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

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 H 2 , CO 2 , CH 4 , H 2 C = CH 2 , 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.