Unexpected differences in the reactivity between MPh 2Cl 2 (M = Pb or Sn) and benzil bis(thiosemicarbazone). X-ray crystal structure of benzil bis(thiosemicarbazonate)lead(II)

Abstract

The differences in the reactivity of diphenyllead and diphenyltin dichloride with benzil bis(thiosemicarbazone) LH 6 are explored. The reaction of PbPh 2Cl 2 afforded the complex [Pb(LH 4)] 1, containing the ligand doubly deprotonated and without the phenyl groups bonded to the metal. The reaction with SnPh 2Cl 2 in the absence of solvent yielded the complex [Sn(LH 4)Cl 2] 2. The lead(II) complex, also obtained by the reaction with lead(II) nitrate, was formed by a redistribution of the organolead derivative followed by a reductive elimination reaction, while the tin one was formed by a dephenylation process. Reactions in solution of the organotin derivative are complicated and depending on the working conditions different compounds could be isolated: the organostannoxane [Sn 2Ph 4ClO(OH)] 2, which was confirmed by X-ray crystallography, or a complex containing a triazine-3-thione ligand, formed by the loss of one of the thiosemicarbazone arms with subsequent cyclisation. The compounds were characterized by IR, mass spectrometry, 1H, 13C and 119Sn NMR spectroscopy in solution and in the solid state. The structure of [Pb(LH 4)] has been studied by X-ray diffraction and the ligand acts as a N 2S 2 planar bideprotonated ligand, with the lead(II) ion localized 1.3858 Å over this plane.