Ring‐Closing Olefin Metathesis Catalyzed by Well‐Defined Vanadium Alkylidene Complexes

Vanadium‐based catalysts have shown activity and selectivity in ring‐opening metathesis polymerization of strained cyclic olefins comparable to those of Ru, Mo, and W catalysts. However, the application of V alkylidenes in routine organic synthesis is limited. Here, we present the first example of ring‐closing olefin metathesis catalyzed by well‐defined V chloride alkylidene phosphine complexes. The developed catalysts exhibit tolerance to various functional groups, such as an ether, an ester, a tertiary amide, a tertiary amine, and a sulfonamide. The size and electron‐donating properties of the imido group and the phosphine play a crucial role in the stability of active intermediates. Reactions with ethylene and olefins suggest that both β‐hydride elimination of the metallacyclobutene and bimolecular decomposition are responsible for catalyst degradation. Well‐defined vanadium alkylidene complexes catalyze ring‐closing olefin metathesis of various dienes with activity acceptable for routine organic synthesis. The catalytic activity strongly depends on the size and electron‐donating properties of the imido group, as well as the size and σ‐donating properties of the phosphine.