Syntheses of ruthenium(II) complexes containing polyphosphine ligands and their applications in the homogeneous hydrogenation

A series of ruthenium(II) complexes of polyphosphine ligands, RuHCl(CO)(etp ) (2), RuHCl(CO)(tdpme) (3) and RuHCl(PP3) (4) [etp PhP(CH2CH2PPh2)(2); tdp me = CH3C(CH2PPh2)(3); PP3 = P(CH2CH2PPh2)(3)] have been prepared from RuHC l(CO)(AsPh3)(3) (1) through typical substitution reactions and characterize d by spectroscopic (IR and H-1 NMR) methods and elemental analyses. These c ompounds have been used as catalyst precursors in the homogeneous hydrogena tion of cyclohexene, cyclohexanone, propanal and 2-cyclohexen-1-one. These polyphosphine Ru(II) complexes show enhanced catalytic activities in compar ison with monodentate or bidentate phosphine or arsine analogues. The selec tivities of compound 3 for substrates have been found to decrease in the or der cyclohexanone > propanal > cyclohexene. In the case of hydrogenation of 2-cyclohexen-1-one, cyclohexanol has been produced by way of cyclohexanone . The catalytic activities are directly proportional to the concentration o f catalysts. The dependence of catalytic activities upon the hydrogen press ure has been also studied. The Arrhenius activation energy of cyclohexanone for compound 3 is found to be E-a= 97.2 kJ mol(-1) and the activation para meters are Delta H-double dagger = 94.0 kJ mol(-1) and Delta S-double dagge r = -0.72 kJ K-1 mol(-1). (C) 1998 Elsevier Science Ltd. All rights reserve d.