While formation of a frustrated Lewis pair (FLP) depends largely on the steric bulk of the substituents, its efficacy at activating a substrate depends on the Lewis acidity and basicity of the components. These parameters determine the field polarization, and in turn the �activation ability�, within the FLP cage. Investigation of systems containing Lewis acids of varied acidity that can be FLP components is thus worthy. Cyclic phosphenium cations are expected to act as particularly strong Lewis acids owing to the presence of the positive charge. However, identifying appropriately bulky and electron-withdrawing substituents is critical to the development of phosphenium-based FLPs owing to their vicinal rather than geminal positioning. We have discovered computationally that 2,4,6-trimethylphenyl and perfluorophenyl substituents do not adequately shield the cationic phosphorus atom from rather bulky phosphines, but poly(trifluoromethyl)phenyl substituents do. We will describe computational studies of cyclic phosphenium cations of sufficient bulk to form FLPs. Particular focus will fall on tris-(2,6-bis-trifluoromethylphenyl)borane/phosphine and tris-(2,4,6-tris-trifluoromethylphenyl)borane/phosphine pairs, which exhibit P�P distances similar to the B�P distances in archetypal FLPs, and intriguing energetics in their activation of small molecules such as H2 and CO2.

Computational studies of frustrated Lewis pairs based on cyclic phosphenium cations

248th National Meeting (2014)

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