KINETIC AND MECHANISTIC INVESTIGATION OF THE SEQUENTIAL HYDROGENATION OF PHENYLACETYLENE CATALYZED BY RHODIUM(I) PHOSPHINE COMPLEXES OF THE TYPE [RH(ETA(2)-O(2)Z)(PR(3))(2)]

Chelate complexes of the type [Rh(eta(2)-O(2)Z) (PR(3))(2)] (Z = CCH3, CCF3, CtBu, S(O)-p-C6H4-CH3; PR(3) = PiPr(3), PPhir(2), PPh(2)iPr) catalyze the hydrogenation of phenylacetylene in toluene solution at 60 degrees C. Selectivities close to 100% are achieved for the hydrogenation of the alkyne to the alkene in the presence of the acetate and trifluoroacetate complexes [Rh(eta(2)-O(2)CR)(PiPr(3))(2)] (R = CH3 1, CF3 2). However, in other cases the reduction of the C-C double bond is also observed. In general, the selectivity of the hydrogenation reaction depends both on the phosphine and the anionic ligand. For the reduction of PhC=CH catalyzed by 1, the addition of acetic acid leads to a dramatic decrease in the catalytic activity.