Reactions of thiosemicarbazones derived from p-keto amides and p-keto esters with Zn(II) and Cd(II) acetates:influence of metal,substitution,reagent ratio and temperature on metal-induced cyclization

摘要

Zinc(II) and cadmium(II) acetates were reacted in methanol under various experimental conditions with thiosemicarbazones derived from P-keto amides or P-keto esters (HTSC).Some of these reactions afforded thiosemicarbazonate complexes [M(TSC)_2] with IR and NMR spectra compatible with N,S-coordination,but most gave complexes [ML_2],where HL is a substituted 2,5-dihydro-5-oxo-1H-pyrazole-l-carbothioamide resulting from cyclization of the HTSC.Some of these pyrazolonates and two of the HL ligands were studied by X-ray diffractometry,and their structures are discussed.Surprisingly,the reactions of zinc(II) acetate with HTSC in 1 :1 mol ratio usually gave a third,previously unreported type of complex with a dideprotonated ligand,[Zn(L - H)],which was also formed when [ZnL_2] and Zn(OAc)_2 interacted at room temperature in 1 :1 mol ratio.These L - H complexes are highly insoluble in all common solvents,which hinders their characterization but suggests that they are polymeric in nature.