Benzimidazolin-2-ylidene Complexes of Palladium(II) Featuring a Thioether Moiety: Synthesis, Characterization, Molecular Dynamics, and Catalytic Activities

Six benzimidazolin-2-ylidene palladium(II) complexes with an alkyl-alkyl thioether moiety in the side chain have been synthesized. Due to the hemilabile metal-sulfur bond, the complexes exhibit a marked fluxionality, as evidenced by NMR studies. The thioether moiety is readily displaced by pyridine as well as by another NHC ligand. Hetero(bis)-NHC complexes formally derived from all six chelating mono-NHC complexes have been synthesized as well. For both series of complexes, the catalytic activity has been explored, and they were found to be active catalysts for the intermolecular hydroamination reaction between a sterically hindered aniline and an alkyne in the presence of triflic acid. Furthermore, the complexes catalyze the direct arylation of 1-methylpyrrole.