A New Type of Palladium-Pincer Complexes Generated via Hydrolytic Ring-Opening of Imidazole-2-ylidenes

摘要

The reaction of a series of pyridine-appended imidazolium salts with Pd(COD)Cl_2 in the presence of KOtBu as base led to hydrolytic ring-opening followed by a new type of pincer tridentate (N,C,O) bonding of the in situ generated formamide-based new ligands toward the metal center. This unprecedented type of bonding resulted from a vinylic C?H activation by palladium stabilized with coordination from the pyridine nitrogen and aldehyde oxygen donors in a pincer fashion. The new stable, square-planar palladium(II) complexes (1?3) were characterized by 1D and 2D NMR spectroscopic and high-resolution mass spectrometric (HRMS) methods. The single-crystal X-ray structure of a representative complex (2) confirmed the above interesting bonding features.