Small molecule activation and dehydrogenation of an amine–borane system using frustrated Lewis pairs

Abstract

Cyclic five-membered frustrated phosphane/borane (1) based Lewis pairs containing borole (2a/2b/2c), dihydro-borole (3), and 1,4-azaborine (4) ring are computationally designed. Their catalytic activities for the activation of small molecules like H2, CO2, CH4, H2C = CH2, HC ≡ CH, and dehydrogenation of an amine–borane system are investigated. The effectiveness of FLPs as a catalyst is found in the order like 2c > 2b > 2a > 1 > 3 > 4. The effect of aromaticity, anti-aromaticity, and non-aromaticity is introduced to manipulate the activation barriers for these reactions. In the case of activation of small molecules like ethylene, non-covalent interactions are found to be critical. Upon substituting the hydrogen of borole moiety in FLP 2a by phenyl (2b) and pentafluoro-phenyl (2c), the activation energy of ethylene activation decreases due to the increased dispersion effect. Furthermore, energy decomposition analysis reveals that Pauli interaction and strain energy are dominant factors for ethylene activation.