Heteroleptic Co(III) bisdithiocarbamato-dithione complexes: Synthesis, structure and bonding of [Co(Et₂dtc)₂(R₂pipdt)]BF₄ (R = Me, 1; Ph, 2; pipdt = piperazin-2,3-dithione) complexes

The reaction between the binuclear cobalt complex, [Co2(Et2dtc)5]+, and Me2pipdt and Ph2pipdt ligands has provided almost quantitatively the cobalt tris-chelate heteroleptic complexes [Co(Et2dtc)2(R2pipdt)]BF4 (1 and 2). The molecular structure of 2 shows the metal in a distorted octahedral geometry. The nature of the bonding in these complexes has been elucidated with the support of DFT TD-DFT calculations. Both chelating S,S donors work as weak-field ligands. The comparison of the chemical reactivity for the homoleptic dithiocarbamate complex [Co(Et2dtc)3] and the heteroleptic [Co(Et2dtc)2(Ph2pipdt)]+ derivative shows that the global softness σ is significantly higher in [Co(Et2dtc)2(Ph2pipdt)]+ than in the homoleptic dithiocarbamate complex, due to a reduction of nephelauxetic effect induced by the dithioxamide ligand. The kinetics for the reaction between the reagents in CH2Cl2 has been followed spectrophotometrically as a function of temperature in pseudo-first order conditions with respect to R2pipdt ligands. Kinetic results further support a reaction mechanism involving a one-end reversible dissociation of the [Co2(Et2dtc)5]+ dimer forming a reactive cobalt(III)dithiocarbamato center susceptible to attack by nucleophiles. The effectiveness and versatility of the above reaction is an easy and clean method to provide heteroleptic-dithiocarbamates with a variety of suitable ligands of interest for applicative purposes.</p