Structural investigations and reactivity of cobalt(II)–disulfide compounds

Abstract

Controlling the bio-inspired redox conversion of Co(II)–disulfide compounds to their related Co(III)–thiolate complexes is a perplexing task as the factors triggering this reaction are not fully understood. Three disulfide ligands 2,2′–disulfanediylbis(N,N-bis((3,5–dimethyl-1H–pyrazol–1–yl)methyl)ethan-1-amine) (LmpzSSLmpz), 3,3′-disulfanedylbis(N,N-bis(pyridin-2-ylmethyl)propan-1-amine) (LpSSLp), and 2,2′-disulfanediylbis(N,N-bis(6-methylpyridin-2–ylmethyl)ethan-1–amine) (L3SSL3) with different chain lengths and pyrazole or pyridine groups were reacted with cobalt(II) salts and the resulting complexes were studied for their potential to form Co(III)–thiolate complexes. Crystal structures of [Co2(LmpzSSLmpz)(Br)4] [1Br], [Co2(LmpzSSLmpz)(NCS)4] [1NCS], [Co2(LpSSLp)(NCS)4] [2NCS], and [Co2(L3SSL3)(Cl)4] [3Cl] show that generally the disulfide sulfur donors do not coordinate to the cobalt(II) centers, resulting in dinuclear structures containing two 5-coordinate cobalt centers. However, a unique asymmetric structure is found in [1Br] in which one of the sulfur atoms coordinates to one of the cobalt ions. Thiocyanate–induced Co(III)–thiolate formation in the presence of either ligand LmpzSSLmpz or LpSSLp is evidently unsuccessful, as Co(II)–disulfide complexes were obtained. The reaction of the Co(II)–disulfide complexes with 8-quinolinol suggest that redox conversion to Co(III)–thiolate complexes may take place, but the reactions are not clean.