Redox Interconversion between Cobalt(III) Thiolate and Cobalt(II) Disulfide Compounds

Feng Jiang; Maxime A Siegler; Xiaobo Sun; Lin Jiang; Célia Fonseca Guerra; Elisabeth Bouwman

doi:10.1021/acs.inorgchem.8b00549

Redox Interconversion between Cobalt(III) Thiolate and Cobalt(II) Disulfide Compounds

Inorg Chem. 2018 Aug 6;57(15):8796-8805. doi: 10.1021/acs.inorgchem.8b00549. Epub 2018 Jul 19.

Authors

Feng Jiang¹, Maxime A Siegler², Xiaobo Sun³, Lin Jiang¹, Célia Fonseca Guerra^{1

3}, Elisabeth Bouwman¹

Affiliations

¹ Leiden Institute of Chemistry, Gorlaeus Laboratories , Leiden University , P.O. Box 9502, 2300 RA Leiden , The Netherlands.
² Department of Chemistry , Johns Hopkins University , 3400 North Charles Street , Baltimore , Maryland 21218 , United States.
³ Department of Theoretical Chemistry, Amsterdam Center for Multiscale Modeling (ACMM) , Vrije Universiteit Amsterdam , De Boelelaan 1083 , 1081 HV Amsterdam , The Netherlands.

Abstract

The redox interconversion between Co(III) thiolate and Co(II) disulfide compounds has been investigated experimentally and computationally. Reactions of cobalt(II) salts with disulfide ligand L¹SSL¹ (L¹SSL¹ = di-2-(bis(2-pyridylmethyl)amino)-ethyl disulfide) result in the formation of either the high-spin cobalt(II) disulfide compound [Co^II₂(L¹SSL¹)Cl₄] or a low-spin, octahedral cobalt(III) thiolate compound, such as [Co^III(L¹S)(MeCN)₂](BF₄)₂. Addition of thiocyanate anions to a solution containing the latter compound yielded crystals of [Co^III(L¹S)(NCS)₂]. The addition of chloride ions to a solution of [Co^III(L¹S)(MeCN)₂](BF₄)₂ in acetonitrile results in conversion of the cobalt(III) thiolate compound to the cobalt(II) disulfide compound [Co^II₂(L¹SSL¹)Cl₄], as monitored with UV-vis spectroscopy; subsequent addition of AgBF₄ regenerates the Co(III) compound. Computational studies show that exchange by a chloride anion of the coordinated acetonitrile molecule or thiocyanate anion in compounds [Co^III(L¹S)(MeCN)₂]²⁺ and [Co^III(L¹S)(NCS)₂] induces a change in the character of the highest occupied molecular orbitals, showing a decrease of the contribution of the p orbital on sulfur and an increase of the d orbital on cobalt. As a comparison, the synthesis of iron compounds was undertaken. X-ray crystallography revealed that structure of the dinuclear iron(II) disulfide compound [Fe^II₂(L¹SSL¹)Cl₄] is different from that of cobalt(II) compound [Co^II₂(L¹SSL¹)Cl₄]. In contrast to cobalt, reaction of ligand L¹SSL¹ with [Fe(MeCN)₆](BF₄)₂ did not yield the expected Fe(III) thiolate compound. This work is an unprecedented example of redox interconversion between a high-spin Co(II) disulfide compound and a low-spin Co(III) thiolate compound triggered by the nature of the anion.