Syntheses and Characterizations of Pd(II) Complexes Incorporating a N-Heterocyclic Carbene and Aromatic N-Heterocycles

Reaction of the bromo-bridged dimeric monocarbene complex [PdBr2(iPr2-bimy)]2 (1) with various bidentate N-heterocycles afforded novel linear dinuclear Pd(II) complexes {[PdBr2(iPr2-bimy)]2(μ-L)}{μ-L = 4,4‘-bipyridine (2); μ-L = 4,4‘-bipyridylethane (3); μ-L = 4,4‘-bipyridylethylene (4)}. The mononuclear counterpart [PdBr2(iPr2-bimy)(pyridine)] (5) has also been synthesized by reaction of 1 with pyridine. All compounds have been fully characterized by multi-nuclei NMR spectroscopies, FAB mass spectrometry, and X-ray diffraction analyses. Molecular structures of 2−5 show a fixed orientation of the C−H protons in the N-isopropyl substituents toward the metal center, suggesting interesting C−H···Pd preagostic interactions. These interactions are retained in solution as indicated by the large downfield shift of these C−H protons in the 1H NMR spectrum. UV−vis and CV studies revealed that the dinuclear complexes 2−4 have electrochemical behavior similar to that of the mononuclear species 5.