Activation of H2 and CO by Sulfur‐Rich Nickel Model Complexes for [NiFe] Hydrogenases and CO Dehydrogenases

Publisher Website
Google Scholar
Abstract
Reactions of the trinuclear complexes [Ni(RS3)]3 [HS32− = bis(2‐mercaptophenyl)sulfide(2−) (1a) or siS32− = bis(2‐mercapto‐3‐trimethylsilylphenyl)sulfide(2−) (1b)] with nucleophiles L (L = NHPnPr3, NHPCy3, NHSPh2, PnPr3) afforded the corresponding mononuclear complexes [Ni(L)(RS3)] [R = si = SiMe3; L = NHPnPr3 (2b); L = NHPCy3 (3a,b); L = NHSPh2 (4a,b); L = PnPr3 (5a)]. X‐ray structural determinations showed that 2b, 3a, 3b, 4a, and 5a exhibit tetrahedrally distorted planar [Ni(L)(RS3)] fragments. Complex 2b dimerizes through intermolecular N−H···N hydrogen bonding. In contrast to 2b, complexes 3a and 4a exhibit intramolecular hydrogen bonds between thiol groups and NH protons. Complexes 2−4 possess weakly acidic NH protons and undergo D+/NH exchange reactions with D2O or CD3OD. Complexes 2−4 and [Ni(StBu)(RS3)]− (9a,b) also catalyze D2/H+ exchange in [D8]THF/H2O under an elevated pressure of D2 (18 bar), as confirmed by 1H NMR spectroscopy. It is proposed that D2 heterolysis is achieved through attack of the Lewis‐acidic nickel centers and the Brönsted‐basic sulfur atoms at an η2‐D2 ligand. Complexes 9a and 9b are the first sulfur‐only nickel complexes that enable the modeling of the [NiFe] hydrogenase catalyzed D2/H+ exchange reaction. Evidence for labile five‐coordinate [Ni(CO)(L)(RS3)] has been found in the reaction between [Ni(L)(RS3)] complexes and CO. The CO adducts of complexes with nitrogenous ligands L such as N3−, NHPR3 (R = nPr3, Cy3), or NHSPh2 showed rapid consecutive reactions. The reaction between Et4N[Ni(N3)(siS3)] (8b) and CO gave Et4N[Ni(NCO)(siS3)] (10b), whereas reactions between 2−4 and CO afforded only 1a or 1b. Mechanisms are suggested which have the formation of reactive five‐coordinated [Ni(CO)(L)(RS3)] intermediates in common. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

This publication has 36 references indexed in Scilit: