In Silico Activation of CO2, NO2, and SO2 with Light Atom Molecules and Stepwise Conversion of CO2 into Methanol and Water

CO2, NO2, and SO2 can be activated in silico with tailor-made light atom tripodal ligand systems carrying particular numbers of Lewis acidic and basic sites in specific relative orientations. In the calculated EO2-adducts (E=C, N, S), considerable E-O bond elongations of 0.1-0.3 angstrom, decreasing the E=O double bond character, and O-E-O angle alterations, approaching tetrahedral geometry, activate the donor acceptor complexes towards reduction with BH4-. The lone pairs of the P atoms thereby serve as donors towards the central element, C, N, or S, whereas the electron deficient B atoms serve as acceptors. The charge redistribution within the EO2 complex was monitored by a variety of DFT-derived real-space bonding indicators (RSBIs) including bond topologies, non-covalent contact patches, and electron pair basins. For one CO2-complex, the reduction towards methanol and water was conducted via stepwise addition of H- and H+. The most critical steps are the initial CO2 uptake due to potential quenching of the ligand systems in their active state, increasing the kinetic barrier, and the release of methanol and water from the ligand system due to potential ligand poisoning. Unbeneficial side reactions in the stepwise reduction and protonation have to be considered.

Automated summary

In silico activation of CO2, NO2, and SO2 is achieved through tailor-made light atom tripodal ligand systems with specific Lewis acidic and basic sites in specific orientations. This activation involves E-O bond elongations, weakening the E=O double bond, and alterations of O-E-O angles, approaching tetrahedral geometry. Reduction of the donor acceptor complexes with BH4- is facilitated by charge redistribution within the EO2 complex. Stepwise addition of H- and H+ is used for the reduction of CO2 to methanol and water, with potential ligand poisoning and quenching of the ligand systems being important considerations.