Pyridine-Based PCP-Ruthenium Complexes: Unusual Structures and Metal–Ligand Cooperation

Metal–ligand
cooperation (MLC) by dearomatization/aromatization
provides a unique way for bond activation, which has led to the discovery
of various acceptorless dehydrogenative coupling reactions. However,
most of the studies are based on pincer complexes with a central nitrogen
donor. Aiming at exploration of the possibility of MLC by PCP-type
pincer complexes, we report herein the synthesis, characterization,
structure, and reactivity of pyridine-based PCP-Ru complexes. X-ray
structures and DFT calculations indicate a carbenoid character of
quaternized pyridine-based PCP-Ru complexes. These complexes undergo
dearomatization by direct deprotonation, and the dearomatized complex
can react with hydrogen, alcohols, or nitriles to regain aromatization
via MLC.