Intramolecular C-H Activation Of A Bisphenolate(Benzene)-Ligated Titanium Dibenzyl Complex. Competing Pathways Involving Alpha-Hydrogen Abstraction And Sigma-Bond Metathesis

A titanium dibenzyl complex featuring a ligand with two phenolates linked by a benzene-1.3-diyl group was found to undergo thermal decomposition to give toluene and a cyclometalated dimeric complex. The thermal decomposition followed first-order kinetics and was studied at a number of temperatures to determine the activation parameters (Delta H-double dagger = 27.2(5) kcal/mol and Delta S-double dagger = -6.2(14) cal/(mol K)). Deuterated isotopologues were synthesized to measure the kinetic isotope effects. The complexes with deuterium in the benzyl methylene positions decomposed more slowly than the protio analogues. Isotopologues of toluene with multiple deuteration positions were observed in the product mixtures. These data are consistent with competing alpha-abstraction and sigma-bond metathesis.