Insight into the relative reactivity of Frustrated Lewis pairs and stable carbenes in activating H-2 and CH4: A comparative computational study

Computational study has been conducted to gain insight into the relative reactivity of stable carbenes (1 and 2) and typical frustrated Lewis pairs (FLPs, 3-6) in activating H-2 and CH4. For the FLP H-2 activations, despite the quite different basicities of the Lewis base components, they have comparable reactivities. The unexpected relative reactivity can be attributed to the following two factors: (i) the vacant carbene C: p(pi) orbital, which is important when carbene works alone but does not participate in the FLP activation; and (ii) the electrostatic interaction between the Lewis base center and the approaching H atom which plays an important role and can either favor or disfavor a reaction. These explanations are also applicable to methane activations. The study brings two messages to the experimentalists for constructing FLPs: (i) it is recommended to use P-and N-centered Lewis bases to construct FLPs for H-2 activation because using more reactive components does not benefit the activation; and (ii) the FLPs are less reactive in activating CH4 than H-2. In addition, using more reactive carbenes as Lewis bases in FLPs does not necessarily benefit the methane activation.