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 NiII 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.