Computational Details
All theoretical calculations were carried out by using theGaussian09 suit of
program.63 Structures
of all stationary points, including the reactants, products, transition
states and intermediates, were fully optimized by using the M06-2X
functional64-66 and the
6-31G(d, p) basis
set67,68under gas phase (Level A ). The harmonic frequency calculations
were performed at the same level with the temperature set as 303.15 K
and the pressure as 1 atm according to the experimental report. All
reactants, products, and intermediates were corroborated to have no
imaginary frequency while each transition state to have one and only one
imaginary frequency. The same level of intrinsic reaction coordinate
calculations
(IRC)69,70were carried out to confirm each transition state linked the expected
reactant and product. Based on the optimized structures, all energies
were refined by single-point calculations at the M06-2X/6-311++G(d,
p)71 level of theory,
with the solvent effects of DMSO simulated by Truhlar’s
SMD72,73model (Level B ). All energies discussed in this paper were
calculated by adding the single-point energies obtained at Level
B to the thermal corrections of the Gibbs free energies calculated atLevel A .