Structural and Reaction Chemistry of Nickel Complexes in Relation to Carbon Monoxide Dehydrogenase: A Reaction System Simulating Acetyl-coenzyme a Synthase Activity

Author

Pericles Stavropoulos, Missouri University of Science and TechnologyFollow
Mark C. Muetterties
Michel Carrié
R. H. Holm

Abstract

A series of nickel complexes [Ni(NS₃ ^R)L]⁺ derived from the tripodal ligand NS₃ ^R = N(CH²CH²SR)₃ (R = i-Pr, t-Bu) has been prepared in order to investigate the stabilities and reactions of certain species potentially relevant to the nickel sites in carbon monoxide dehydrogenase (CODH). Reaction of [Ni(NS₃ ^R)Cl]⁺ with MeMgCl affords [Ni(NS₃ ^R)Me]⁺, which with CO yields [Ni(NS₃ ^R)COMe]⁺. Reaction of [Ni(NS₃ ^tBu)Cl]⁺ with NaBH₄ gives [Ni(NS₃ ^tBu)H]⁺ and the Ni(I) species [Ni(NS₃ ^tBu)]⁺. The hydride complex was obtained with minimal Ni(I) contamination by removal of ethylene from the equilibrium system [Ni(NS₃ ^tBu)Et]⁺/[Ni(NS₃ ^tBu)H]⁺/C₂H₄. Reaction of [Ni(NS₃ ^tBu)]⁺ with CO affords [Ni(NS₃ ^tBu)CO]⁺, whereas [Ni(NS₃ ^tBu)H]⁺ under the same conditions gives Ni(CO)₄ and protonated ligand. All reactions were performed in THF, and all complexes were isolated as BPh₄ ^- salts. This series includes rare examples of the stabilization of Ni-methyl, -acyl, -hydride, and -carbonyl ligands in the absence of nonphysiological (C/P/As) coligands. Trigonal-bipyramidal stereochemistry has been demonstrated for five complexes with L = Cl, Me, COMe, H, and CO by X-ray crystallography. The methyl/acyl transformations with carbon monoxide and the formation in high yield of the thioesters R'SCOMe (R' = Et, CH₂Ph, Ph) upon reaction of [Ni(NS₃ ^R)COMe]⁺ with thiols in THF are two previously undocumented processes mediated at Ni(II) sites lacking non-physiological (C/P/As) ligation. These are relevant to current views of the catalytic reaction cycle of Clostridium thermoaceticum CODH, which is presented. The Ni^II-H and Ni^I-CO species may be pertinent to the CO/CO₂ activity of CODH. Full details of all preparations, other reactions, and structures are presented. This work is an initial attempt to place the reaction chemistry of CODH on a rational basis, and provides some viability for the present reaction cycle of the enzyme.

Recommended Citation

P. Stavropoulos et al., "Structural and Reaction Chemistry of Nickel Complexes in Relation to Carbon Monoxide Dehydrogenase: A Reaction System Simulating Acetyl-coenzyme a Synthase Activity," Journal of the American Chemical Society, vol. 113, no. 22, pp. 8485 - 8492, American Chemical Society (ACS), Oct 1991.

The definitive version is available at https://doi.org/10.1021/ja00022a041

Department(s)

Chemistry

International Standard Serial Number (ISSN)

0002-7863

Document Type

Article - Journal

Document Version

Citation

File Type

text

Language(s)

English

Rights

© 1991 American Chemical Society (ACS), All rights reserved.

Publication Date

01 Oct 1991