Rhodium assisted C-H activation of benzaldehyde thiosemicarbazones and their oxidation via activation of molecular oxygen.
The benzaldehyde thiosemicarbazones are found to undergo oxidation at the sulfur center upon reaction with [Rh(PPh3)(3)Cl] in refluxing ethanol in the presence of a base (NEW. A group of organorhodium complexes are obtained from such reactions, in which the oxidized thiosernicarbazones are coordinated to rhodium as tridentate CNS donors, along with two triphenylphosphines and a hydride. From the reaction with para-nitrobenzaldehyde thiosemicarbazone, a second organometallic complex is obtained, in which the thiosemicarbazone is coordinated to rhodium as a tridentate CNS donor, along with two triphenylphosphines and a hydride. Reaction of the benzaldehyde thiosernicarbazones with [Rh(PPh3)(3)Cl] in refluxing ethanol in the absence of NEt3 affords another group of organorhodium complexes, in which the thiosernicarbazones are coordinated to rhodium as tridentate CNS donors, along with two triphenyiphosphines and a chloride. Structures of representative complexes of each type of complexes have been determined by X-ray crystallography. In all of the complexes, the two PPh3 ligands are trans. All of the complexes show intense MLCT transitions in the visible region. Cyclic voltammetry on these complexes shows a Rh(III)-Rh(IV) oxidation on the positive side of SCE. Redox responses of the coordinated thiosemicarbazones are also displayed by all of the complexes.