Decomposition of Vanadium(V) Alkylidenes Relevant to Olefin Metathesis
Decomposition of Vanadium(V) Alkylidenes Relevant to Olefin Metathesis
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DOI：
10.1021/acs.organomet.0c00610
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发表时间：
2020-11-09
期刊：
影响因子：
2.8
通讯作者：
Zavalij, Peter Y.
中科院分区：
文献类型：
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作者：
Farrell, Wesley S.;Greene, Christine;Zavalij, Peter Y.
钒烷基烷烃是环烯烃开环复分解聚合的高效引发剂；然而，由于催化剂的分解，试图扩大它们在交叉复分解中的应用一直没有成功。详细了解分解反应是指导未来催化剂设计的必要条件。在此，我们证明了-氢化物消除是交叉复分解过程中的主要分解途径。两种催化剂分离得到的钒分解产物[n -2,6-(CH3)(2)C6H3-](OC6Cl3)[P(CH3)(3)](2)VCl（10）和[n -2,6-(CH3)(2)C6H3]V(OC6F5)(2) [P(CH3)(3)](2)（11）符合这一途径。计算表明，化合物10和11在金属环丁烷的β -氢化物消除和丙烯的还原消除后，通过双分子途径形成，丙烯本身被证明是exergonic的，对金属环丁烷的形成具有较低的热力学障碍。1-己烯与一系列不同立体电子位的钒烷基烷（n -2,6- x2c6h3）（OC6Y5）[P-(CH3)(3)](2) V[CHSi(CH3)(3)] [X = CH3, Y = Cl(1)]的自分解反应的相对转化X = CH(CH3)(2), Y = Cl (6), X = CH(CH3)(2), Y = F(7)]。研究发现，更多的给电子配体减少了转化，表明-氢化物消除比双分子分解更有利。有机反应产物的分析表明，丙烯的还原消除发生在乙烯插入新形成的钒氢键之前。
Vanadium alkylidenes can be highly active initiators for ring-opening metathesis polymerization of cyclic olefins; however, attempts to expand their use to cross metathesis have been unsuccessful due to catalyst decomposition. Detailed knowledge of the decomposition reaction is imperative to guide future catalyst design. Herein, we demonstrate that beta-hydride elimination is the dominant decomposition pathway during cross metathesis. The isolated vanadium decomposition products [N-2,6-(CH3)(2)C6H3-](OC6Cl3)[P(CH3)(3)](2)VCl (10) and [N-2,6-(CH3)(2)C6H3]V(OC6F5)(2) [P(CH3)(3)](2) (11), generated from two separate catalysts, agree with this pathway. Compounds 10 and 11 were shown computationally to form via bimolecular routes after beta-hydride elimination from the metallocyclobutane and reductive elimination of propylene, which was itself demonstrated to be exergonic with low thermodynamic barriers to metallocyclobutane formation. Relative conversions in the selfmetathesis of 1-hexene with the series of vanadium alkylidenes of various sterics and electronics (N-2,6-X2C6H3)(OC6Y5)[P-(CH3)(3)](2) V[CHSi(CH3)(3)] [X = CH3, Y = Cl (1); X = CH(CH3)(2), Y = Cl (6), X = CH(CH3)(2), Y = F (7)] were determined. It was found that builder, yet more electron-donating ligands decreased conversions, indicating that beta-hydride elimination is favored over bimolecular decomposition. Analysis of organic reaction products demonstrated that reductive elimination of propylene occurs before insertion of ethylene into the newly formed vanadium-hydrogen bond.