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

Article abstract of DOI:10.1016/0277-5387(94)00346-G

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 tetrachloropalladate(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 (PBu3) 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-CH3 groups and one benzene ring hydrogen atom. This should result in disfavoured benzene ring cyclopalladation of N,N-dimethylthiobenzamide (Hbt) with lithium tetrachloropalladate(II) and induce N-CH3 cyclopalladation.