Theoretical insights into the mechanism and selectivities of rhodium/amine dual catalysis in alkyne–cyclopropene reassembly reactions

Abstract

Rhodium/amine dual catalysis has recently emerged as a powerful strategy for C–C bond reconstruction between conjugated alkynes and cyclopropenes, offering new opportunities for complex molecule synthesis. In this work, we performed detailed density functional theory (DFT) investigations to elucidate the full reaction mechanism and the selectivity-determining factors underlying this cascade transformation involving cyclopropenes. Our mechanistic study reveals significant deviations from the previously proposed experimental mechanism, most notably that the reaction proceeds via a cooperative rather than a relay-type mechanism, with rhodium and amine catalysts acting synergistically throughout the catalytic cycle. ETS-NOCV analyses uncover a dual role of the Rh₂(esp)₂ complex: it assists amine-mediated alkyne activation by promoting σ-character development and through-metal delocalization, and it plays a crucial role in the cyclopropane ring-opening and water-addition steps by stabilizing transition states through substantial substrate-to-Rh charge transfer and strengthened Rh–C bonding. GRI and FMO analyses further reveal that dimethylamine electronically activates the alkyne substrate, enhancing its nucleophilicity and facilitating a more accessible reaction pathway. In addition, ligand- and amine-dependent variations in yields are well explained by ECDA and distortion–interaction analyses, which reveal that electron-rich Rh ligands and less sterically hindered amines enhance catalytic efficiency by promoting charge transfer and minimizing structural distortion in the transition state. Taken together, these findings provide valuable design principles for developing next-generation dual catalytic systems for selective and efficient C–C bond transformations.