Synthesis, Characterization, and Photocatalytic H2-Evolving Activity of a Family of [Co(N4Py)(X)](n+) Complexes in Aqueous Solution.

A series of [Co(III)(N4Py)(X)](ClO4)n (X = Cl(-), Br(-), OH(-), N3(-), NCS(-)-κN, n = 2: X = OH2, NCMe, DMSO-κO, n = 3) complexes containing the tetrapyridyl N5 ligand N4Py (N4Py = 1,1-di(pyridin-2-yl)-N,N-bis(pyridin-2-ylmethyl)methanamine) has been prepared and fully characterized by infrared (IR), UV-visible, and NMR spectroscopies, high-resolution electrospray ionization mass spectrometry (HRESI-MS), elemental analysis, X-ray crystallography, and electrochemistry. The reduced Co(II) and Co(I) species of these complexes have been also generated by bulk electrolyses in MeCN and characterized by UV-visible and EPR spectroscopies. All tested complexes are catalysts for the photocatalytic production of H2 from water at pH 4.0 in the presence of ascorbic acid/ascorbate, using [Ru(bpy)3](2+) as a photosensitizer, and all display similar H2-evolving activities. Detailed mechanistic studies show that while the complexes retain the monodentate X ligand upon electrochemical reduction to Co(II) species in MeCN solution, in aqueous solution, upon reduction by ascorbate (photocatalytic conditions), [Co(II)(N4Py)(HA)](+) is formed in all cases and is the precursor to the Co(I) species which presumably reacts with a proton. These results are in accordance with the fact that the H2-evolving activity does not depend on the chemical nature of the monodentate ligand and differ from those previously reported for similar complexes. The catalytic activity of this series of complexes in terms of turnover number versus catalyst (TONCat) was also found to be dependent on the catalyst concentration, with the highest value of 230 TONCat at 5 × 10(-6) M. As revealed by nanosecond transient absorption spectroscopy measurements, the first electron-transfer steps of the photocatalytic mechanism involve a reductive quenching of the excited state of [Ru(bpy)3](2+) by ascorbate followed by an electron transfer from [Ru(II)(bpy)2(bpy(•-))](+) to the [Co(II)(N4Py)(HA)](+) catalyst. The reduced catalyst then enters into the H2-evolution cycle.

[1]  F. Odobel,et al.  Photo-induced redox catalysis for proton reduction to hydrogen with homogeneous molecular systems using rhodium-based catalysts , 2015 .

[2]  M. Sliwa,et al.  Cobalt(III) tetraaza-macrocyclic complexes as efficient catalyst for photoinduced hydrogen production in water: Theoretical investigation of the electronic structure of the reduced species and mechanistic insight. , 2015, Journal of photochemistry and photobiology. B, Biology.

[3]  S. Ott,et al.  Water oxidation catalysed by a mononuclear Co(II) polypyridine complex; possible reaction intermediates and the role of the chloride ligand. , 2015, Chemical communications.

[4]  V. Artero,et al.  Recent Developments in Hydrogen Evolving Molecular Cobalt(II)-Polypyridyl Catalysts , 2015, Coordination chemistry reviews.

[5]  E. Fujita,et al.  Mechanistic studies of hydrogen evolution in aqueous solution catalyzed by a tertpyridine-amine cobalt complex. , 2015, Inorganic chemistry.

[6]  A. Deronzier,et al.  A computational mechanistic investigation of hydrogen production in water using the [Rh(III)(dmbpy)2Cl2](+)/[Ru(II)(bpy)3](2+)/ascorbic acid photocatalytic system. , 2015, Physical chemistry chemical physics : PCCP.

[7]  P. Rannou,et al.  Visible Light-Driven Electron Transfer from a Dye-Sensitized p-Type NiO Photocathode to a Molecular Catalyst in Solution: Toward NiO-Based Photoelectrochemical Devices for Solar Hydrogen Production , 2015 .

[8]  H. Wen,et al.  Hydrogen photogeneration catalyzed by a cobalt complex of a pentadentate aminopyridine-based ligand , 2015 .

[9]  C. J. McAdam,et al.  The pentadentate ligands 2PyN2Q and N4Py, and their Cu(II) and Zn(II) complexes: A synthetic, spectroscopic and crystallographic structural study , 2015 .

[10]  P. Hamm,et al.  Mechanism of photocatalytic hydrogen generation by a polypyridyl-based cobalt catalyst in aqueous solution. , 2015, Inorganic chemistry.

[11]  M. Kärkäs,et al.  Artificial photosynthesis: molecular systems for catalytic water oxidation. , 2014, Chemical reviews.

[12]  Licheng Sun,et al.  Highly efficient molecular nickel catalysts for electrochemical hydrogen production from neutral water. , 2014, Chemical communications.

[13]  Serena Berardi,et al.  Molecular artificial photosynthesis. , 2014, Chemical Society reviews.

[14]  M. Natali,et al.  Photoinduced hydrogen evolution by a pentapyridine cobalt complex: elucidating some mechanistic aspects. , 2014, Dalton transactions.

[15]  C. E. Webster,et al.  Electronic effects on a mononuclear Co complex with a pentadentate ligand for catalytic H₂ evolution. , 2014, Inorganic chemistry.

[16]  Miguel Guttentag,et al.  Ascorbate as an electron relay between an irreversible electron donor and Ru(II) or Re(I) photosensitizers. , 2014, Chemical communications.

[17]  Xuesong Wang,et al.  An unexpected role of the monodentate ligand in photocatalytic hydrogen production of the pentadentate ligand-based cobalt complexes. , 2014, Chemical communications.

[18]  Charles C. L. McCrory,et al.  Studies of Cobalt-Mediated Electrocatalytic CO2 Reduction Using a Redox-Active Ligand , 2014, Inorganic chemistry.

[19]  Christopher J. Chang,et al.  Towards a comprehensive understanding of visible-light photogeneration of hydrogen from water using cobalt(ii) polypyridyl catalysts , 2014 .

[20]  A. Llobet,et al.  Molecular water oxidation mechanisms followed by transition metals: state of the art. , 2014, Accounts of chemical research.

[21]  M. Sliwa,et al.  An efficient Ru(II) -Rh(III) -Ru(II) polypyridyl photocatalyst for visible-light-driven hydrogen production in aqueous solution. , 2014, Angewandte Chemie.

[22]  M. Natali,et al.  Efficient photocatalytic hydrogen generation from water by a cationic cobalt(II) porphyrin. , 2014, Chemical communications.

[23]  M. Field,et al.  A computational study of the mechanism of hydrogen evolution by cobalt(diimine-dioxime) catalysts. , 2013, Chemistry.

[24]  F. Molton,et al.  Efficient photocatalytic hydrogen production in water using a cobalt(III) tetraaza-macrocyclic catalyst: electrochemical generation of the low-valent Co(I) species and its reactivity toward proton reduction. , 2013, Physical chemistry chemical physics : PCCP.

[25]  Licheng Sun,et al.  Electrocatalytic hydrogen evolution from neutral water by molecular cobalt tripyridine-diamine complexes. , 2013, Chemical communications.

[26]  Travis A. White,et al.  Voltammetric and spectroscopic characterization of early intermediates in the Co(II)-polypyridyl-catalyzed reduction of water. , 2013, Chemical communications.

[27]  Rony S. Khnayzer,et al.  Catalytic proton reduction with transition metal complexes of the redox-active ligand bpy2PYMe , 2013 .

[28]  Timothy A. Jackson,et al.  Reaction landscape of a pentadentate N5-ligated Mn(II) complex with O2˙- and H2O2 includes conversion of a peroxomanganese(III) adduct to a bis(μ-oxo)dimanganese(III,IV) species. , 2013, Dalton transactions.

[29]  Pingwu Du,et al.  Cobalt complexes as artificial hydrogenases for the reductive side of water splitting. , 2013, Biochimica et biophysica acta.

[30]  S. Fukuzumi,et al.  Enhanced electron-transfer reactivity of nonheme manganese(IV)-oxo complexes by binding scandium ions. , 2013, Journal of the American Chemical Society.

[31]  Karin J. Young,et al.  An anionic N-donor ligand promotes manganese-catalyzed water oxidation. , 2013, Inorganic chemistry.

[32]  Brian H Solis,et al.  Effects of ligand modification and protonation on metal oxime hydrogen evolution electrocatalysts. , 2013, Inorganic chemistry.

[33]  Timothy A. Jackson,et al.  Spectroscopic properties and reactivity of a mononuclear oxomanganese(IV) complex. , 2013, Chemical communications.

[34]  Miguel Guttentag,et al.  3d element complexes of pentadentate bipyridine-pyridine-based ligand scaffolds: structures and photocatalytic activities. , 2013, Inorganic chemistry.

[35]  R. Schmehl,et al.  Mechanistic details for cobalt catalyzed photochemical hydrogen production in aqueous solution: efficiencies of the photochemical and non-photochemical steps. , 2013, Inorganic chemistry.

[36]  J. Long,et al.  A mechanistic study of proton reduction catalyzed by a pentapyridine cobalt complex: evidence for involvement of an anation-based pathway , 2013 .

[37]  J. Long,et al.  Complexes of earth-abundant metals for catalytic electrochemical hydrogen generation under aqueous conditions. , 2013, Chemical Society reviews.

[38]  S. Fukuzumi,et al.  A mononuclear non-heme manganese(IV)-oxo complex binding redox-inactive metal ions. , 2013, Journal of the American Chemical Society.

[39]  P. Hamm,et al.  A highly stable polypyridyl-based cobalt catalyst for homo- and heterogeneous photocatalytic water reduction. , 2013, Dalton transactions.

[40]  M. Sliwa,et al.  [Rh(III)(dmbpy)2Cl2]+ as a highly efficient catalyst for visible-light-driven hydrogen production in pure water: comparison with other rhodium catalysts. , 2013, Chemistry.

[41]  S. Shaik,et al.  Evidence for an alternative to the oxygen rebound mechanism in C-H bond activation by non-heme Fe(IV)O complexes. , 2012, Journal of the American Chemical Society.

[42]  S. Fukuzumi,et al.  Mechanistic insight into catalytic oxidations of organic compounds by ruthenium(IV)-oxo complexes with pyridylamine ligands , 2012 .

[43]  R. Eisenberg,et al.  Molecular systems for light driven hydrogen production. , 2012, Dalton transactions.

[44]  Yan Jiang,et al.  DFT studies of cobalt hydride intermediate on cobaloxime‐catalyzed H2 evolution pathways , 2012 .

[45]  C. Ko,et al.  A cobalt(II) quaterpyridine complex as a visible light-driven catalyst for both water oxidation and reduction , 2012 .

[46]  M. Field,et al.  Combined experimental-theoretical characterization of the hydrido-cobaloxime [HCo(dmgH)2(PnBu3)]. , 2012, Inorganic chemistry.

[47]  Nathan J. DeYonker,et al.  Electrocatalytic and photocatalytic hydrogen production in aqueous solution by a molecular cobalt complex. , 2012, Angewandte Chemie.

[48]  Mei Wang,et al.  Recent progress in electrochemical hydrogen production with earth-abundant metal complexes as catalysts , 2012 .

[49]  Pingwu Du,et al.  Catalysts made of earth-abundant elements (Co, Ni, Fe) for water splitting: Recent progress and future challenges , 2012 .

[50]  R. Wright,et al.  Isolation, observation, and computational modeling of proposed intermediates in catalytic proton reductions with the hydrogenase mimic Fe2(CO)6S2C6H4. , 2012, Dalton transactions.

[51]  E. Fujita,et al.  Theoretical studies of the mechanism of catalytic hydrogen production by a cobaloxime. , 2011, Chemical communications.

[52]  Sharon Hammes-Schiffer,et al.  Substituent effects on cobalt diglyoxime catalysts for hydrogen evolution. , 2011, Journal of the American Chemical Society.

[53]  Sharon Hammes-Schiffer,et al.  Theoretical analysis of mechanistic pathways for hydrogen evolution catalyzed by cobaloximes. , 2011, Inorganic chemistry.

[54]  Timothy A. Jackson,et al.  Geometric and electronic structures of peroxomanganese(III) complexes supported by pentadentate amino-pyridine and -imidazole ligands. , 2011, Inorganic chemistry.

[55]  M. Fontecave,et al.  Splitting water with cobalt. , 2011, Angewandte Chemie.

[56]  Yang Tian,et al.  Selective and sensitive determination of hydroxyl radicals generated from living cells through an electrochemical impedance method. , 2011, Chemical communications.

[57]  M. Radoń,et al.  Spin ground state and magnetic properties of cobalt(II): relativistic DFT calculations guided by EPR measurements of bis(2,4-acetylacetonate)cobalt(II)-based complexes. , 2011, The journal of physical chemistry. A.

[58]  M. Ogawa,et al.  Platinum(II)-based hydrogen-evolving catalysts linked to multipendant viologen acceptors: experimental and DFT indications for bimolecular pathways. , 2011, Chemistry.

[59]  Takeshi Kobayashi,et al.  Photocatalytic production of hydrogen by disproportionation of one-electron-reduced rhodium and iridium-ruthenium complexes in water. , 2011, Angewandte Chemie.

[60]  Timothy R. Cook,et al.  Solar energy supply and storage for the legacy and nonlegacy worlds. , 2010, Chemical reviews.

[61]  Sven Rau,et al.  Catalytic hydrogen production at cobalt centres , 2010 .

[62]  A. Deronzier,et al.  Synthesis and properties of trinuclear polypyridyl complexes Ru(II)–Co(II)–Ru(II) and Ru(II)–Co(III)–Ru(II): Their photoinduced interconversion , 2010 .

[63]  Harry B Gray,et al.  Powering the planet with solar fuel. , 2009, Nature chemistry.

[64]  N. Lewis,et al.  Powering the planet: Chemical challenges in solar energy utilization , 2006, Proceedings of the National Academy of Sciences.

[65]  J. Manso,et al.  A kinetic approach to the alkylating potential of carcinogenic lactones. , 2005, Chemical research in toxicology.

[66]  Mi Hee Lim,et al.  Structural insights into nonheme alkylperoxoiron(III) and oxoiron(IV) intermediates by X-ray absorption spectroscopy. , 2004, Journal of the American Chemical Society.

[67]  J. Pinson,et al.  Electrochemical oxidation of aliphatic amines and their attachment to carbon and metal surfaces. , 2004, Langmuir : the ACS journal of surfaces and colloids.

[68]  A. Willis,et al.  A unique mechanism for base catalyzed hydrolysis of pentaaminecobalt(III) complexes containing picolyl residues. , 2003, Inorganic chemistry.

[69]  Hongyu Chen,et al.  Electrochemical properties of [MnIII(terpy)(N3)3] (terpy=2,2′:6′,2″-terpyridine) in CH3CN: Electrogeneration of dimanganese(II) di-μ-azido and dimanganese(IV) di-μ-oxo complexes , 2001 .

[70]  Louis J. Farrugia,et al.  WinGX suite for small-molecule single-crystal crystallography , 1999 .

[71]  A. Spek,et al.  Iron Chemistry of a Pentadentate Ligand That Generates a Metastable Fe(III)-OOH Intermediate. , 1999, Inorganic chemistry.

[72]  Maria Cristina Burla,et al.  SIR97: a new tool for crystal structure determination and refinement , 1999 .

[73]  R. Compton,et al.  Mechanistic Determination Using Arrays of Variable-Sized Channel Microband Electrodes: The Oxidation of Ascorbic Acid in Aqueous Solution , 1998 .

[74]  Louis J. Farrugia,et al.  ORTEP-3 for Windows - a version of ORTEP-III with a Graphical User Interface (GUI) , 1997 .

[75]  E. C. Wilkinson,et al.  NONHEME IRON CENTERS IN OXYGEN ACTIVATION : CHARACTERIZATION OF AN IRON(III) HYDROPEROXIDE INTERMEDIATE , 1995 .

[76]  X. You,et al.  Synthesis and X-ray crystal structure of a mixed-valent cobalt complex, Co2Cl5(py)5 , 1993 .

[77]  G. Tollin,et al.  Ionic strength dependence of the kinetics of electron transfer from bovine mitochondrial cytochrome c to bovine cytochrome c oxidase. , 1991, Biochemistry.

[78]  F. Keene,et al.  Reactivity of coordinated nitriles , 1981 .

[79]  D. Buckingham,et al.  Labile (sulfonato)pentaamminecobalt(III) complexes: synthesis and kinetics and mechanism of acid and base hydrolysis , 1981 .

[80]  B. Brunschwig,et al.  Homogeneous catalysis of the photoreduction of water by visible light. Mediation by a tris(2,2'-bipyridine)ruthenium(II)-cobalt(II) macrocycle system , 1979 .

[81]  R. Ziolo,et al.  Chemistry of coordinated azides , 1973 .

[82]  D. Buckingham,et al.  Mechanism of base hydrolysis for CoIII(NH3)5X2+ ions. Hydrolysis and rearrangement for the sulfur-bonded Co(NH3)5SCN2+ ion , 1970 .

[83]  H. Gray,et al.  Molecular and electronic structure of pentacyanocobaltate , 1967 .

[84]  J. Loveland,et al.  Anodic Voltammetry to +2.0 Volts. Application to Hydrocarbons and Oxidation Stability Studies , 1961 .

[85]  J. Long,et al.  Photocatalytic generation of hydrogen from water using a cobalt pentapyridine complex in combination with molecular and semiconductor nanowire photosensitizers , 2013 .

[86]  P. Hamm,et al.  Photocatalytic H2 Production with a Rhenium/Cobalt System in Water under Acidic Conditions , 2012 .

[87]  G. Sheldrick.  A short history of SHELX. , 2008, Acta crystallographica. Section A, Foundations of crystallography.

[88]  J. Leprêtre,et al.  Electrochemical properties of [FeIII(L)2Cl2][PF6] and [Fe2III,IIIO(L)4Cl2][PF6]2 [L=2,2′-bipyridine (bpy) and 4,4′-dimethyl-2,2′-bipyridine (dmbpy)]. Crystal structures of the dmbpy derivatives , 1999 .

[89]  R. L. Martin,et al.  Synthesis, structure and properties of cobalt(III) complexes of pentadentate ligands with pyridyl pendant arms , 1995 .

[90]  D. Cole-Hamilton,et al.  Photochemical hydrogen production from ascorbic acid catalysed by tris(2, 2′-bipyridyl)ruthenium(II) and hydridotris(triethylphosphine)palladium(II) , 1984 .

[91]  W. R. Bottoms,et al.  Photocatalytic generation of hydrogen from water , 1976 .

[92]  L. Beyer,et al.  Synthesis, characterization, and some reactions of (dimethyl sulfoxide)pentaammine cobalt(III) salts , 1973 .

[93]  J. Lunsford,et al.  Electron spin resonance spectra of five- and six-co-ordinate cobalt(II)–methyl isocyanide complexes in CoIIY zeolites , 1972 .