(192af) A Theoretical Study of the Activation of Hydrogen and Methane By Frustrated Lewis Pairs

In this work,
we provide a systematic investigation of the activation of the
H-H bond of molecular hydrogen and the C-H bond of methane mediated by intermolecular
Frustated Lewis Pairs. To be specific, we use the
classical sterical encumbered P(t-Me)₃ phosphine as Lewis bases and
two Lewis acids: B(C₆F₅)₃ and Al(C₆F₅)₃.
Calculations
were performed by means of DFT calculations using the dispersion-corrected
ωB97X-D functional in conjunction with the 6-311G(2d,2p), including
toluene as solvent through the PCM-SMD implicit solvent scheme. In all cases,
the activation barriers are larger for methane than for hydrogen. This is due
to a large distortion of the C-H bond to reach the transition state, and
additionally, the distortion of the Lewis acid attains a better interaction
with the σ-bond in methane. Finally, we found that the Lewis acid Al(C₆F₅)₃
has a considerable reduction in the free energy activation barrier for
both hydrogen and methane activation. Thus, this
work demonstrates that, if properly designed, the use of alanes as Lewis acid
can reach high degree of reactivity to methane activation.