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 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 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.
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