(Carboxylato)- and (α-hydroxycarboxylato)-hydridotriphenylphosphineruthenium(II) complexes and their behaviour as homogeneous catalysts for isomerisation and hydrogenation of alkenes
Some new (carboxylato)hydrido(triphenylphosphine) derivatives of ruthenium have been prepared from [RuH2(PPh3)4] or [Ru(CO)H2(PPh3)3] and dicarboxylic acids, HO2C·[CH2]n·CO2H (n= 1–4), and α-hydroxy-acids. When n= 2–4, 2 : 1 (metal : dicarboxylate ligand) hydrido-complexes of formula [{RuH(PPh3)2L}2{O2C·(CH2)n·CO2}](L = PPh3 or CO) are obtained. With malonic acid (n= 1) and α-hydroxy-acids 1 : 1 (metal : carboxylate group) complexes [RuH(O2CCH2CO2H)(PPh3)3], [RuH{O2CCH(OH)R}(PPh3)3](R = H or Ph), and [Ru(CO)H(O2CCH2OH)(PPh3)2] are formed. The (carboxylato)hydrido-complexes are, in benzene solution, effective catalysts for the hydrogenation of alkenes and also for the isomerisation under an inert atmosphere. The activity and selectivity of the different complexes in the isomerisation and hydroisomerisation of pent-1-ene at 50 °C is reported and related to the steric and electronic factors of the carboxylate ligand. With optically active carboxylate ligands, such as (–)-R-phenylglycolate, a low asymmetric induction occurs in the hydrogenation and isomerisation of suitable alkenes.