Diphenyllead(IV) thiosemicarbazonates and pyrazolonates: Synthesis and characterization

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 PbPh22+ moiety to form homoleptic [PbPh2(L)2] or heteroleptic [PbPh2(OAc)(L)] derivatives. Cyclization did not occur with β-keto amide TSCs and only [PbPh2(TSC)2] or [PbPh2(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–d6 solution, in which they evolve and decompose with time. Additionally, crystals of p-acetoacetanisidide thiosemicarbazone (HTSC10), [PbPh2(OAc)(L5)] · MeOH (HL5 = 2,5-dihydro-3,4-dimethyl-5-oxo-1H-pyrazolone-1-carbothioamide), [PbPh2Cl(L2)] (HL2 = 2,5-dihydro-5-oxo-3-phenyl-1H-pyrazolone-1-carbothioamide), [PbPh2(OAc)(TSC8)] · 2MeOH (HTSC8 = acetoacetanilide thiosemicarbazone), [PbPh2(OAc)(TSC10)] · H2O and [PbPh2(OAc)(TSC11)] · 0.75MeOH (HTSC11 = 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).

Cyclization of thiosemicarbazones derived from β-keto esters and β-keto amides (HTSC) in the presence of diphenyllead(IV) acetate have been studied. The complexes were isolated and characterized by X-ray crystallography and IR and NMR spectroscopy. Only β-keto ester TSCs underwent cyclization to give the corresponding pyrazolone (HL).Figure optionsDownload as PowerPoint slide