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.