Nouveaux catalyseurs inspirés du site actif des hydrogénases NiFe : électro-production d'hydrogène et mécanisme catalytique

NiFe hydrogenases are unique metalloenzymes that catalyze H+/H2 interconversion with remarkable efficiency close to the thermodynamic potential. Their active site consists of a heterobimetallic complex containing a nickel ion in a sulphur-rich environment connected by two thiolates bridges to an organometallic cyano-carbonyl iron moiety. In order to improve the understanding of the enzymatic mechanism and to obtain new base-metal electrocatalysts for H2 production, we synthesized a series of bio-inspired low molecular weight model complexes with the butterfly structure Ni(µ-S2)M (M= Ru, Mn and Fe). All these compounds displayed a catalytic activity of hydrogen production. Modulating the electronic and steric properties of the ruthenium center allowed optimizing the catalytic performances of these compounds in terms of stability, catalytic rate and overpotential. Mechanistic studies of the catalytic cycle of the Ni-Ru complexes have also been carried out. They allowed us to suggest a bio-relevant bridging hydride as the catalytic intermediate. Finally, we synthesized one of the first Ni-Fe complexes that is both a structural and a functional model of NiFe hydrogenases.Les hydrogénases NiFe sont des métalloenzymes capables de catalyser efficacement la production et l'oxydation du dihydrogène à des potentiels proches de l'équilibre thermodynamique. Leur site actif est constitué d'un complexe hétérobimétallique comportant un atome de nickel en environnement soufré relié par deux ponts thiolates à un motif organométallique fer-cyano-carbonyle. Afin d'obtenir des catalyseurs de production d'hydrogène alternatifs au platine actuellement utilisé dans les électrolyseurs et pour approfondir la compréhension du mécanisme catalytique de l'enzyme, nous avons élaboré plusieurs modèles de faible poids moléculaire inspirés de la structure du site actif de ces enzymes : il s'agit de complexes dinucléaires possédant le motif papillon Ni(µ-S2)M (M= Ru, Mn et Fe). Les propriétés électrocatalytiques de ces composés ont été évaluées : ils s'avèrent tous actifs en production d'hydrogène. La modification de la densité électronique et de l'encombrement stérique au niveau du centre ruthénium des complexes Ni-Ru synthétisés a permis d'optimiser les performances de ces catalyseurs en termes de stabilité, de vitesse de catalyse et de surtension. Une étude mécanistique du cycle catalytique des complexes Ni-Ru a également été menée : en combinant mesures électrochimiques et calculs théoriques (DFT), elle a permis de proposer un intermédiaire catalytique hydrure de nature pontante entre les deux métaux Ni et Ru. Enfin, le complexe dinucléaire Ni-Fe synthétisé constitue l'un des premiers modèles à la fois structural et fonctionnel des hydrogénases NiFe

Nouveaux catalyseurs inspirés du site actif des hydrogénases NiFe : électro-production d'hydrogène et mécanisme catalytique

NiFe hydrogenases are unique metalloenzymes that catalyze H+/H2 interconversion with remarkable efficiency close to the thermodynamic potential. Their active site consists of a heterobimetallic complex containing a nickel ion in a sulphur-rich environment connected by two thiolates bridges to an organometallic cyano-carbonyl iron moiety. In order to improve the understanding of the enzymatic mechanism and to obtain new base-metal electrocatalysts for H2 production, we synthesized a series of bio-inspired low molecular weight model complexes with the butterfly structure Ni(µ-S2)M (M= Ru, Mn and Fe). All these compounds displayed a catalytic activity of hydrogen production. Modulating the electronic and steric properties of the ruthenium center allowed optimizing the catalytic performances of these compounds in terms of stability, catalytic rate and overpotential. Mechanistic studies of the catalytic cycle of the Ni-Ru complexes have also been carried out. They allowed us to suggest a bio-relevant bridging hydride as the catalytic intermediate. Finally, we synthesized one of the first Ni-Fe complexes that is both a structural and a functional model of NiFe hydrogenases.Les hydrogénases NiFe sont des métalloenzymes capables de catalyser efficacement la production et l'oxydation du dihydrogène à des potentiels proches de l'équilibre thermodynamique. Leur site actif est constitué d'un complexe hétérobimétallique comportant un atome de nickel en environnement soufré relié par deux ponts thiolates à un motif organométallique fer-cyano-carbonyle. Afin d'obtenir des catalyseurs de production d'hydrogène alternatifs au platine actuellement utilisé dans les électrolyseurs et pour approfondir la compréhension du mécanisme catalytique de l'enzyme, nous avons élaboré plusieurs modèles de faible poids moléculaire inspirés de la structure du site actif de ces enzymes : il s'agit de complexes dinucléaires possédant le motif papillon Ni(µ-S2)M (M= Ru, Mn et Fe). Les propriétés électrocatalytiques de ces composés ont été évaluées : ils s'avèrent tous actifs en production d'hydrogène. La modification de la densité électronique et de l'encombrement stérique au niveau du centre ruthénium des complexes Ni-Ru synthétisés a permis d'optimiser les performances de ces catalyseurs en termes de stabilité, de vitesse de catalyse et de surtension. Une étude mécanistique du cycle catalytique des complexes Ni-Ru a également été menée : en combinant mesures électrochimiques et calculs théoriques (DFT), elle a permis de proposer un intermédiaire catalytique hydrure de nature pontante entre les deux métaux Ni et Ru. Enfin, le complexe dinucléaire Ni-Fe synthétisé constitue l'un des premiers modèles à la fois structural et fonctionnel des hydrogénases NiFe

Modelling NiFe hydrogenases : Nickel-based electrocatalysts for hydrogen evolution

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Mechanism of hydrogen evolution catalyzed by NiFe hydrogenases: insights from a Ni-Ru model compound.

International audienceDFT modeling has been used to investigate a previously proposed mechanism of proton reduction catalyzed by [Ni(xbsms)Ru(CO)(2)Cl(2)] (H(2)xbsms = 1,2-bis(4-mercapto-3,3-dimethyl-2-thiabutyl)benzene), a bio-inspired mimic of NiFe hydrogenases based on a Ni-Ru framework. Protonation of the 2e(-)-reduced compound, from which a chloride anion has been eliminated, results in the formation of a semi-bridging hydride derivative with structural features comparable to those of the Ni-C state catalytic intermediate of native hydrogenases. The present study thus provides structural and functional insights into the enzymatic mechanism including the possible involvement of a bridging hydride derivative and heterolytic formation of a dihydrogen molecule on a {Ni(mu-S)(2)M} framework

A structural and functional mimic of the active site of NiFe hydrogenases.

International audienceThe structural mimic of the active site of NiFe hydrogenases, [Ni(xbsms)FeCp(CO)](BF(4)), is an electrocatalyst for hydrogen evolution from trifluoroacetic acid in DMF

Nickel-Manganese Catalysts as Biomimics of the active site of NiFe hydrogenases: a Combined Electrocatalytical and DFT Mechanistic Study

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A nickel–manganese catalyst as a biomimic of the active site of NiFe hydrogenases: a combined electrocatalytical and DFT mechanistic study

International audienceThe dinuclear nickel–manganese complex [Ni(xbsms)Mn(CO)3(H2O)]+ (H2xbsms = 1,2-bis(4-mercapto-3,3-dimethyl-2-thiabutyl)benzene) is reported as a bio-inspired mimic of the active site of NiFe hydrogenases catalyzing hydrogen evolution from trifluoroacetic acid in DMF with an overpotential requirement of 860 mV. This is higher than that displayed by Ni–Ru systems [Canaguier et al., Chem.–Eur. J., 2009, 15, 9350–9364] but similar to that found for related noble metal free Ni–Fe mimics [Canaguier et al., Chem. Commun. 2010, 46, 5876–5878]. A combined electrochemical and theoretical (DFT) study suggests a heterolytic mechanism for hydrogen evolution from a hydride derivative. The structure of the active intermediate, with a bridging hydride ligand between Ni and Mn, resembles that of the Ni–C active state of NiFe hydrogenases

Cyclopentadienyl Ruthenium–Nickel Catalysts for Biomimetic Hydrogen Evolution: Electrocatalytic Properties and Mechanistic DFT Studies

International audienceThe new dinuclear nickel–ruthenium complexes [Ni(xbsms)RuCp(L)][PF6] (H2xbsms=1,2-bis(4-mercapto-3,3-dimethyl-2-thiabutyl)benzene; Cp−=cyclopentadienyl; L=DMSO, CO, PPh3, and PCy3) are reported and are bioinspired mimics of NiFe hydrogenases. These compounds were characterized by X-ray diffraction techniques and display novel structural motifs. Interestingly, [Ni(xbsms)RuCpCO][PF6] is stereochemically nonrigid in solution and an isomerization mechanism was derived with the help of density functional theory (DFT) calculations. Because of an increased electron density on the metal centers [Eur. J. Inorg. Chem.2007, 18, 2613–2626] with respect to the previously described [Ni(xbsms)Ru(CO)2Cl2] and [Ni(xbsms)Ru(p-cymene)Cl]+ complexes, [Ni(xbsms)RuCp(dmso)][PF6] catalyzes hydrogen evolution from Et3NH+ in DMF with an overpotential reduced by 180 mV and thus represents the most efficient NiFe hydrogenase functional mimic. DFT calculations were carried out with several methods to investigate the catalytic cycle and, coupled with electrochemical measurements, allowed a mechanism to be proposed. A terminal or bridging hydride derivative was identified as the active intermediate, with the structure of the bridging form similar to that of the Ni[BOND]C active state of NiFe hydrogenases

Catalytic hydrogen production by a Ni-Ru mimic of NiFe hydrogenases involves a proton-coupled electron transfer step.

International audienceA combined electrochemical and theoretical study suggests that hydrogen evolution from weak acids catalyzed by a structural mimic of the active site of NiFe hydrogenases [Ni(xbsms)Ru(C6Me6)Cl](+) proceeds through proton-coupled electron transfer steps