In Situ Generation of Molybdenum-Based Catalyst for Alkyne Metathesis: Further Developments and Mechanistic Insights

Abstract

Molybdenum-based catalysts are among the best candidates to achieve alkyne metathesis. They can be either well-defined carbynes, previously synthesized before their use, but also prepared in situ upon using stable molybdenum carbonyl complexes, or high oxidation state molybdenum salts that need a previous alkylation, both type of precursors being “activated” by hydroxyl-containing compounds such as phenols and silanols. This paper is presenting studies made on these systems, directed towards the knowledge of the reaction paths leading to the active species, and in particular to define the essential role of hydroxyl-containing co-catalyst in the formation of the active species, still ill-defined. From an analysis of the byproducts formed during the reaction, as well as of the initial products, reaction paths to access catalytic carbyne species is suggested, where the ligand environment consists of phenoxy (or siloxy) groups, typically required and identified to lead to alkyne metathesis in the case of well-defined catalysts.