CO2 adducts of Lewis acid–base pairs (LBCO2LA; LB = PMe3, NHC and LA = AlH3, AlCl3, BH3) − analogous to carboxylic acids and their derivatives

Abstract

The relationship between the structure and bonding of two different classes of molecules helps to understand and correlate their physiochemical activity. Here, we report the structure-bonding analogy between CO₂ adducts of a Lewis acid (LA)–Lewis base (LB) pairs, LBCO₂LA (LB = PMe₃ and NHC; LA = AlH₃, AlCl₃ and BH₃) and carboxylic acids and their derivatives, RCO₂R′ (R, R′ = alkyl, H) by quantum mechanical calculations. The direction of charge flow in LBCO₂LA is from LB to LA, whereas the reverse direction of charge flow (R′ to R) is observed for RCO₂R′ leading to a formally negatively charged CO₂ group (²A₁) in both systems. This negatively charged bent CO₂ group plays a deterministic role towards its bonding interaction with other fragments. The bonding analysis by the EDA-NOCV method indicates that both the LB and R groups form an electron sharing bond with the carbon atom of the bent CO₂ fragment, whereas both LA and R′ form a donor–acceptor interaction with the oxygen atom. Our analysis suggests that the CO₂ adducts of the Lewis acid (LA)–Lewis base (LB) pairs, LBCO₂LA, can be considered as inorganic analogues of carboxylic acids and their derivatives, RCO₂R′.