Reactions of coordinated polyolefins. Kinetic studies of a fluxional [2,2]-sigmahaptotropic rearrangement by the spin saturation transfer technique and line shape analysis

The reaction of (3,7,7-trimethylcycloheptatriene)tricarbonyliron with tetracyanoethylene gave an equilibrium mixture of the 2 + 2 and 3 + 2 isomeric adducts in a 2 3 ratio. The rate constants for the interconversion process in CDCl₃ were evaluated by the spin saturation transfer technique, and in CD₃OD by line shape analysis. The activation parameters were ΔH^# 15 kcal/mol, ΔS^# -10 e.u. (CDCl₃), and ΔH^# 20 kcal/mol, ΔS^# + 12 e.u. (CD₃OD), respectively. The kinetic data is consistent with a mechanism in which isomerization proceeds via a single step pericyclic [2,2]-sigmahaptotropic rearrangement.