1,5-Dimethyl-1,5-cyclooctadiene and 1,4-dimethyl-4-vinyl-1-cyclohexene are prepared by contacting isoprene with a catalyst obtained by mixing a nickel compound, a reducing agent capable of reducing the nickel to zerovalent nickel, and a trihydrocarbyl phosphite, arsenite or antimonite wherein at least one of the three hydrocarbyl groups is a substituted hydrocarbyl group CF.sub.3 --(CF.sub.2).sub.n C(H)(R)--, in which n.gtoreq.0 and R is an optionally substituted hydrocarbyl group. Only very small amounts of the undesired 1,6-dimethyl-1,5-cyclooctadiene are formed.
On the mechanism of the nickel-catalysed regioselective cyclodimerization of isoprene
作者:P.W.N.M. van Leeuwen、C.F. Roobeek
DOI:10.1016/s0040-4020(01)97949-9
日期:——
similar steric properties the changes in product distribution as a function of the electronic ligand parameter are explained in terms of a gradual change in HOMO-LUMO interactions between Ni and the olefins, with strong π-acidic ligands promoting the head-to-headcoupling of the isoprene molecules. The second step, involving reductive elimination of a cyclodimer from the metal, shows an increasing selectivity