Transition state for intramolecular C-H bond cleavage in [(LCu)2(mu-O)(2)](2+) (L=1,4,7-tribenzyl-1,4,7-triazacyclononane)

Hybrid quantum mechanical/molecular mechanical electronic structure calcula tions reveal the transition state for C-H bond cleavage in [(LCu)(2) (mu -O )(2)](2+) (L = 1,4,7-tribenzyl-1,4,7-triazacyclononane) to be consistent wi th a hydrogen-atom-transfer mechanism from carbon to oxygen. At the MPW1K/d ouble-zeta effective core potential(e)/univeral force field level, 0 K acti vation enthalpies for the parent, p-CF3, and p-OH substituted benzyl system s are predicted to be 8.8, 9.5, and 7.8 kcal/mol. Using a one-dimensional E ckart potential to estimate quantum effects on the reaction coordinate, rea ction in the unsubstituted system is predicted to proceed with a primary ki netic isotope effect of 22 at 233 K. Structural parameters associated with the hydrogen-atom transfer are consistent with the Hammond postulate.