REACTIONS OF COORDINATED POLYOLEFINS. SIGMAHAPTOTROPIC REARRANGEMENTS INVOLVING NITROGEN MIGRATION

Article abstract of DOI:10.1016/0022-328X(87)87012-2

(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 deg C, in acetone) for the <3+2> reaction is 1.56E-3 M^-1 s^-1 and that for the <4+2> reaction 5.10E-4 M^-1 s^-1 with free activation energies of Δ₁^* 21.20 kcal mol^-1 and Δ₂^* 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 <4+2>-adducts equilibrate, with first order constants k₃₄=9,8E-6 s^-1 and k₄₃=2.0E-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=2.9E-5 s^-1 and k₅₃=1.5E-6 s^-1, respectively, via the <3,3>-sigmahaptotropic rearrangement pathway.