Palladium(II) complexes of N,N-dimethylpyrrole-1- and 2-carbothioamides

The reaction of the sodium salt of pyrrole with N,N-dimethylthiocarbamoyl chloride in N,N-dimethylformamide gave N,N-dimethylpyrrole-1-carbothioamide (Hnpt), while the reaction of pyrrole with N,N-dimethylthiocarbamoyl chloride under phase transfer conditions afforded N,N-dimethylpyrrole-2-carbothioamide (Hapt), together with a very small amount of N,N,N′,N′-tetramethylpyrrole-1,2-dicarbothioamide. Hnpt and Hapt were metallated with lithium tetrachloropalladate in methanol to yield PdCl(npt) and PdCl(apt), respectively. Both complexes reacted with tri-n-butylphosphine (PBu₃) and 4-tert-butyl-pyridine (tbp), forming PdCl(npt)(PBu₃), PdCl(npt)(tbp), PdCl(apt)(PBu₃) and PdCl(apt)(tbp). These and some additional complexes were characterized spectroscopically. In the npt complexes, the ligand was cyclopalladated at C(2) of the pyrrole ring, forming a five-membered, organometallic chelate ring accompanied by thioamide sulphur coordination. In the apt complexes, the ligand acted as a bidentate NS chelate, the ring NH proton being deprotonated. The X-ray analysis of PdCl(npt)(PBu₃) and PdCl(apt)(PBu₃) confirmed the coordination modes.