Isomerization of olefins and substituted olefins catalyzed by nickel complexes

The catalytic activity of several Ni (diphosphine)₂/acid homogeneous systems (acid = HCN, CF₃COOH, CCl₃COOH, and H₂SO₄) in the double bond and cistrans isomerizations of olefins has been tested with the following compounds: pentene-1, cis-pentene-2, trans-pentene-2, allyl benzene, allyl cyanide, allyl alcohol. The catalytic efficiency of the Ni(diphosphine)₂/acid systems depends markedly on the nature both of the diphosphine and of the acid employed. When the diphosphine is 1,4-bis(diphenylphosphino)butane and acid = HCN a particularly efficient catalytic system is formed in situ and only in the case of the allyl cyanide is the isomerization limited. During the isomerization of pentene-1, the stereoselectivity in the formation of the cis-2 and trans-2 isomers is quite dependent on the nature of the cocatalyst. It is proposed that a σ-alkyl mechanism is operating in the $\text{Ni(O)}\text{CF}{}_3\text{COOH}$ system and a π-allyl one in the case of $\text{Ni(O)}\text{HCN}$.