Diphenyllead(IV) thiosemicarbazonates and pyrazolonates: Synthesis and characterization

Abstract

Cyclization of thiosemicarbazones derived from β-keto esters and β-keto amides (HTSC) in the presence of diphenyllead(IV) acetate was explored in methanol solution at room temperature and under reflux. All β-keto ester TSCs underwent cyclization to give the corresponding pyrazolone (HL), which, except in one case, deprotonated and coordinated the PbPh 2 2+ moiety to form homoleptic [PbPh 2(L) 2] or heteroleptic [PbPh 2(OAc)(L)] derivatives. Cyclization did not occur with β-keto amide TSCs and only [PbPh 2(TSC) 2] or [PbPh 2(OAc)(TSC)] thiosemicarbazonates were isolated. The complexes were characterized by IR spectroscopy in the solid state and by 1H, 13C and 207Pb NMR spectroscopy in DMSO– d 6 solution, in which they evolve and decompose with time. Additionally, crystals of p-acetoacetanisidide thiosemicarbazone (HTSC 10), [PbPh 2(OAc)(L 5)] · MeOH (HL 5 = 2,5-dihydro-3,4-dimethyl-5-oxo-1 H-pyrazolone-1-carbothioamide), [PbPh 2Cl(L 2)] (HL 2 = 2,5-dihydro-5-oxo-3-phenyl-1 H-pyrazolone-1-carbothioamide), [PbPh 2(OAc)(TSC 8)] · 2MeOH (HTSC 8 = acetoacetanilide thiosemicarbazone), [PbPh 2(OAc)(TSC 10)] · H 2O and [PbPh 2(OAc)(TSC 11)] · 0.75MeOH (HTSC 11 = o-acetoacetotoluidide) were studied by X-ray crystallography. The complexes, monomers or dimers with almost linear C–Pb–C moieties, are compared with the corresponding derivatives of Pb(II).