DFT Study on origin of chemoselectivity and difference of bases in catalytic activity in Ag(I)/base-catalyzed CO₂ carboxylation and cyclization.

Abstract

The mechanisms of AgOAc-catalyzed CO₂ incorporation into conjugated ynones are studied using density functional theory (DFT) calculations to explore the selectivity of reaction (5-exo-dig P1 versus 6-endo-dig P2) and to understand the effects of bases (MTBD versus TMG versus DMAP) on the reactions. The bases have the function of proton-shuttle, assisting the transfer of H1 (H2) from C4 (C4) to C1 (O1) by the four-step proton-transfer strategy. More importantly, the differences of base strength are revealed to be the primary factor that determines the catalytic activities of MTBD, TMG, and DMAP, and the order of catalytic activity is MTBD > TMG > DMAP, which does match with the increased trend of base strength MTBD > TMG > DMAP. Moreover, the selectivity of Ag(I)-catalyzed reaction is controlled via the intramolecular cyclization to selectively generate 5-exo-dig P1, which could be reasonably explained by the analysis of electronic interactions and bond lengths on the base of theoretical calculations. In a word, the studies provide indispensable understanding for the transition-metals catalyzed CO₂ conversion with assistance of bases to synthesize various high-value chemicals.