Cyclopentadienone Iridium Bipyridyl Complexes: Acid-Stable Transfer Hydrogenation Catalysts

• Published in: Organometallics Vol. 42; no. 15; pp. 1849 - 1853
• Main Authors: Marron, Daniel P., Galvin, Conor M., Waymouth, Robert M.
• Format: Journal Article
• Language: English
• Published: American Chemical Society 14.08.2023
• ISSN: 0276-7333; 1520-6041
• DOI: 10.1021/acs.organomet.3c00266

The synthesis, structure, and reactivity of a series of cyclopentadienone and hydroxycyclopentadienyl 4,4′-dimethyl-2,2′-bipyridine (dmbpy) iridium complexes, (C5Tol2Ph2O)­(dmbpy)­IrCl (1), [(C5Tol2Ph2OH)­(dmbpy)­IrCl]­[OTf] (2), (C5Tol2Ph2O)­(dmbpy)­IrH (3), and [(C5Tol2Ph2OH)­(dmbpy)­IrH]­[OTf] (4), are described. The Ir­(I) complexes 1 and 3 are active catalyst precursors for the transfer hydrogenation of aldehydes, ketones, and N-heterocycles with HCO2H/Et3N under mild conditions. Model studies implicate the cationic iridium hydride 4 as a key intermediate, as 4 reacts readily with acetone to generate isopropanol. Selectivity over hydrogenation of alkenes is enhanced compared to other Shvo-type catalysts, and only modest CC hydrogenation is observed when adjacent to polarizing functional groups. Catalytic hydrogenation likely proceeds by a metal–ligand bifunctional mechanism similar to related cyclopentadienone complexes.