Phenyl substituted indenylphosphine ruthenium complexes as catalysts for dehydrogenation of alcohols

Abstract

Thermal treatment of (1H-inden-3-yl)dicyclohexylphosphinium tetrafluoroborate (1) and (3-mesityl-1H-inden-3-yl)dicyclohexylphosphinium tetrafluoroborate (3) with tBuONa followed by [(η⁶-cymene)RuCl₂)]₂ in methanol gave the adduct {(η⁶-cymene)RuCl₂[(1H-inden-3-yl)PCy₂]} (6) and {(η⁶-cymene)RuCl₂[(3-mesityl-1H-inden-3-yl)PCy₂]} (7), respectively. Thermal treatment of (2-phenyl-1H-inden-3-yl)dicyclohexylphosphinium tetrafluoroborate (4) with tBuONa followed by [(η⁶-cymene)RuCl₂)]₂ or RuCl₃·3H₂O in methanol gave {Ru[κ(P):(η⁶-2-phenyl-1H-inden-3-yl)PCy₂]Cl₂} (8). Whereas (2-mesityl-1H-inden-3-yl)dicyclohexylphosphine (5) reacted with [(η⁶-cymene)RuCl₂)]₂ (in toluene) or RuCl₃·3H₂O (in ethanol) to afford {Ru[κ(P):(η⁶-2-mesityl-1H-inden-3-yl)PCy₂]Cl₂} (9). The molecular structures of complexes 6, 8 and 9 have been determined by single-crystal X-ray diffraction analysis. In addition, complexes 8 and 9 have been found to catalyze the acceptorless dehydrogenation of alcohols in toluene. 9 displayed high activity and different substrates, including cyclic and linear alcohols, were efficiently oxidized to ketones by using 2.0 mol% of catalyst.