Double C−H Activation Results in Ruthenium Complexes of a Neutral PCP Ligand with a Central Carbene Moiety
2006-10-23T00:00:00Z (GMT) by
Ru complexes of a new neutral PCP pincer ligand containing a central carbene ligand have been prepared (referred to as (P2C) for emphasis). The ligand precursor P2CH2 can be prepared in good yield in two steps from pyrrole, formaldehyde, and chlorodiisopropylphosphine. The reaction between P2CH2 and [(p-cymene)RuCl2]2 in the presence of Et3N cleanly furnishes (P2C)RuHCl. The latter possesses a Y-shaped five-coordinate geometry about Ru, as determined in an X-ray diffraction study. Reactions of (P2C)RuHCl with a series of potential ligands have been examined. Addition of pyridine, MeCN, or ethylene leads to a simple adduct formation and addition of CO leads to coordination of two CO ligands to Ru with concomitant hydride-to-carbene migration, while addition of PMe3 gives rise to both types of products. (P2C)RuHCl is a moderately active precatalyst for transfer hydrogenation of ketones. Addition of phenylacetylene leads to the insertion of the triple bond into Ru−H to give (P2C)Ru(−CPhCH2)Cl. (P2C)RuHCl can be converted to (P2C)RuCl2 by action of an iminium chloride reagent. (P2C)RuCl2 adds one molecule of CO with retention of the carbene moiety, even at elevated temperatures. These results demonstrate the potential of (P2C) as a robust and electronically distinctive ancillary ligand.