Promoting productive metathesis pathway and tuning activity of multidentate molybdenum catalysts in alkyne metathesis: A theoretical perspective

Abstract

Molybdenum alkylidyne complexes, including those containing monodentate or multidentate ligands, can catalyze CC bond formation via alkyne metathesis, which is of great importance to organic synthesis and materials chemistry. Herein, to understand the catalyst working mechanism and explore the key parameters determining the catalyst performance, alkyne metathesis catalyzed by molybdenum-based multidentate complexes was systematically investigated using density functional theory calculations. By comparing the desired cross metathesis and undesired polymerization pathways in multidentate and monodentate catalytic systems, the former shows significantly higher activation barrier for alkyne polymerization, resulting in the shutdown of ring-expansion by-product formation. Furthermore, the calculations show that the multidentate ligands taking trigonal-pyramidal geometry play two roles: (1) occupying one of substrate coordination sites to inhibit the polymerization pathway, thus promoting the desired productive pathway; (2) changing the electronic and steric environment to tune catalytic activity. It is worth noting that the metallacyclobutadiene complex with hither plane feature may play a key role in determining the activity of the catalysts. This work thus provides a guiding principle toward high-performance multidentate catalysts for alkyne metathesis.