Rhenium(I) carbonyl complexes of bis(N,N-diethylamino)carbeniumdithiocarboxylate, a novel inner-salt type sulfur donor ligand. Spectroscopic and structural studies

The reaction of the inner-salt SS donor ligand, bis(N,N-diethylamino)carbeniumdithiocarboxylate, Et4L, with [Re(CO)5Cl] afforded a red colored dinuclear rhenium(I) complex [Re2(CO)6(μ-Cl)2(μ-(Et4L)] in excellent yield, along with the mononuclear complex [Re(CO)3(Et4L)Cl]. The corresponding reactions of the ligand with [Re(CO)5Br] give only the mononuclear analogue, [Re(CO)3(Et4L)Br]. All the complexes were structurally characterized. The X-ray structure of the dinuclear complex revealed that two facially coordinated {Re(CO)3}+ moieties are chelated by the novel inner-salt type sulfur donor ligand and are bridged by two chloride ligands. The ReCO bonds, trans to the S donors of the ligand are longer than the other ReCO bonds, evidently due to the strong trans influence of the ligand. IR and 1H and 13C NMR data indicate that all the complexes are substantially stable in solution. The dinuclear complex displays metal based and ligand based quasi-reversible oxidation and reduction couples, respectively, whereas the mononuclear complexes are unstable under the same electrochemical conditions.