Diene reactions. Part 1.—Ligand exchange and π-allylic complex formation associated with the system Ni{P(OPh)3}4+ isoprene + CCl4

Abstract

We have shown that reaction between tetrakis(triphenyl phosphite)nickel(0)(Ni(tp)₄), isoprene (is) and carbon tetrachloride leads to the formation of an orange-coloured π-allylic Ni^II derivative, without free-radical generation. The first stage, ligand exchange between Ni(tp)₄ and (is) leading to a weak Ni⁰ complex (I), is analogous to the corresponding reactions with methyl methacrylate and styrene, but the bonding is weaker in the case of isoprene. Complex (I) then reacts with CCl₄ in two distinct stages, the first, an addition reaction occurring effectively instantaneously, yielding a species which subsequently rearranges intramolecularly and relatively slowly into the π-allylic complex.

Detailed kinetic analyses of the ligand exchange and the overall reaction have been carried out, good agreement between results calculated from the proposed mechanism and observation being obtained.