Unusual Coordination Mode of Thiosemicarbazone Ligand. Synthesis, Structure, and Redox Properties of Some Ruthenium and Osmium Complexes

Reaction of benzaldehyde thiosemicarbazone (HL-R, 1) with [M(PPh3)3X2] (M = Ru, Os; X = Cl, Br) in ethanol affords complexes of the type [M(PPh3)2(L-R)2] (2), where the L-R ligand is coordinated as a bidentate N,S-donor ligand, forming a four-membered chelate ring. Geometry of the thiosemicarbazone ligand and size of the phenyl group appear to be the two probable factors for the observed coordination mode of the thiosemicarbazone ligand.