The preparation and reactions of hydridochlorotris(triphenylphosphine)ruthenium(II) including homogeneous catalytic hydrogenation of alk-1-enes

Abstract

The complex hydridochlorotris(triphenylphosphine)ruthenium(II) as a benzene solvate, RuClH(PPh₃)₃,C₆H₆, has been obtained by the interaction of the dichloride, RuCl₂(PPh₃)₃, with molecular hydrogen at ambient temperature pressure in the presence of a base such as triethylamine; other preparative methods are described. The corresponding bromide, RuBrH(PPh₃)₃,C₆H₆, has been prepared. From the chloride by interaction with norbornadiene and 2,2′-bipyridyl, the complexes RuClH(C₇H₈)(PPh₃)₂ and [RuClH(bipyr)(PPh₃)₂]₂ respectively have been obtained; the complex RuH₂(CO)(PPh₃)₃ has also been prepared. The complex RuClH(PPh₃)₃ is the most active catalyst yet discovered for the homogeneous hydrogenation of alk-1-enes in benzene or toluene solution. The interaction is highly specific and rates for other types of alkene are slower by a factor of at least 2 × 10³. The inherent difficulties of the system however preclude detailed kinetic study and it is shown that slow poisoning of the catalyst occurs under hydrogenation conditions. N.m.r. studies of the hydrido-complex and its deuteride have allowed hydrogen atom exchange studies to be made. Isomerisation of alkenes is studied. The slow exchange between molecular hydrogen and the α-proton of a phenyl group on the phosphine is demonstrated.