Redox-active nickel and cobalt tris(pyrazolyl)borate dithiocarbamate complexes: air-stable Co(ii) dithiocarbamates

Abstract

A series of new cobalt(II) and nickel(II) tris(3,5-diphenylpyrazolyl)borate (Tp^Ph2) dithiocarbamate complexes [Tp^Ph2M(dtc)] (M = Co, dtc = S₂CNEt₂1, S₂CNBz₂2 and S₂CN(CH₂)₄3; M = Ni, dtc = S₂CNEt₂4, S₂CNBz₂5 and S₂CN(CH₂)₄6) have been prepared by the reaction of [Tp^Ph2MBr] with Nadtc in CH₂Cl₂. IR spectroscopy indicates that the Tp^Ph2 ligand is κ³ coordinated while the dithiocarbamate ligand is κ² coordinated. ¹H NMR and UV-Vis spectroscopy are consistent with high spin, five-coordinate metal centres. X-ray crystallographic studies of 1, 3 and 6 confirm the κ³ coordination of the Tp^Ph2 ligand and reveal an intermediate five-coordinate geometry with an asymmetrically coordinated dithiocarbamate ligand. Electrochemical studies of 1–6 reveal a metal centred reversible one-electron oxidation to M(III). Attempted oxidation of [Tp^Ph2Co(dtc)] with [FeCpCp^COMe]BF₄ yields [Co(dtc)₃], Hpz^Ph2 and a further product which may be [Tp^Ph2CoBp^Ph2]. DFT calculations indicate that the low redox potentials in these complexes result from a strongly antibonding M–S σ* HOMO.