Reactions of coordinated polyolefins. Sigmahaptotropic reaarangements involving nitrogen migration

(η⁴-Tropone)Fe(CO)₃ reacts with 4-phenyl-triazoline-3,5-dione (NPTD) to give the [3 + 2]- and [4 + 2]-cycloadducts as the initial kinetic products, in a ratio of 3/1. The second order rate constant (at 24°C, in acetone) for the [3 + 2] reaction is 1.56 × 10^-3 M^-1 s^-1 and that for the [4 + 2] reaction 5.10 × 10^-4 M^-1 s^-1 with free activation energies of ΔG^#₁ 21.20 kcal mol^-1 and Δ^#₂ 21.86 kcal mol^-1, respectively. Under thermodynamic conditions an equilibrium mixture is reached containing, in addition to the [3 + 2]- and [4 + 2]-adducts, the [5 + 2]-isomer, with the three products in a ratio of 2/1/39. The kinetic data are consistent with a mechanism in which the [3 + 2]- and the [4 + 2]-adducts equilibrate, with first order constants k₃₄ = 9.8 × 10^-6 s^-1 and k₄₃ = 2.0 × 10^-5 s^-1, respectively, via a [2,2]-sigmahaptotropic rearrangement, while equilibration of the [3 + 2]- and [5 + 2]-isomers takes place with rate constants k₃₅ = 2.9 × 10^-5 s^-1 and k₅₃ = 1.5 × 10^-6 s^-1, respectively, via the [3,3]-sigmahaptotropic rearrangement pathway.