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

The reaction of a series of pyridine-appended
imidazolium salts
with Pd­(COD)­Cl2 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.