Synthesis of Rhodium–Primary Thioamide Complexes and Their Desulfurization Leading to Rhodium Sulfido Cubane-Type Clusters and Nitriles

Although molecular thioamide complexes
of late-transition metals
have been prepared since 1979, the chemistry of primary thioamide
complexes remains relatively unexplored. To shed light on this area,
we have investigated synthesis, structures, and reactivities of simple
rhodium organometallic complexes with a primary arenecarbothioamide
ligand [Cp*RhCl2{SC­(Ar)­NH2-κ1S}] (Cp* = η5-C5Me5). Intra- and intermolecular hydrogen bonding in the
thioamide complexes is discussed on the basis of 1H NMR
spectroscopy and X-ray analysis. When these rhodium complexes were
treated with a large excess amount of Et3N, desulfurization
of the thioamide ligand took place to give arenecarbonitriles (ArCN)
in high GC yield and the cubane-type cluster [(Cp*Rh)4(μ3-S)4] (3) in good yield as the organometallic
product. Use of a smaller amount (2.4 equiv) of Et3N followed
by treatment with NaBArF4 (ArF =
3,5-(CF3)2C6H3) led to
the isolation of the cationic clusters [(Cp*Rh)4(μ3-S)4]­(BArF4) or [(Cp*Rh)4(μ3-S)4]­(BArF4)2 in low yield. Reaction mechanisms of the desulfurization
of the coordinated thioamides and the formation and one- or two-electron
oxidation of 3 during the desulfurization are discussed.