Regiospecific metallation in palladium–hydrazone complexes
Abstract
The dimethylhydrazone of pinacolone, ButMeCN1N2Me2, reacts with [PdCl2(NCR)2](R = Me or Ph) to give the complexes [PdCl2(ButMeCNNMe2)2] and [{PdCl2(ButMeCNNMe2)}2], in which the ligands co-ordinate preferentially through the aminic nitrogen, N2. Both species, in solution, carbopalladate regiospecifically on the Me group to give [{[graphic omitted]Me2)But]Cl}2]. In contrast, ButMeCN1N2MePh reacts with palladium to give only the 1 : 1 adduct [{PdCl2(ButMeCNNMePh)}2] in which the ligand co-ordinates preferentially through the iminic nitrogen, N1. This complex is fairly stable in benzene or dichloromethane solution where it slowly decomposes to give only a small amount of the methylpalladated complex [{[graphic omitted]MePh)But]Cl}2]; however, in methanol solution and in the presence of a base, NaO2CMe, it carbopalladates regiospecifically on the But group to give [{[graphic omitted]NMePh)Me]Cl}2]. The reason for different regioselectivity and the relative rate of carbopalladation on the Me and But group (for N2- and N1-co-ordinated hydrazones respectively) are discussed.