Synthesis, structure and reactivity of Ni site models of [NiFeSe] hydrogenases

Abstract

A series of structural models of the Ni centre in [NiFeSe] hydrogenases has been developed which exhibits key structural features of the Ni site in the H2 cycling enzyme. Specifically, two complexes with a hydrogenase-analogous four-coordinate 'NiS3Se' primary coordination sphere and complexes with a 'NiS2Se2' and a 'NiS4' core are reported. The reactivity of the complexes towards oxygen and protons shows some relevance to the chemistry of [NiFeSe] hydrogenases. Exposure of a 'NiS3Se' complex to atmospheric oxygen results in the oxidation of the selenolate group in the complex to a diselenide, which is released from the nickel site. Oxidation of the selenolate ligand on Ni occurs approximately four times faster than oxidation with the analogous sulfur complex. Reaction of the complexes with one equivalent of HBF4 results in protonation of the monodentate chalcogenolate and the release of this ligand from the metal centre as a thiol or selenol. Unrelated to their biomimetic nature, the complexes serve also as molecular precursors to modify electrodes with Ni-S-Se containing particles by electrochemical deposition. The activated electrodes evolve H2 in pH neutral water with an electrocatalytic onset potential of -0.6 V and a current density of 15 μA cm(-2) at -0.75 V vs. NHE.

Synthetic Active Site Model of the [NiFeSe] Hydrogenase

“…The bond distances are as expected: the nickel selenolate distances of 2.295(8) Å in [Ni(‘S 2 Se 2 ’)] are longer than the nickel thiolate distances of 2.184(3) Å in [Ni(‘S 4 ’)],[ 17a ] as observed with other nickel thiolate/selenolate complexes. [ 18 ] The five-membered rings in [Ni(‘S 2 Se 2 ’)] constrain the Se-Ni-S angles negligibly to 89.3(4)° and the seven-membered ring of the xylenediyl group pushes the S1-Ni-S2 angle to 99.4(2)° . There is a small tetrahedral distortion from the square plane around the nickel center with an angle of 11.1±1° between the planes Se1-Ni-S1 and Se2-Ni-S2.…”

“…We have recently reported on a series of nickel complexes as structural models of the nickel center in the active sites of the [NiFeSe] hydrogenases. [ 18 ] Herein, we report a dinuclear [NiFeSe] hydrogenase active site model, which includes an iron carbonyl to replicate the core features of the enzyme active site. The synthesis, characterization, and activity of [NiFe(‘S 2 Se 2 ’)(CO) 3 ] is reported and it has been compared with the previously reported[ 15d ] thiolate analogue [NiFe(‘S 4 ’)(CO) 3 ] to determine the influence of the chalcogenate donor on the properties of the complex (Figure 1 ).…”

Proton‐Reduction Reaction Catalyzed by Homoleptic Nickel–bis‐1,2‐dithiolate Complexes: Experimental and Theoretical Mechanistic Investigations

“…Significant attention has been drawn to whether electrocatalysis in organic solvents is of homogeneous or heterogeneous nature. More specifically, several studies on similar dithiolene‐ or thiolate‐containing systems have shown that under reductive conditions a molecular catalyst may decompose to form a material which deposits on the surface of the electrode and is responsible for the catalytic performance . Several diagnostic criteria have been used to identify if a process is truly catalytic, most notably rinse tests in which the electrode, after a scan or a potential has been applied for a period of time, is transferred to a fresh solution containing only the acid.…”

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

“…However, low energy conversion wileyonlinelibrary.com overpotentials (−50 to −300 mV). [ 13,17,[31][32][33] In our previous studies, we found that the ionic copper complex, (Cu(bztpen)) 2+ (bztpen = N -benzyl-N , N′ , N′ -tris(2-pyridylmethyl)ethylenediamine), was a highly active molecular catalyst for the HER, [ 34 ] but it gradually deposited on the surface of glassy carbon electrode (GCE) during long-term bulk electrolysis at −0.90 V versus standard hydrogen electrode (SHE). With curiosity to know more about the material deposited from (Cu(bztpen)) 2+ , we made continuous detailed studies on this material.…”