Activation barriers for β-hydride elimination: systematic study of the single mechanistic step

Abstract

the thermolysis of ¹³C (*) labelled platinum ethyl complexes (cod)Pt(*CH₂CH₃)₂, (cod)Pt(*CH₂CH₃)Cl, and (cod)Pt(*CH₂CH₃)I (cod = cyclo-octa-1,5-diene) was studied at 100–110 °C by quantitative ¹³C n.m.r. spectroscopy, changes in the concentrations of (cod)Pt*(CH₂CH₃)X and (cod)Pt(CH₂*CH₃)X as a function of time allowing direct quantification of the free energy of activation for β-hydride elimination; barriers for (cod)Pt(*CH₂CH₃)X were ΔG^‡= 28.9 ± 0.2 kcal/mol for X =*CH₂CH₃, 29.1 ± 0.2 for X = Cl, and 26.9 ± 0.2 for X = I (1 cal = 4.184 J).