Energy Decomposition Analysis of Lewis Acid/Base Adducts and Frustrated Lewis Pairs: The Use of E_Orb/E_Steric Ratios as a Reaction Parameter

The nature of bonding in classical adducts and frustrated Lewis pairs (FLPs) of oxorhenium and nitridorhenium complexes with B(C6F5)3 was investigated computationally (B3PW91-D3). These studies have revealed that the primary noncovalent interaction (NCI) in the FLPs involves lone pair/π interactions between the terminal M≡X bond and the aromatic C6F5 ring in B(C6F5)3. Energy decomposition analyses on classical adducts and FLPs reveal that these species can be defined by the ratio (EOrb/ESteric) of covalent-to-noncovalent contributions to the total interaction energy, EInt. This type of analysis reveals that values for FLPs exist in a narrow range (1.2-2.5), with values for adducts significantly outside this range. The application of this method to other main-group combinations of Lewis acids and bases that have been shown to exhibit FLP reactivity yields similar results. These data suggest that similar NCIs are present in both transition-metal and main-group FLPs, especially where Lewis acids such as B(C6F5)3 are utilized.