Syntheses and catalytic activities of pseudo-pincer and CSC pincer-type Pd(II) complexes derived from benzannulated N-heterocyclic carbenes

Three new dibenzimidazolium salts bearing thioether (B center dot 2HBr, B center dot 2HNO(3)) and sulfoxide (C center dot 2HBr) containing bridges have been synthesized as sulfur-functionalized dicarbene precursors. Palladation of B center dot 2HBr and C center dot 2HBr afforded two new pseudo-pincer complexes cis-[PdBr2(B-kappa C-2)] (1) and cis-[PdBr2(C-kappa C-2)] (2), in which the sulfur-donor remains pendant. Reaction of precursor B center dot 2HNO(3) in the presence of 1 equiv of KBr, on the other hand, yields the first CSC-Pd(II) pincer complex [PdBr(B-kappa(CSC)-C-3)]NO3 (3) bearing two carbene moieties. All three complexes have been fully characterized by multinuclei NMR spectroscopies, ESI mass spectrometry and X-ray diffraction analysis. Their catalytic activities in the Mizoroki-Heck reaction have been evaluated as well.