Syntheses and reactivity of sulphur rich Re(III) and Tc(III) complexes containing trithioperoxybenzoate, dithiobenzoate and dithiocarbamate ligands

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 MIII(R-PhCS3)2(R-PhCS2), (M = Re; Re1-9; M = 99Tc; Tc1-9). The coordination sphere is entirely filled by sulphur 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 MIII(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.