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

摘要

The tetradentate bis (dithiolate) ligands 1, 4-bis[(2, 3-disulfanylbenzamido)methyl] benzene H_4L~1 and 1, 7-bis(2, 3-disulfanylbenzamido)heptane H_4L~2 were prepared and converted into the dinuclear titanocene complexes [(TiCp_2)_2(L~1)] 1 and [(TiCp_2)_2(L~2)] 2, respectively. A ligand transfer reaction of 1 and 2 with [NR_4]_2[CoCl_4] (R = Et or Me) led to the formation of the bis(dithiolato)cobaltate (III) complexes [NEt_4][Co(L~1)] 3 [NR_4][Co(L~2)] (R = Et 4a or Me 4b). The anion [Co(L~2)]~- 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(L~2)]_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 (L~3)~(2-).