Hydrovinylation of olefins catalyzed by cationic nickel complexes [Ni(2,4,6-Me3C6H2)(CH3CN)P-2]BF4

The hydrovinylation of several olefins and alkynes by the ionic nickel precursor trans-[Ni(2,4,6-Me3C6H2)(CH3CN)(P(CH2Ph)(3))(2)]BF4 in THF solution was studied. The activity of the catalytic system showed strong dependence on the nature of the substrate. Only conjugated diolefins and some strained mono-olefins led to hydrovinylation products with nearly complete conversion. Selectivity was also variable: for norbornene, exo-2-vinylnorbornane (94%) was obtained selectively, whereas isoprene gave a mixture of 9 hydrovinylation compounds. The turnover rate of the reaction at 25 degrees C and 15 bar of initial pressure of ethylene with an olefin/[Ni] ratio of 1000/1 was 4300 h(-1) for norbornene and 30 h(-1) for isoprene. The chiral monodentate phosphines, (cis-myrtanyl)diphenylphosphine and myrtenyldiphenylphosphine, were obtained. The catalytic precursors containing these phosphines were bring tested in the hydrovinylation of styrene and norbornene, and the enantiomeric excess obtained was between 3-7%. Diphenylacetylene was also found to be active in the hydrovinylation reaction; cis- and trans-3,4-diphenyl-1,3-hexadiene, products of a double vinylation of the triple bond were obtained. (C) 1997 Elsevier Science B.V.