Transition State for Intramolecular C-H Bond Cleavage in [(LCu)₂(m-O)₂]²⁺ (L = 1,4,7-Tribenzyl-1,4,7-triazacyclononane)

Cramer, C. J.; Pak, Y.
Theor. Chem. Acc. 2001, 105, 477.

Hybrid quantum mechanical/molecular mechanical electronic structure calculations reveal the transition state for C-H bond cleavage in [(LCu)₂(m-O)₂]²⁺ (L = 1,4,7-Tribenzyl-1,4,7-triazacyclononane) to be consistent with a hydrogen-atom-transfer mechanism from carbon to oxygen. At the MPW1K/DZ-ECP(+)|UFF level, 0 K activation enthalpies for the parent, p-CF3, and p-OH substituted benzyl systems are predicted to be 8.8, 9.5, and 7.8 kcal/mol. Using a one-dimensional Eckart potential to estimate quantum effects on the reaction coordinate, reaction in the unsubstituted system is predicted to proceed with a primary KIE of 22 at 233 K. Structural parameters associated with the H-atom transfer are consistent with the Hammond postulate.

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