Synthesis and Structures of Benzyl- and Amido-Substituted N-Heterocyclic Palladium Carbene Complexes

摘要

The benzyl- and amido-substituted benzimidazolium ligand precursor [Bz-BimH-CH2CONH2]Br (1) was synthesized. Under different conditions, the reactions of this ligand precursor with PdBr2 produced palladium carbene complexes: Pd[(Bz-Bim-CH2CONH2)2Br2] (2), Pd(Bz-Bim-CH2CONH)2 (3), [Pd(Bz-Bim-CH2CONH2)(Py)Br2] (4), or [Pd(Bz-Bim-CH2CONH2)(CH3CN)Br2] (5). These complexes were characterized by NMR, IR, and single-crystal X-ray diffraction analyses. Complex 2 contains two trans rotamers in both the solution and solid state, and a crystal that possesses a trans-anti conformation is confirmed through single-crystal X-ray diffraction analysis. Complex 3 contains two cis-orientated bidentate carbene ligands, and complexes 4 and 5 are mono-carbene complexes. The chelate rings in complex 3 rendered the methylene protons of the amido-substituted diastereotopic, and a long range (six bond) through bond interaction between the carbonyl carbon and the methylene protons of the benzyl-substituent was observed through the HMBC experiment. The catalytic activity studies indicated 4 and 5 are better catalysts in Suzuki-Miyaura coupling reaction.