Rate constants and Arrhenius parameters for H-atom abstraction from Bu3SnH by the 2,2-dimethylvinyl radical in PhMe. Kinetic evidence for an entirely free radical mechanism for the O-directed hydrostannation of alkynols with stannanes and Et3B/O2

Abstract

Using the 2,2-dimethylvinyl radical 6 as a horological calibrant for the α-cyclopropyl-β-tributylstannylvinyl radicals 2a and 13 in PhMe, the k values and Arrhenius parameters for their cyclopropane ring-openings have been estimated by competition kinetics over a 293–353 K temperature range. The high log A values (14.95 and 14.55) for these reactions only satisfactorily align with a unimolecular, β-scissive, E_H1 radical ring-opening being rate-determining, and the radicals 3a (R = Bu) and 14 undergoing H-atom abstraction from the stannane to give 4a and 15. The log A data for these two reactions only endorse a totally free radical mechanism for the O-directed free radical hydrostannation of dialkyl acetylenes with stannanes and Et₃B/O₂. An estimated k_{H-atom abstraction Bu3SnH PhMe 293 K} of 1.96 × 10⁸ mol⁻¹ s⁻¹ is proposed for 6 in PhMe, along with an estimated k_{H-atom abstraction Ph3SnH PhMe 293 K} of 1.36 × 10⁹ mol⁻¹ s⁻¹.