ph, 2) containing an internal base were prepared as biomimetic models for the active sites of FeFe and NiFe hydrogenases. Treatment of complex Fe2(CO)6(μ3-S)2[Ni(Ph2PCH2)2N(n-Bu)] (1) with HOTf gave an N-protonated complex [Fe2(CO)6(μ3-S)2{Ni(Ph2PCH2)2NH(n-Bu)}][OTf] ([1H][OTf]). The structures of complexes 1, 2 and [1H][OTf] were determined by X-ray crystallography, which shows that the proton held by the N atom of [1H][OTf] lies in an equatorial position. Cyclic voltammograms of complexes 1 and [1H][OTf] were studied and compared with that of Fe2(CO)6(μ3-S)2[Ni(dppe)].Trinuclear NiFe2 complexes Fe2(CO)6(μ3-S)2[Ni(Ph2PCH2)2NR] (R = n-Bu, 1; Ph, 2) containing an internal base were prepared and structurally characterized as biomimetic models for the active sites of FeFe and NiFe hydrogenases. The N atom in 1 can readily catch a proton from HOTf to form [1H][OTf], which regenerates 1 quickly and quantitatively in the presence of aniline.

Protophilicity, electrochemical property, and desulfurization of diiron dithiolate complexes containing a functionalized C2 bridge with two vicinal basic sites

Co-reporter:Ting-Ting Zhang, Mei Wang, Ning Wang, Ping Li, Zheng-Yi Liu, Li-Cheng Sun

Polyhedron 2009 28(6) pp: 1138-1144

Publication Date(Web):

DOI:10.1016/j.poly.2009.01.006

Photochemical hydrogen production catalyzed by polypyridyl ruthenium–cobaloxime heterobinuclear complexes with different bridges

Co-reporter:Cheng Li, Mei Wang, Jingxi Pan, Pan Zhang, Rong Zhang, Licheng Sun

Journal of Organometallic Chemistry 2009 694(17) pp: 2814-2819

Publication Date(Web):

DOI:10.1016/j.jorganchem.2009.04.041

Synthesis and characterization of carboxy-functionalized diiron model complexes of [FeFe]-hydrogenases: Decarboxylation of Ph2PCH2COOH promoted by a diiron azadithiolate complex

Co-reporter:Zhenbo Zhao, Mei Wang, Weibing Dong, Ping Li, Ze Yu, Licheng Sun

Journal of Organometallic Chemistry 2009 694(15) pp: 2309-2314

Publication Date(Web):

DOI:10.1016/j.jorganchem.2009.03.039

A proton–hydride diiron complex with a base-containing diphosphine ligand relevant to the [FeFe]-hydrogenase active site

Co-reporter:Ning Wang, Mei Wang, Tingting Zhang, Ping Li, Jihong Liu and Licheng Sun

Chemical Communications 2008 (Issue 44) pp:5800-5802

Publication Date(Web):01 Oct 2008

DOI:10.1039/B811352A

A diiron dithiolate complex holding a μ-hydride on the iron atoms and a proton on the basic site of a chelating diphosphine ligand was prepared and crystallographically characterized as a structural model of the [FeFe]-hydrogenase active site, and its molecular structure shows the Hμ−⋯HN+ distance is 3.934 Å.

CO-Migration in the Ligand Substitution Process of the Chelating Diphosphite Diiron Complex (μ-pdt)[Fe(CO)3][Fe(CO){(EtO)2PN(Me)P(OEt)2}]

Co-reporter:Ning Wang ; Mei Wang ; Tianbiao Liu ; Ping Li ; Tingting Zhang ; Marcetta Y. Darensbourg ;Licheng Sun

Inorganic Chemistry 2008 Volume 47(Issue 15) pp:6948-6955

Publication Date(Web):July 9, 2008

DOI:10.1021/ic800525n

Selective synthetic routes to isomeric diiron dithiolate complexes containing the (EtO)2PN(Me)P(OEt)2 (PNP) ligand in an unsymmetrical chelating role, for example, (μ-pdt)[Fe(CO)3][Fe(CO)(κ2-PNP)] (3) and as a symmetrically bridging ligand in (μ-pdt)(μ-PNP)[Fe(CO)2]2 (4), have been developed. 3 was converted to 4 in 75% yield after extensive reflux in toluene. The reactions of 3 with PMe3 and P(OEt)3 afforded bis-monodentate P-donor complexes (μ-pdt)[Fe(CO)2PR3][Fe(CO)2(PNP)] (PR3 = PMe3, 5; P(OEt)3, 7), respectively, which are formed via an associative PMe3 coordination reaction followed by an intramolecular CO-migration process from the Fe(CO)3 to the Fe(CO)(PNP) unit with concomitant opening of the Fe−PNP chelate ring. The PNP−monodentate complexes 5 and 7 were converted to a trisubstituted diiron complex (μ-pdt)(μ-PNP)[Fe(CO)PR3][Fe(CO)2] (PR3 = PMe3, 6; P(OEt)3, 8) on release of 1 equiv CO when refluxing in toluene. Variable-temperature 31P NMR spectra show that trisubstituted diiron complexes each exist as two configuration isomers in solution. All diiron dithiolate complexes obtained were characterized by MS, IR, NMR spectroscopy, elemental analysis, and X-ray diffraction studies.

Visible Light-Driven Electron Transfer and Hydrogen Generation Catalyzed by Bioinspired [2Fe2S] Complexes

Co-reporter:Yong Na ; Mei Wang ; Jingxi Pan ; Pan Zhang ; Björn Åkermark ;Licheng Sun

Inorganic Chemistry 2008 Volume 47(Issue 7) pp:2805-2810

Publication Date(Web):March 12, 2008

DOI:10.1021/ic702010w

Complexes [{(μ-SCH2)2NCH2C6H5}{Fe(CO)2L1}{Fe(CO)2L2}] (L1 = CO, L2 = P(Pyr)3, 2; L1 = L2 = P(Pyr)3, 3) were prepared, which have the lowest reduction potentials for the mono- and double-CO-displaced diiron complexes reported so far. Hydrogen evolution, driven by visible light, was successfully observed for a three-component system, consisting of a ruthenium polypyridine complex, the biomimetic model complex 2 or 3, and ascorbic acid as both electron and proton donor in CH3CN/H2O. The electron transfer from photogenerated Ru(bpy)3+ to 2 or 3 was detected by laser flash photolysis. Under optimal conditions, the total turnover number for hydrogen evolution was 4.3 based on 2 and 86 based on Ru(bpy)32+ in a three-hour photolysis.

Diiron dithiolate complexes containing intra-ligand NH⋯S hydrogen bonds: [FeFe] hydrogenase active site models for the electrochemical proton reduction of HOAc with low overpotential

Co-reporter:Ze Yu, Mei Wang, Ping Li, Weibing Dong, Fujun Wang and Licheng Sun

Dalton Transactions 2008 (Issue 18) pp:2400-2406

Publication Date(Web):07 Mar 2008

DOI:10.1039/B715990K

Four diiron dithiolate complexes containing ortho-acylamino-functionalized arenethiolato ligands, [(μ-S-2-RCONHC6H4)2Fe2(CO)6] (R = CH3, 1; CF3, 2; C6H5, 3; 4-FC6H4, 4), were synthesized and well characterized as biomimetic models of the Fe–Fe hydrogenase active site. The molecular structures of 3 and 4 were determined by X-ray crystallography. The intra-ligand NH⋯S hydrogen bonds were studied by the X-ray analysis and by the 1H NMR spectroscopy. The contribution of the NH⋯S hydrogen bonds to the reduction potentials of complexes 1–4 was investigated by electrochemistry. The first reduction potentials of complexes 1–4 exhibit large positive shifts, that is, 220–320 mV in comparison to that of the analogous complex [(μ-SPh)2Fe2(CO)6] and 370–470 mV to that of [(μ-pdt)2Fe2(CO)6] (pdt = propane-1,3-dithiolato). Complex 4 is capable of electrocatalysing proton reduction of acetic acid at relatively low overpotential (ca. 0.2 V) in acetonitrile.

[FeFe]-Hydrogenase active site models with relatively low reduction potentials: Diiron dithiolate complexes containing rigid bridges

Co-reporter:Ping Li, Mei Wang, Jingxi Pan, Lin Chen, Ning Wang, Licheng Sun

Journal of Inorganic Biochemistry 2008 Volume 102(Issue 4) pp:952-959

Publication Date(Web):April 2008

DOI:10.1016/j.jinorgbio.2007.12.018

Three diiron dithiolate complexes containing rigid and conjugated bridges, [μ-SC6H4-2-(CO)S-μ]Fe2(CO)6 (1), [2-μ-SC5H3N-3-(CO)S-μ]Fe2(CO)6 (2), and the PPh3-monosubstituted complex [μ-SC6H4-2-(CO)S-μ]Fe2(CO)5(PPh3) (1-P), were prepared as biomimetic models for the [FeFe]-hydrogenase active site. The structures of complexes 1 and 2 were determined by single crystal X-ray analysis, which shows that each complex features a rigid coplanar dithiolate bridge with a 2–3° deviation from the bisect plane of the molecule. The influence of the rigid bridge on the reduction potentials of complexes 1, 2 and 1-P was investigated by electrochemistry. The cyclic voltammograms of complexes 1 and 2 display large positive shifts for the primary reduction potentials, that is, 380–480 mV in comparison to that of the pdt-bridged (pdt = propane-1,3-dithiolato) complex (μ-pdt)Fe2(CO)6 and 160–260 mV to that of the bdt-bridged (bdt = benzene-1,2-dithiolato) analogue (μ-bdt)Fe2(CO)6.

Influence of substituents in the salicylaldehyde-derived Schiff bases on vanadium-catalyzed asymmetric oxidation of sulfides

Co-reporter:Haibin Liu;Ying Wang;Ran Yin;Wei Tian;Licheng Sun

Applied Organometallic Chemistry 2008 Volume 22( Issue 5) pp:253-257

Publication Date(Web):

DOI:10.1002/aoc.1386

Abstract

A series of chiral Schiff bases (L¹–L⁵) with different substituents in the salicylidenyl unit were prepared from condensation of 3-aryl-5-tert-butylsalicylaldehyde derivatives and optically active amino alcohols. Bromination of 3-phenyl-5-tert-butylsalicylaldehyde gave an unexpected product 3-(4-bromophenyl)-5-bromosalicylaldehyde, from which the corresponding Schiff base ligands L⁶ and L⁷, derived from (S)-valinol and (S)-tert-leucinol, respectively, were prepared. Ligands L¹–L⁷ were applied to the vanadium-catalyzed asymmetric oxidation of aryl methyl sulfides. Under the optimal conditions, the oxidation of the thioanisole with H₂O₂ as oxidant in CH₂Cl₂ catalyzed by VO(acac)₂-L¹–L⁷ gives good yields (74–83%) with moderate enantioselectivity (58–77% ee). Ligand L⁷, containing a 4-bromophenyl group on the 3-position and a Br atom on the 5-position of the salicylidenyl moiety, displays an 80–90% ee for vanadium-catalyzed oxidation of methyl 4-bromophenyl sulfide and methyl 2-naphthyl sulfide. Copyright © 2008 John Wiley & Sons, Ltd.

Carbene–pyridine chelating 2Fe2S hydrogenase model complexes as highly active catalysts for the electrochemical reduction of protons from weak acid (HOAc)

Co-reporter:Lele Duan, Mei Wang, Ping Li, Yong Na, Ning Wang and Licheng Sun

Dalton Transactions 2007 (Issue 13) pp:1277-1283

Publication Date(Web):26 Jan 2007

DOI:10.1039/B616645H

Two asymmetrically disubstituted diiron complexes (µ-pdt)[Fe(CO)3][Fe(CO)(η2-L)] (L = 1-methyl-3-(2-pyridyl)imidazol-2-ylidene (NHCMePy), 2; 1,3-bis(2-picolyl)imidazol-2-ylidene (NHCdiPic), 4) and a mono-substituted diiron complex (µ-pdt)[Fe(CO)3][Fe(CO)2(NHCdiPic)] (3) were prepared as biomimetic models of the Fe-only hydrogenase active site. X-Ray studies show that the NHCMePy and NHCdiPic ligands in 2 and 4 each coordinate to the single iron atom as NHC–Py chelating ligands in two basal positions and the NHCdiPic ligand of complex 3 lies in an apical position as a monodentate ligand. The large ranges of the highest and the lowest ν(CO) frequencies of 2 and 4 reflect that the relatively uneven electron density on the two iron atoms of the 2Fe2S model complexes 2 and 4 is as that observed for mono-substituted diiron complexes of good donor ligands. The cyclic voltammograms and the electrochemical proton reduction by 2 and 3 were studied in the presence of HOAc to evaluate the effect of asymmetrical substitution of strong donor ligands on the redox properties of the iron atoms and on the electrocatalytic activity for proton reduction.

Protonation, electrochemical properties and molecular structures of halogen-functionalized diiron azadithiolate complexes related to the active site of iron-only hydrogenases

Co-reporter:Fujun Wang, Mei Wang, Xiaoyang Liu, Kun Jin, Weibing Dong and Licheng Sun

Dalton Transactions 2007 (Issue 34) pp:3812-3819

Publication Date(Web):10 Jul 2007

DOI:10.1039/B706178A

Diiron complexes [{(µ-SCH2)2NCH2C6H4X}{Fe(CO)2L}2] (L = CO, X = 2-Br, 1; 2-F, 2; 3-Br, 3; L = PMe3, X = 2-Br, 4) were prepared as biomimetic models of the iron-only hydrogenase active site. The N-protonated species [1(NH)]+ClO4−, [2(NH)]+ClO4− and the µ-hydride diiron complex [4(FeHFe)]+PF6− were obtained in the presence of proton acids and well characterized. The protonation process of 4 was studied by in-situ IR and NMR spectroscopy, which suggests the formation of the diprotonated species [4(NH)(FeHFe)]2+ in the presence of an excess of proton acid. The molecular structures of 1, [1(NH)]+ClO4−, 4 and [4(FeHFe)]+PF6− were determined by X-ray crystallography. The single-crystal X-ray analysis reveals that an intramolecular H⋯Br contact (2.82 Å) in the crystalline state of [1(NH)]+ClO4−. In the presence of 1–6 equiv of the stronger acid HOTf, complex 1 is readily protonated on the bridged-N atom and can electrochemically catalyze the proton reduction at a relatively mild potential (ca. −1.0 V). Complex 4 is also electrocatalytic active at −1.4 V in the presence of HOTf with formation of the µ-hydride diiron species.

Preparation, structures and electrochemical property of phosphine substituted diiron azadithiolates relevant to the active site of Fe-only hydrogenases

Co-reporter:Weibing Dong, Mei Wang, Tianbiao Liu, Xiaoyang Liu, Kun Jin, Licheng Sun

Journal of Inorganic Biochemistry 2007 Volume 101(Issue 3) pp:506-513

Publication Date(Web):March 2007

DOI:10.1016/j.jinorgbio.2006.11.013

Mono- and di-phosphine diiron azadithiolate complexes [{(μ-SCH2)2N(4-NO2C6H4)}Fe2(CO)5(PMe3)] (2), [{(μ-SCH2)2N(4-NO2C6H4)}{Fe(CO)2L}2] (3, L = PMe3; 4, PMe2Ph) and the μ-hydride diiron complex [3(FeHFe)]+[PF6]− were prepared as biomimetic models of the active site of Fe-only hydrogenases. The complexes 2–4 and [3(FeHFe)]+[PF6]− were characterized by IR, 31P, 1H and 13C NMR spectra and their molecular structures were determined by single crystal X-ray analyses. The PMe3 ligand in complex 2 lies on the basal position. The PMe3-disubstituted complex 3 exists as two configuration isomers, transoid basal/basal and apical/basal, in the crystalline state, while two PMe2Ph ligands of 4 are in an apical/basal orientation. The variable temperature 31P NMR spectra of 2 and 3 were made to have an insight into the existence of the possible conformation isomers of 2 and 3 in solution. The [3(FeHFe)]+ cation possesses the sole transoid ba/ba geometry as other reported μ-hydride diiron analogues. The electrocatalytic property of {(μ-SCH2)2NC6H5}[Fe(CO)2PMe3]2 (5) was studied for proton reduction in the presence of HOAc.

Phosphane and Phosphite Unsymmetrically Disubstituted Diiron Complexes Related to the Fe-Only Hydrogenase Active Site

Co-reporter:Ping Li;Chengjiang He;Xiaoyang Liu;Kun Jin;Licheng Sun

European Journal of Inorganic Chemistry 2007 Volume 2007(Issue 23) pp:

Publication Date(Web):18 JUN 2007

DOI:10.1002/ejic.200601184

A series of unsymmetrically disubstituted diiron complexes [(μ-pdt){Fe(CO)₂L¹}{Fe(CO)₂L²}] [pdt = 1,3-propanedithiolato; L¹ = PMe₃, L² = PMe₂Ph, 4; PPh₃, 5; PCy₃, 6; P(OEt)₃, 7; L¹ = PMe₂Ph, L² = PPh₃, 8; P(OEt)₃, 9; L¹ = P(OEt)₃, L² = PPh₃, 10; PCy₃, 11] and [(μ-edt){Fe(CO)₂PMe₃}{Fe(CO)₂PPh₃}] (edt = 1,2-ethanedithiolato, 12) were prepared by means of stepwise CO displacements of [(μ-pdt)Fe₂(CO)₆] and [(μ-edt)Fe₂(CO)₆] by different tertiary phosphane and phosphite ligands. The interconversion of the irondithiacyclohexane ring and the rotation of the [Fe(CO)₂PR₃] subunit were studied using by variable-temperature ³¹P{¹H} NMR spectroscopy of 4, 6 and 12 in solution. The molecular structures of 4–6, 8–10 and 12 show that complexes 4–6, 8, 9 and 12 possess an apical/basal coordination mode and complex 10 has an apical/apical conformation. The X-ray analyses indicate that the PMe₂Ph ligand in the apical position of the starting complex [(μ-pdt){Fe(CO)₃}{FeCO₂(PMe₂Ph)}] rotates to the basal position on conversion to the products 8 and 9. Cyclic voltammograms of 4–11 were studied both under argon and CO. The influences of the phosphane and phosphite ligands on the redox properties of the unsymmetrically disubstituted diiron complexes are discussed. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

Effect of Deprotonation of a Benzimidazolyl Ligand on the Redox Potential and the Structures of Mononuclear Ruthenium(II) Complexes

Co-reporter:Hongfei Sun;Kun Jin;Chengbing Ma;Rong Zhang;Licheng Sun

European Journal of Inorganic Chemistry 2007 Volume 2007(Issue 26) pp:

Publication Date(Web):7 AUG 2007

DOI:10.1002/ejic.200700549

A monoruthenium(II) complex of the benzimidazolyl ligand and its deprotonated counterpart were prepared and structurally characterized. The reversible protonation/deprotonation process of the ancillary ligand switches the redox potential of the ruthenium(II) core from 0.69 to 0.26 V vs. Ag/AgNO₃. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

An insight into the protonation property of a diiron azadithiolate complex pertinent to the active site of Fe-only hydrogenases

Co-reporter:Weibing Dong, Mei Wang, Xiaoyang Liu, Kun Jin, Guanghua Li, Fujun Wang and Licheng Sun

Chemical Communications 2006 (Issue 3) pp:305-307

Publication Date(Web):22 Nov 2005

DOI:10.1039/B513270C

Protonation of [{(μ-SCH2)2N(C6H4-p-NO2)}{Fe(CO)2(PMe3)}2] in the presence of 4 equiv. of HOTf afforded two species, a μ-hydride diiron complex, the molecular structure of which was crystallographically characterized, and a μ-S-protonated species, which was readily deprotonated in the presence of pyridine.

Mono- and binuclear complexes of iron(II) and iron(III) with an N4O ligand: synthesis, structures and catalytic properties in alkane oxidation

Co-reporter:Fei Li, Mei Wang, Chengbing Ma, Aiping Gao, Hongbo Chen and Licheng Sun

Dalton Transactions 2006 (Issue 20) pp:2427-2434

Publication Date(Web):15 Mar 2006

DOI:10.1039/B516697G

Three mononuclear iron complexes and one binuclear iron complex, [Fe(tpoen)Cl]·0.5(Fe2OCl6) (1), [Fe(tpoen)Cl]PF6 (2), Fe(tpoen)Cl3 (3) and [{Fe(tpoen)}2(µ-O)](ClO4)4 (4) (tpoen = N-(2-pyridylmethoxyethyl)-N,N-bis(2-pyridylmethyl)amine), were synthesized as functional models of non-heme iron oxygenases. Crystallographic studies revealed that the Fe(II) center of 1 is in a pseudooctahedral environment with a pentadentate N4O ligand and a chloride ion trans to the oxygen atom. The Fe(III) center of 3 is ligated by three nitrogen atoms of tpoen and three chloride ions in a facial configuration. Each Fe(III) center of 4 is coordinated with four nitrogen atoms and an oxygen atom of tpoen with the Fe–O–Fe angle of 172.0(3) Å. Complexes 2, 3 and 4 catalysed the oxidation of cyclohexane with H2O2 in the total TNs of 24–36 with A/K ratios of 1.9–2.4. Under the same conditions they also catalysed both the oxidation of ethylbenzene to benzylic alcohol and acetobenzene with good activity (30–47 TN) and low selectivity (A/K 0.7), and the oxidation of adamantane with moderate activity (15–18 TN) and low regioselectivity (3°/2° 3.0–3.2). With mCPBA as oxidant the catalytic activities of 2, 3 and 4 increased 1.8 to 2.3-fold for the oxidation of cyclohexane and ethylbenzene and 6.3 to 7.5-fold for the oxidation of adamantane. Drastic enhancement of the regioselectivity was observed in the oxidation of adamantane (3°/2° 18.5–30.3).

Spectroscopic and crystallographic evidence for the N-protonated FeIFeI azadithiolate complex related to the active site of Fe-only hydrogenases

Co-reporter:Fujun Wang, Mei Wang, Xiaoyang Liu, Kun Jin, Weibing Dong, Guanghua Li, Björn Åkermark and Licheng Sun

Chemical Communications 2005 (Issue 25) pp:3221-3223

Publication Date(Web):18 May 2005

DOI:10.1039/B503371C

The complex [{(μ-SCH2)2N(CH2C6H4-2-Br)}Fe2(CO)6] and its N-protonated species, as structural models of the Fe-only hydrogenase active site, were identified spectroscopically and crystallographically, and their molecular structures show the 0.04–0.1 Å lengthening of the three N–C bonds and an intramolecular H⋯Br contact (2.82 Å) in the crystalline state of the N-protonated species.

Preparation and structures of 6- and 7-coordinate salen-type zirconium complexes and their catalytic properties for oligomerization of ethylene

Co-reporter:Hongjun Zhu, Mei Wang, Chengbing Ma, Bo Li, Changneng Chen, Licheng Sun

Journal of Organometallic Chemistry 2005 Volume 690(Issue 17) pp:3929-3936

Publication Date(Web):1 September 2005

DOI:10.1016/j.jorganchem.2005.05.027

A series of salen-type zirconium complexes of the general formula LZrCl2 (L = N,N′-ethylenebis(salicylideneiminate), 3a; N,N′-ethylenebis(3,5-di-tert-butylsalicylideneiminate), 3b; N,N′-ethylenebis(5-methoxysalicylideneiminate), 3c; N,N′-ethylenebis(5-chlorosalicylideneiminate), 3d; N,N′-ethylenebis(5-nitrosalicylideneiminate), 3e; N,N′-o-phenylenebis(salicylideneiminate), 4a; N,N′-o-phenylenebis(3,5-di-tert-butylsalicylideneiminate), 4b; N,N′-o-phenylenebis(5-methoxysalicylideneiminate), 4c; N,N′-o-phenylenebis(5-chloro-salicylideneiminate), 4d) were prepared. The crystal structures of 6- and 7-coordinate zirconium complexes 4b and [4b · OCMe2] were determined by X-ray crystallography, which reveals that a salen-type zirconium complex possesses a labile coordination site on the Zr center with a relatively stable framework and that the coordination and the dissociation of O-donor molecules occur readily at this site. The catalytic properties of 3(a–e) and 4(a–d) were studied for ethylene oligomerization in combination with Et2AlCl as co-catalyst. Complex 3c featuring a methoxy-substituted salen ligand displayed higher activity than its analogous precursors having chloro and nitro groups as substituents. The catalytic reactions by 3(a–e) and 4(a–d) gave C4–C10 olefins and low-carbon linear α-olefins in good selectivity.Crystallographic studies reveal that the salen-type Zr complex features a labile coordination site on the Zr center. The association and dissociation of O-donor molecules occur readily on this site, which might be ligated by a monomer in ethylene oligomerization catalyzed by salen-type Zr complexes.

An Unusual Cyclization in a Bis(cysteinyl-S) Diiron Complex Related to the Active Site of Fe-Only Hydrogenases

Co-reporter:Chengjiang He ;Xiaofeng Zhang;Zhen Wang;Changneng Chen ;Jianhui Liu Dr.;Björn Åkermark ;Licheng Sun

Angewandte Chemie 2005 Volume 117(Issue 4) pp:

Publication Date(Web):11 JAN 2005

DOI:10.1002/ange.200590013

An Unusual Cyclization in a Bis(cysteinyl-S) Diiron Complex Related to the Active Site of Fe-Only Hydrogenases

Co-reporter:Chengjiang He ;Xiaofeng Zhang;Zhen Wang;Changneng Chen ;Jianhui Liu Dr.;Björn Åkermark ;Licheng Sun

Angewandte Chemie International Edition 2005 Volume 44(Issue 4) pp:

Publication Date(Web):11 JAN 2005

DOI:10.1002/anie.200590013

An Unusual Cyclization in a Bis(cysteinyl-S) Diiron Complex Related to the Active Site of Fe-Only Hydrogenases

Co-reporter:Chengjiang He ;Xiaofeng Zhang;Zhen Wang;Changneng Chen ;Jianhui Liu Dr.;Björn Åkermark ;Licheng Sun

Angewandte Chemie 2004 Volume 116(Issue 27) pp:

Publication Date(Web):29 JUN 2004

DOI:10.1002/ange.200453961

Klassische Organometallchemie wurde für die Synthese des zweikernigen Eisenkomplexes 1 mit zwei geschützten (Cysteinyl-S)-Liganden genutzt. Die oxidative Addition des Thiols an [Fe₃(CO)₁₂] lieferte den Komplex 1, der eine ungewöhnliche intramolekulare nucleophile Cyclisierung unter Inversion der Konfiguration eingeht, bei der der chirale kohlenstoffüberbrückte Dieisenkomplex 2 entsteht.

An Unusual Cyclization in a Bis(cysteinyl-S) Diiron Complex Related to the Active Site of Fe-Only Hydrogenases

Co-reporter:Chengjiang He ;Xiaofeng Zhang;Zhen Wang;Changneng Chen ;Jianhui Liu Dr.;Björn Åkermark ;Licheng Sun

Angewandte Chemie International Edition 2004 Volume 43(Issue 27) pp:

Publication Date(Web):29 JUN 2004

DOI:10.1002/anie.200453961

Classical organometallic chemistry was used to prepare the dinuclear iron complex 1 with two protected cysteinyl-S ligands. Oxidative addition of the thiol to [Fe₃(CO)₁₂] gave complex 1, which undergoes an unusual intramolecular nucleophilic cyclization with inversion of the configuration to form the chiral carbon-bridged diiron complex 2.

Highly enantioselective sulfoxidation with vanadium catalysts of Schiff bases derived from bromo- and iodo-functionalized hydroxynaphthaldehydes

Co-reporter:Ying Wang, Mei Wang, Yu Wang, Xiuna Wang, Lin Wang, Licheng Sun

Journal of Catalysis (28 July 2010) Volume 273(Issue 2) pp:177-181

Publication Date(Web):28 July 2010

DOI:10.1016/j.jcat.2010.05.013

Two series of chiral Schiff bases, 4a−e and 5a−e, prepared from the condensation of the mono-, di-, tribromohydroxynaphthaldehyde or monoiodohydroxynaphthaldehyde with chiral amino alcohols, were used in combination with VO(acac)2 for the asymmetric oxidation of aryl methyl sulfides using H2O2 as terminal oxidant. Among these Schiff bases, dibromo-functionalized 4d and iodo-functionalized 5e gave high yields (91–93%) with good enantioselectivities (80–82% ee) for the oxidation of thioanisole in dichloromethane. The asymmetric oxidation of thioanisole in toluene using these Schiff bases gave methyl phenyl sulfoxide in satisfactory isolated yields (48–62%) with high enantioselectivities (91–94% ee), which were further improved by a modified procedure with the ee value up to 98% in 62% yield. The oxidations of other aryl methyl sulfides in toluene with dibromo- and iodo-functionalized Schiff bases 5d and 5e as ligands using the modified procedure afforded the corresponding sulfoxides in 55–67% isolated yields with 95–99% ee.Chiral Schiff bases with a bromo- and iodo-functionalized naphthyl backbone proved to be efficient ligands for the vanadium-catalyzed asymmetric oxidation of aryl methyl sulfides in dichloromethane and toluene with up to 99% ee and moderate-to-high isolated yields.Download high-res image (83KB)Download full-size image

The influence of a S-to-S bridge in diiron dithiolate models on the oxidation reaction: a mimic of the Hairox state of [FeFe]-hydrogenases

Co-reporter:Dehua Zheng, Mei Wang, Lin Chen, Ning Wang, Minglun Cheng and Licheng Sun

Chemical Communications 2014 - vol. 50(Issue 66) pp:NaN9258-9258

Publication Date(Web):2014/06/05

DOI:10.1039/C4CC03583F

Two-electron oxidation of a diiron complex (1) containing a bulky S-to-S bridge with an exocyclic carbonyl group affords [1(OH)]+, which replicates the coordination structure and electronic configuration of Hairox, and the chemically reversible reaction between 1 and [1(OH)]+ mimics the bioprocess of interconversion of the inactive Hairox and the active Hred states of the [FeFe]-hydrogenases.

Photochemical hydrogen production from water catalyzed by CdTe quantum dots/molecular cobalt catalyst hybrid systems

Co-reporter:Kai Han, Mei Wang, Shuai Zhang, Suli Wu, Yong Yang and Licheng Sun

Chemical Communications 2015 - vol. 51(Issue 32) pp:NaN7011-7011

Publication Date(Web):2015/03/17

DOI:10.1039/C5CC00536A

A hybrid system with a coordinative interaction between a cobalt complex of a N2S2-tetradentate ligand and CdTe quantum dots displayed a high activity (initial TOF 850 h−1) and improved stability (TON 1.44 × 104 based on catalyst over 30 h) for the photochemical H2 generation from water, with a quantum efficiency of 5.32% at 400 nm.

Highly efficient molecular nickel catalysts for electrochemical hydrogen production from neutral water

Co-reporter:Peili Zhang, Mei Wang, Yong Yang, Dehua Zheng, Kai Han and Licheng Sun

Chemical Communications 2014 - vol. 50(Issue 91) pp:NaN14156-14156

Publication Date(Web):2014/09/22

DOI:10.1039/C4CC05511J

A series of nickel complexes containing N5-pentadentate ligands with different amine-to-pyridine ratios were studied for electrochemical H2 production in neutral water and the one with a diamine–tripyridine ligand displays a TON of up to 308000 over 60 h electrolysis at −1.25 V vs. SHE, with a Faradaic efficiency of ∼91%.

Electrocatalytic hydrogen evolution from neutral water by molecular cobalt tripyridine–diamine complexes

Co-reporter:Peili Zhang, Mei Wang, Frederic Gloaguen, Lin Chen, François Quentel and Licheng Sun

Chemical Communications 2013 - vol. 49(Issue 82) pp:NaN9457-9457

Publication Date(Web):2013/07/08

DOI:10.1039/C3CC43491E

A cobalt complex with a tripyridine–diamine pentadentate ligand was found to be a highly active catalyst for electrochemical H2 production from neutral water, with an activity of 860 mol H2 (mol cat)−1 h−1 (cm2 Hg)−1 over 60 h CPE experiment at −1.25 V in a pH 7 phosphate buffer solution, without considerable deactivation.

A proton–hydride diiron complex with a base-containing diphosphine ligand relevant to the [FeFe]-hydrogenase active site

Co-reporter:Ning Wang, Mei Wang, Tingting Zhang, Ping Li, Jihong Liu and Licheng Sun

Chemical Communications 2008(Issue 44) pp:NaN5802-5802

Publication Date(Web):2008/10/01

DOI:10.1039/B811352A

A diiron dithiolate complex holding a μ-hydride on the iron atoms and a proton on the basic site of a chelating diphosphine ligand was prepared and crystallographically characterized as a structural model of the [FeFe]-hydrogenase active site, and its molecular structure shows the Hμ−⋯HN+ distance is 3.934 Å.

Photochemical H2 production with noble-metal-free molecular devices comprising a porphyrin photosensitizer and a cobaloxime catalyst

Co-reporter:Pan Zhang, Mei Wang, Caixia Li, Xueqiang Li, Jingfeng Dong and Licheng Sun

Chemical Communications 2010 - vol. 46(Issue 46) pp:NaN8808-8808

Publication Date(Web):2010/10/19

DOI:10.1039/C0CC03154B

Among three noble-metal-free molecular devices (1–3) containing a porphyrin photosensitizer and a cobaloxime catalyst, the one with a zinc porphyrin unit displayed apparently higher efficiency for photoinduced H2 production than complex 2 with a magnesium porphyrin and 3 with a free-base porphyrin, possibly due to the formation of a TEA⋯ZnPor–Co triad in solution.

Preparation and structures of enantiomeric dinuclear zirconium and hafnium complexes containing two homochiral N atoms, and their catalytic property for polymerization of rac-lactide

Co-reporter:Minggang Hu, Mei Wang, Hongjun Zhu, Lu Zhang, Hui Zhang and Licheng Sun

Dalton Transactions 2010 - vol. 39(Issue 18) pp:NaN4446-4446

Publication Date(Web):2010/03/31

DOI:10.1039/C001148G

The hydroxy- and phenoxy-bridged dinuclear zirconium and hafnium complexes 2 and 3 of an amine-pyridine-bis(phenolate) ligand (H2L) were prepared from the reaction of Na2L and ZrCl4 in the presence of 0.5 equiv of water in THF, while the reaction of H2L with NaH and then with ZrCl4 in the freshly distilled THF gave an eight-coordinate bis(homoleptic) mononuclear complex L2Zr (1). Two homochiral N atoms were created in each complex upon coordination of the unsymmetric tertiary amine ligands to the metal centers. Enantiomeric dinuclear complexes 2 and 3 both undergo spontaneous resolution during crystallization. The molecular structure of each enantiomer of 2 and 3, as well as the structure of 1, was determined by X-ray analysis and the circular dichroism spectra of N(R)N(R)-2 and N(S)N(S)-2 were studied. The racemates of 2 and 3 catalyzed controlled polymerization of rac-lactide in terms of the linearity of molecular weight versus conversion, forming isotactic-rich polylactide in high yields with a narrow polydispersity.

Homogeneous photocatalytic production of hydrogen from water by a bioinspired [Fe2S2] catalyst with high turnover numbers

Co-reporter:Pan Zhang, Mei Wang, Yong Na, Xueqiang Li, Yi Jiang and Licheng Sun

Dalton Transactions 2010 - vol. 39(Issue 5) pp:NaN1206-1206

Publication Date(Web):2009/11/24

DOI:10.1039/B923159P

A three-component homogeneous catalyst system, composed of a cyclometalated iridium(III) photosensitizer, a bioinspired diiron complex, and TEA in aqueous acetone, proved to be catalytically active for photoinduced H2 production, with up to 660 turnovers over 8 h of irradiation.

Diiron dithiolate complexes containing intra-ligand NH⋯S hydrogen bonds: [FeFe] hydrogenase active site models for the electrochemical proton reduction of HOAc with low overpotential

Co-reporter:Ze Yu, Mei Wang, Ping Li, Weibing Dong, Fujun Wang and Licheng Sun

Dalton Transactions 2008(Issue 18) pp:NaN2406-2406

Publication Date(Web):2008/03/07

DOI:10.1039/B715990K

Four diiron dithiolate complexes containing ortho-acylamino-functionalized arenethiolato ligands, [(μ-S-2-RCONHC6H4)2Fe2(CO)6] (R = CH3, 1; CF3, 2; C6H5, 3; 4-FC6H4, 4), were synthesized and well characterized as biomimetic models of the Fe–Fe hydrogenase active site. The molecular structures of 3 and 4 were determined by X-ray crystallography. The intra-ligand NH⋯S hydrogen bonds were studied by the X-ray analysis and by the 1H NMR spectroscopy. The contribution of the NH⋯S hydrogen bonds to the reduction potentials of complexes 1–4 was investigated by electrochemistry. The first reduction potentials of complexes 1–4 exhibit large positive shifts, that is, 220–320 mV in comparison to that of the analogous complex [(μ-SPh)2Fe2(CO)6] and 370–470 mV to that of [(μ-pdt)2Fe2(CO)6] (pdt = propane-1,3-dithiolato). Complex 4 is capable of electrocatalysing proton reduction of acetic acid at relatively low overpotential (ca. 0.2 V) in acetonitrile.

Carbene–pyridine chelating 2Fe2S hydrogenase model complexes as highly active catalysts for the electrochemical reduction of protons from weak acid (HOAc)

Co-reporter:Lele Duan, Mei Wang, Ping Li, Yong Na, Ning Wang and Licheng Sun

Dalton Transactions 2007(Issue 13) pp:NaN1283-1283

Publication Date(Web):2007/01/26

DOI:10.1039/B616645H

Two asymmetrically disubstituted diiron complexes (µ-pdt)[Fe(CO)3][Fe(CO)(η2-L)] (L = 1-methyl-3-(2-pyridyl)imidazol-2-ylidene (NHCMePy), 2; 1,3-bis(2-picolyl)imidazol-2-ylidene (NHCdiPic), 4) and a mono-substituted diiron complex (µ-pdt)[Fe(CO)3][Fe(CO)2(NHCdiPic)] (3) were prepared as biomimetic models of the Fe-only hydrogenase active site. X-Ray studies show that the NHCMePy and NHCdiPic ligands in 2 and 4 each coordinate to the single iron atom as NHC–Py chelating ligands in two basal positions and the NHCdiPic ligand of complex 3 lies in an apical position as a monodentate ligand. The large ranges of the highest and the lowest ν(CO) frequencies of 2 and 4 reflect that the relatively uneven electron density on the two iron atoms of the 2Fe2S model complexes 2 and 4 is as that observed for mono-substituted diiron complexes of good donor ligands. The cyclic voltammograms and the electrochemical proton reduction by 2 and 3 were studied in the presence of HOAc to evaluate the effect of asymmetrical substitution of strong donor ligands on the redox properties of the iron atoms and on the electrocatalytic activity for proton reduction.

Protonation, electrochemical properties and molecular structures of halogen-functionalized diiron azadithiolate complexes related to the active site of iron-only hydrogenases

Co-reporter:Fujun Wang, Mei Wang, Xiaoyang Liu, Kun Jin, Weibing Dong and Licheng Sun

Dalton Transactions 2007(Issue 34) pp:

Publication Date(Web):

DOI:10.1039/B706178A

CdSe quantum dots/molecular cobalt catalyst co-grafted open porous NiO film as a photocathode for visible light driven H2 evolution from neutral water

Co-reporter:Peng Meng, Mei Wang, Yong Yang, Shuai Zhang and Licheng Sun

Journal of Materials Chemistry A 2015 - vol. 3(Issue 37) pp:NaN18859-18859

Publication Date(Web):2015/08/20

DOI:10.1039/C5TA06255A

An active noble-metal-free photocathode was fabricated by co-grafting water-soluble thioglycolic acid-stabilized CdSe quantum dots and a molecular cobaloxime catalyst (CoP) through chemical linkage on a p-type open porous NiO film. This photocathode was used as a working electrode in a three-electrode cell, which displayed a photocurrent density up to 110 µA cm−2 at an applied potential of 0 V vs. NHE in 0.1 M Na2SO4 solution at pH 6.8 upon visible light illumination. The comparative studies showed that the open porous NiO/CdSe electrode did display a higher photocurrent density than that exhibited by an analogous planar NiO/CdSe electrode made by doctor-blading a NiO paste. Long-time photoelectrolysis experiments revealed that about 83% of the photocurrent density remained after 3.5 h illumination at −0.2 V vs. NHE. The open porous NiO/CdSe/CoP photocathode showed a considerably better current density and photocatalytic stability compared to the so-far reported dye- or QD-sensitized NiO cathodes with a cobaloxime catalyst chemically attached or physically adsorbed on the electrode surface under similar conditions.

Electrocatalytic water oxidation by copper(II) complexes containing a tetra- or pentadentate amine-pyridine ligand

Co-reporter:Junyu Shen, Mei Wang, Peili Zhang, Jian Jiang and Licheng Sun

Chemical Communications 2017 - vol. 53(Issue 31) pp:NaN4377-4377

Publication Date(Web):2017/03/24

DOI:10.1039/C7CC00332C

Two water soluble copper(II) complexes containing amine-pyridine ligands were found to be catalytically active for water oxidation reactions in basic solutions, with observed rate constants of 13.1–18.7 s−1. These complexes are robust in basic solutions and displayed good stability over 5 h of electrolysis in pH 11.5 phosphate buffer at 1.4 V vs. NHE.

Effect of the S-to-S bridge on the redox properties and H2 activation performance of diiron complexes related to the [FeFe]-hydrogenase active site

Co-reporter:Minglun Cheng, Mei Wang, Dehua Zheng and Licheng Sun

Dalton Transactions 2016 - vol. 45(Issue 44) pp:NaN17696-17696

Publication Date(Web):2016/10/04

DOI:10.1039/C6DT02953A

Three biomimetic models of the [FeFe]-hydrogenase active site, namely diiron dithiolates of [(μ-edt){Fe(CO)3}{Fe(CO)(κ2-PNP)}] (1, edt = ethane-1,2-dithiolate, PNP = Ph2PCH2N(nPr)CH2PPh2), [(μ-bdtMe){Fe(CO)3}{Fe(CO)(κ2-PNP)}] (2, bdtMe = 4-methylbenzene-1,2-dithiolate), and [(μ-adtBn){Fe(CO)3}{Fe(CO)(κ2-PNP)}] (3, adtBn = N-benzyl-2-azapropane-1,3-dithiolate), were prepared and structurally characterized. These complexes feature the same PNP ligand but different S-to-S bridges. Influence of the S-to-S bridge on the electrochemical properties and chemical oxidation reactivity of 1–3 was studied by cyclic voltammetry and by in situ IR spectroscopy. The results reveal that the S-to-S bridge has a considerable effect on the oxidation reactivity of 1–3 and on the stability of in situ generated single-electron oxidized complexes, [1]+, [2]+, and [3]+. The performances of [1]+ and [2]+ for H2 activation were explored in the presence of a mild chemical oxidant, while rapid decomposition of [3]+ thwarted the further study of this complex. Gratifyingly, 1 was found to be catalytically active, although in a low turnover number, for H2 oxidation in the presence of excess mild oxidant and a proton trapper under 1 atm H2 at room temperature.

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