Reactivity of Cobalt(III) Amine-Thiolate Complexes with Terminal and Bridging Thiolate Functions towards Hydrogen Peroxide

Abstract

The reactivity of CoIII amine-thiolate complexes with terminal and bridging thiolate functions towards oxidizing agents has been investigated. The mononuclear CoIII N3S3 complex [CoIII(L1)] (2) (H3L1 represents the hexadentate ligand N,N′,N″-Tris(2-thio-benzyl)-1,1,1 -tris- (aminomethyl)ethane) featuring three terminal thiolate ligands, and the binuclear N3CoIII- (μ-S)3CoIIIN3 complex [CoIII 2(L2)]3+ (4) (H3L2 = N,N′,N″-Tris-[2-thio-3-aminomethyl-5-terrbutyl- benzyl]-1,1,1-tris(aminomethyl)ethane) featuring three bridging thiolates were selected. Hydrogen peroxide was the oxidizing agent. Whereas the thiolato-bridged complex 4 is resistant towards oxidation by hydrogen peroxide, 2 undergoes a ligand-based oxidation reaction to give the amine-sulfinate complex [Co(L1′)] 5, where all three terminal thiolates have been oxidized to sulfinates without gross structural changes of the parent complex 2. In contrast to 4, the cyclic voltammogram of 2 reveals an irreversible oxidation wave at E = +0.52 V vs SCE which can be attributed to a ligand-centered oxidation reaction. 4 and 5 have been structurally characterized by X-ray crystallography.