Cyclometallation of N, N-dimethyl-2-bromothiobenzamide and some related thioamides with palladium(0) and palladium(II)

Abstract

N, N-Dimethyl-2-X-thiobenzamide [XCl (abbreviated as Hcbt) and Br (Hbbt)] and N, N-dimethyl-2-(2-bromophenyl) thioacetamide (Hbpt) were cyclopalladated at one of the N-methyl groups upon reaction with lithium tetrachloroparalladate(II), while oxidative addition took place at the aryl-halogen bond of Hbbt, Hbpt and N, N-dimethyl-2-iodothiobenzamide (Hibt) upon reaction with bis(dibenzylideneacetone)palladium(0). The reaction products, and their tri- n-butylphosphine (PBu 3) and 4-tert-butylpyridine (tbp) derivatives, were characterized by IR and NMR spectroscopies. All the complexes were composed of a palladathiaheterocycle with sulphur coordination of a thioamide group. The structure of ( N, N-dimethylthiobenzamido) ( N, N-diethyldithiocarbamato)palladium(II) was determined by X-ray analysis. There is steric hindrance between one of the NCH 3 groups and one benzene ring hydrogen atom. This should result in disfavoured benzene ringccyclopalladation of N, N-dimethylthiobenzamide (Hbt) with lithium tetrachloropalladate(II) and induce NCH 3 cyclopalladation.