Model Complexes for the Ni p Site of Acetyl Coenzyme A Synthase/Carbon Monoxide (CO) Dehydrogenase: Structure, Electrochemistry, and CO Reactivity

• Published in: Inorganic chemistry 2018-11, Vol.57 (21), p.13713-13727
• Main Authors: Bhandari, Anirban, Chandra Maji, Ram, Mishra, Saikat, Kumar, Akhilesh, Barman, Suman Kumar, Das, Partha Pratim, Ghiassi, Kamran B, Olmstead, Marilyn M, Patra, Apurba K
• Format: Article
• Language: English
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/acs.inorgchem.8b02276

Aliphatic thiolato-S-bridged tri- and binuclear nickel(II) complexes have been synthesized and characterized as models for the Ni site of the A cluster of acetyl coenzyme A synthase (ACS)/carbon monooxide (CO) dehydrogenase. Reaction of the in situ formed N S donor ligands with [Ni(H O) ](ClO ) afforded the trinuclear complexes [Ni{(L ) Ni} ](ClO ) ·CH CN (1·CH CN) and [Ni{(L ) Ni} ](ClO ) ·5H O (2·5H O) following self-assembly. Complexes 1 and 2 react with [Ni(dppe)Cl ] and dppe [dppe = 1,2-bis(diphenylphosphino)ethane] to afford the binuclear [Ni(dppe)Ni(L ) ](ClO ) ·2H O (3·2H O) and [Ni(dppe)Ni(L ) ](ClO ) ·0.75O(C H ) [4·0.75O(C H ) ], respectively. The X-ray crystal structures of 1-4 revealed a central Ni S moiety in 1 and 2 and a Ni P S moiety in 3 and 4; both moieties have a square-planar environment around Ni and may mimic the properties of the Ni site of ACS. The electrochemical reduction of both terminal Ni ions of 1 and 2 occurs simultaneously, which is further confirmed by the isolation of [Ni{(L ) Ni(NO)} ](ClO ) (5) and [Ni{(L ) Ni(NO)} ](ClO ) (6) following reductive nitrosylation of 1 and 2. Complexes 5 and 6 exhibit ν at 1773 and 1789 cm , respectively. In the presence of O , both 5 and 6 transform to nitrite-bound monomers [(L )Ni(NO )](ClO ) (7) and [(L )Ni(NO )](ClO ) (8). The nature of the ligand modification is evident from the X-ray crystal structure of 7. To understand the origin of multiple reductive responses of 1-4, complex [(L ) Ni](ClO ) (9) is considered. The central NiS part of 1 is labile like the Ni site of ACS and can be replaced by phenanthroline. The treatment of CO to reduce 3 generates a 3 -(CO) species, as confirmed by Fourier transform infrared (ν = 1997 and 2068 cm ) and electron paramagnetic resonance ( g = 2.18, g = 2.13, g = 1.95, and A = 30-80 G) spectroscopy. The CO binding to Ni of 3 is relevant to the ACS activity.