PREPARATION AND SPECTROSCOPIC CHARACTERIZATION OF (ETA-6-ARENE)-RUTHENIUM(II) TRIFLUOROMETHYLSULFONATES AND OF DINUCLEAR DI-MU-HYDRIDO AND TRI-MU-HYDRIDO (ETA-6-ARENE)RUTHENIUM(II) COMPLEXES - HOMOGENEOUS HYDROGENATION OF CYCLOHEXENE AND 1-HEXENE CATALYZED BY VARIOUS (ETA-6-ARENE)RUTHENIUM(II) COMPLEXES

Treatment of the hexamethylbenzene complex Ru(O2CMe)2(eta-6-C6Me6).H2O in benzene or toluene with H2 (50 bar) at 50-degrees-C gives the dinuclear di-mu-hydrido cation [{Ru(eta-6-C6Me6)}2(mu-H)2(mu-O2CMe)]+ (1), which can be isolated as its red-violet PF6 salt. The analogous mesitylene complex is obtained similarly, whereas under similar conditions the durene complex Ru(O2CMe)2(eta-6-1,2,4,5-C6H2Me4) gives the di-mu-hydrido complex in admixture with the mono-mu-hydrido complex [{Ru(eta-6-C6H2Me4}2(mu-H)(mu-O2CMe)2]+. The tri-mu-hydrido complexes [{Ru(eta-6-arene)}2(mu-H)3]CF3SO3 (arene=C6Me6 (2a), 1,2,4,5-C6H2Me4 (3a)) are obtained by reaction of the (eta-6-arene)ruthenium(II) triflates Ru(OSO2CF3)2(eta-6-arene)-2H2O with 2-propanol and anhydrous Na2CO3, and can be converted into the corresponding PF6 salts 2b, 3b by treatment with NaPF6. The hydroxo complex [{Ru(eta-6-C6Me6)}2(mu-OH)3]Cl.4H2O reacts with 2-propanol to give [{Ru(eta-6-C6Me6)}2(mu-H)3]Cl.4H2O (2c). The monomeric complexes Ru(O2CMe)2(eta-6-C6Me6) and RuCl(O2CMe)(eta-6-C6Me6) in various solvents at 50-degrees-C/1 bar H2 catalyse hydrogenation of cyclohexene to cyclohexane and 1-hexene to hexane much more effectively than the derived dinuclear mu-hydrido complexes. For Ru(O2CMe)2(eta-6-arene), the turnover numbers decrease in the order arene = C6Me6 > 1,3,5-C6H3Me3 > C6H6 and solvent = 2-propanol > ethanol > benzene. It is suggested that monomeric, coordinatively unsaturated hydrido species such as RuH(O2CMe)(eta-6-arene) and RuH2(eta-6-arene) are involved both in catalysis of hydrogenation and in the formation of the dinuclear hydrides. In the case of 1-hexene there is competing isomerization to give predominantly cis-2-hexene; for this process [{Ru(eta-6-C6Me6)}2(mu-H)(mu-O2CMe)2]H(O2CMe)2.H2O is a better catalyst than Ru(O2-CMe)2(eta-6-C6Me6).H2O.