Intramolecular C−H Activation of a Bisphenolate(benzene)-Ligated Titanium Dibenzyl Complex. Competing Pathways Involving α-Hydrogen Abstraction and σ-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 (ΔH‡ = 27.2(5) kcal/mol and ΔS‡ = −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 α-abstraction and σ-bond metathesis.
Additional Information© 2010 American Chemical Society. Received March 31, 2010. Publication Date (Web): July 2, 2010. S.R.G. thanks Scott Virgil of Caltech for synthetic advice. This work was supported by the US DOE Office of Basic Energy Sciences (Grant No. DE-FG03-85ER13431). We thank Lawrence M. Henling and Michael W. Day of Caltech for mounting and solving the crystal structure. The Bruker KAPPA APEXII X-ray diffractometer was purchased via an NSF CRIF:MU award to the California Institute of Technology (No. CHE-0639094).
Supplemental Material - om100253u_si_001.cif
Supplemental Material - om100253u_si_002.pdf