MECHANISM OF THE HYDROGENATION OF PHENYLACETYLENE CATALYZED BY [IR(COD)(ETA(2)-IPR2PCH2CH2OME)]BF4

The synthesis of the mononuclear complexes of formulas IrCl(COD)(iPr2PCH2CH2OMe) (1) (COD = 1,5-cyclooctadiene), IrCl(COD)(iPr2PCH2CH2NMe2) (2), [Ir(diolefin) (eta2-iPr2PCH2-CH2OMe)]BF4(diolefin = COD (3), TFB (5) (TFB = tetrafluorobenzobarrelene)), [Ir(diolefin)-(eta2-iPr2PCH2CH2NMe2)]BF4 (diolefin = COD (4), TFB (6)), [IrH(C2Ph)(COD)(eta2-iPr2PCH2-CH2OMe)]BF4 (7), and [IrH2(COD)(eta2-iPr2PCH2CH2OMe)BF4 (8) are described. The X-ray crystal structure of 3 has been determined (monoclinic space group P2(1)/n (No. 14) with a = 8.466(3) angstrom, b = 9.004(3) angstrom, c = 27.052(13) angstrom, beta = 97.71(2)-degrees, and Z = 4). 3 is found to be a very active and highly selective catalyst for the hydrogenation of phenylacetylene to styrene. Although the hydrido-alkynyl-diolefin compound 7 is the main species under catalytic conditions, the reaction proceeds via the dihydrido-diolefin intermediate 8 according to the following set of reactions: 8 + H-2 half arrow right over half arrow left [IrH(CH=CHPh)(COD)(eta2-iPr2PCH2CH2OMe)]BF4 (9) and 9 + H-2 --> 8 + PhCH=CH2 where the reaction between 9 and molecular hydrogen is the rate-determining step. The catalytic activity of 3-6 in the hydrogenation of olefins is also reported.