Exploring efficient and air-stable d2 Re(v) alkylidyne catalysts: toward room temperature alkyne metathesis

Abstract

Transition metal-catalyzed alkyne metathesis has become a useful tool in synthetic chemistry. Well-defined alkyne metathesis catalysts comprise alkylidyne complexes of tungsten, molybdenum and rhenium. Non-d⁰ Re(V) alkylidyne catalysts exhibit advantages such as remarkable tolerance to air and moisture as well as excellent functional group compatibility. However, the known Re(V) alkylidynes with a pyridine leaving ligand require harsh conditions for activation, resulting in lower catalytic efficiency compared to d⁰ Mo(VI) and W(VI) alkylidynes. Herein, we report the first non-d⁰ alkylidyne complex capable of mediating alkyne metathesis at room temperature, namely, the Re(V) aqua alkylidyne complex Re(CCH₂Ph)(^PhPO)₂(H₂O) (14). The aqua complex readily dissociates a water ligand in solution, confirmed by ligand substitution reactions with other σ-donor ligands. The aqua complex can be readily prepared on a large scale, and is stable to air and moisture in the solid state and compatible with a variety of functional groups. The versatile ability of the catalyst has been demonstrated through examples of alkyne cross-metathesis (ACM), ring-closing alkyne metathesis (RCAM), and acyclic diyne metathesis macrocyclization (ADIMAC) reactions. All in all, this work presents a solution for an efficient and air-stable alkyne metathesis catalytic system based on d² Re(V)-alkylidynes.