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

Abstract

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.

Olefin Metathesis by First‐Row Transition Metals

“…Recently, our group has developed the synthesis of complexes 21 a – e , a new class of compounds, and tested their catalytic activity (Scheme 9). [48] In our study, we selected RCM as a model reaction to examine catalysts′ stability toward ethylene and functional groups tolerance. Products containing a tosylate, an ether, a tertiary amide, a tertiary amine, or an ester were accessed.…”

Synthesis of Vanadium Oxo Alkylidene Complex and Its Reactivity in Ring-Closing Olefin Metathesis Reactions

“…The V1–C1 distance is 1.8432(15) Å and V1–O1 bond is 1.6107(12) Å, that are similar to reported V oxo alkylidene . The large VCSi angle (140.03(9)°) is indicative of α-hydrogen agostic interactions with V center …”

“…V alkylidenes are a promising class of compounds that have shown reactivity in OM, especially in ring-opening metathesis polymerization (ROMP) of cyclic olefins. , Recently, our group reported a method of promoting α-hydrogen abstraction from V trialkyl complexes 4 by using phosphonium hydrochlorides to obtain complexes 5a – e in good yields (Scheme ). Complexes 5a – e are active catalysts in OM and can tolerate various functional groups. Furthermore, it was the first report of V-based catalysts capable of performing ring-closing metathesis (RCM) reactions, besides proposed backbiting reaction during ROMP of cyclopentene, which resembles some elements of RCM.…”

“…Two major pathways are known for catalyst deactivation: β-hydride (β-H) elimination of metallacyclobutane (MCB) and bimolecular decomposition of metal methylidene . It has been shown that the main decomposition pathway of V-based catalysts is β-H elimination. ,, Noteworthy, the structure of V catalysts resembles the structure of Mo and W Schrock complexes. Thus, they are d 0 , high oxidation state complexes with the second multiply bound ligand (imido) in addition to the alkylidene.…”

“…With the complex 12 in hand, we tried our previously optimized conditions to prepare V alkylidenes . Unfortunately, this mostly led to the decomposition of staring material into unidentified paramagnetic compounds.…”