Chelate complexes of cobalt(III) with bis(dithiolate) ligands: backbone influence on the electronic properties and the reactivity of the metal center

Abstract

The tetradentate bis(dithiolate) ligands 1,4-bis[(2,3-disulfanylbenzamido)methyl]benzene H₄L¹ and 1,7-bis(2,3-disulfanylbenzamido)heptane H₄L² were prepared and converted into the dinuclear titanocene complexes [(TiCp₂)₂(L¹)] 1 and [(TiCp₂)₂(L²)] 2, respectively. A ligand transfer reaction of 1 and 2 with [NR₄]₂[CoCl₄] (R = Et or Me) led to the formation of the bis(dithiolato)cobaltate(III) complexes [NEt₄][Co(L¹)] 3 and [NR₄][Co(L²] (R = Et 4a or Me 4b). The anion [Co(L²)]^– adopts an approximately square-planar co-ordination geometry. Two anions are connected by intermolecular Co–S contacts at the apical position of the metal to form [Co(L²)]₂^2–. In contrast, mononuclear 3 turned out to be unstable with respect to its co-ordination polymer. This phenomenological difference between 3 and 4a, 4b is reflected in the UV-VIS and cyclic voltammetry data of the complexes, which are compared to the data of the corresponding prototype complex tetraethylammonium [bis(3-N-benzylcarbamoylbenzene-1,2-dithiolato)cobaltate(III)] 5 with two unbridged dithiolato-ligands (L³)^2–.