Investigations of an Unexpected [2+2] Photocycloaddition in the Synthesis of (−)-Scabrolide A from Quantum Mechanics Calculations

It is imperative to develop efficient CO₂ capture and activation technologies to combat the rising levels of deleterious greenhouse gases in the atmosphere. Using Quantum Mechanics methods (Density Functional Theory), we propose and evaluate several metal-free and metal-containing phosphines that provide strong CO₂ binding under ambient conditions. Depending on the electron donating capacity of the phosphine and the ability of the P-bound ligands to hydrogen bond to the CO₂, we find that the CO₂ binding can be as strong as −18.6 kcal/mol downhill, which should be quite adequate for ambient conditions. We explore some modifications of the phosphine to improve CO₂ binding, and we elucidate which chemical descriptors correlate directly with CO₂ binding energy. Specifically, we find that charge accumulation on the CO₂ unit of the CO₂-bound adduct has the greatest correlation with CO₂ binding affinity. Finally, we probe the mechanism for CO₂ reduction to CO and methanol in aqueous media.