Syntheses and reactivity of ‘sulfur rich’ Re(iii) and Tc(iii) complexes containing trithioperoxybenzoate, dithiobenzoate and dithiocarbamate ligands

Abstract

Reduction–substitution reactions of [M(O)Cl₄]⁻ (M = Re, ⁹⁹Tc) precursors with an excess of substituted dithiobenzoate ligands (R-PhCS₂)⁻ in dichloromethane/methanol mixtures afford a series of six-coordinated neutral mixed-ligand complexes of the type M^III(R-PhCS₃)₂(R-PhCS₂) (M = Re; Re1–9; M = ⁹⁹Tc; Tc1–9). The coordination sphere is entirely filled by sulfur donor atoms, and the complexes adopt a distorted trigonal prismatic arrangement, as assessed by the X-ray crystal structure analysis of Re(4-Me-PhCS₃)₂(4-Me-PhCS₂), Re2. These compounds show sharp proton and carbon NMR profiles, in agreement with the diamagnetism typical of low spin d⁴ trigonal prismatic configurations. The red-ox processes involve reduction of the metal from Re(V) to Re(III) and oxidation of dithiobenzoate to trithioperoxybenzoate. M2–9 complexes contain a substitution-inert [M(R-PhCS₃)₂]⁺ moiety including the metal and two trithioperoxybenzoate fragments, while the third dithiobenzoate ligand is labile. The latter is efficiently replaced by reaction with better nucleophiles such as diethyldithiocarbamate giving a further class of mixed ligand complexes of the type M^III(R-PhCS₃)₂(Et₂NCS₂) (M = Re; Re10–18; M = ⁹⁹Tc; Tc10–18), which retain the trigonal prismatic arrangement, as determined by the X-ray analyses of the representative compounds Re(PhCS₃)₂(Et₂NCS₂), Re10 and ⁹⁹Tc(PhCS₃)₂(Et₂NCS₂), Tc10.