DFT calculations were also undertaken on the mechanism of the vinylic C-H activation of styrenes. A low energy pathway was identified involving the direct intramolecular C-H activation of the bound styrene in 3a (Figure ). The mechanism is initiated through a concerted but asynchronous addition of the C=C double bond to 1. This first step has a low activation barrier of ΔG ‡ 298K = 15.8 kcal/mol (TS-1a) and is moderately exergonic by -2. TS-3a appears to be a highly asynchronous transition state near the boundary between a concerted and a stepwise mechanism (vide infra). The low imaginary frequency (-92.3 cm -1 ) of TS-3a refers to the reorientation of the bound alkene in which the α-C is moving away from the Al center while the β-C is transferred from Fe to Al. There is no stationary point for the actual cleavage of the C-H bond which occurs along the intrinsic reaction coordinate en route to INT-4a (see Intrinsic Reaction Coordinate in Figure ). The (E)-stereospecific nature of the C-H activation is a direct consequence of the orientation of the substituents in the transition state TS-3a (vide infra).