Phenyl substituted indenylphosphine ruthenium complexes as catalysts for dehydrogenation of alcohols

Thermal treatment of (1H-inden-3-yl)dicyclohexylphosphinium tetrafluoroborate (1) and (3-mesityl-1H-inden-3-yl)dicyclohexylphosphinium tetrafluoroborate (3) with tBuONa followed by [(η(6)-cymene)RuCl(2))](2) in methanol gave the adduct {(η(6)-cymene)RuCl(2)[(1H-inden-3-yl)PCy(2)]} (6) and {(η(6)-cymene)RuCl(2)[(3-mesityl-1H-inden-3-yl)PCy(2)]} (7), respectively. Thermal treatment of (2-phenyl-1H-inden-3-yl)dicyclohexylphosphinium tetrafluoroborate (4) with tBuONa followed by [(η(6)-cymene)RuCl(2))](2) or RuCl(3)·3H(2)O in methanol gave {Ru[κ(P):(η(6)-2-phenyl-1H-inden-3-yl)PCy(2)]Cl(2)} (8). Whereas (2-mesityl-1H-inden-3-yl)dicyclohexylphosphine (5) reacted with [(η(6)-cymene)RuCl(2))](2) (in toluene) or RuCl(3)·3H(2)O (in ethanol) to afford {Ru[κ(P):(η(6)-2-mesityl-1H-inden-3-yl)PCy(2)]Cl(2)} (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.