Isomerization of epoxides into versatile allylic alcohols is an atom-economical synthetic method to afford vicinal bifunctional groups. Comprehensive density functional theory (DFT) calculations were carried out to elucidate the complex mechanism of a bimetallic Ti/Co-catalyzed selective isomerization of epoxides to allyl alcohols by examining several possible pathways. Our results suggest a possible mechanism involving (1) radical-type epoxide ring opening catalyzed by Cp₂Ti(III)Cl leading to a Ti(IV)-bound β-alkyl radical, (2) hydrogen-atom transfer (HAT) catalyzed by the Co(II) catalyst to form the Ti(IV)-enolate and Co(III)–H intermediate, (3) protonation to give the alcohols, and (4) proton abstraction to form the Co(I) species followed by electron transfer to regenerate the active Co(II) and Ti(III) species. Moreover, bimetallic catalysis and two-state reactivity enable the key rate-determining HAT step. Furthermore, a subtle balance between dispersion-driven bimetallic processes and entropy-driven monometallic processes determines the most favorable pathway, among which the monometallic process is energetically more favorable in all steps except the vital hydrogen-atom transfer step. Our study should provide an in-depth mechanistic understanding of bimetallic catalysis.

中文翻译：

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双金属 Ti/Co 协同催化环氧化物异构化为烯丙醇的双态反应

将环氧化物异构化为多功能烯丙醇是一种原子经济的合成方法，可提供邻位双官能团。通过检查几种可能的途径，进行了综合密度泛函理论（DFT）计算，以阐明双金属 Ti/Co 催化环氧化物选择性异构化为烯丙醇的复杂机制。我们的结果提出了一种可能的机制，涉及（1）Cp ₂ Ti(III)Cl催化的自由基型环氧化物开环，产生 Ti(IV) 结合的 β-烷基，(2) 氢原子转移 (HAT) 催化通过 Co(II) 催化剂形成 Ti(IV)-烯醇化物和 Co(III)-H 中间体，(3) 质子化得到醇，(4) 质子夺取形成 Co(I) 物质，然后电子转移以再生活性 Co(II) 和 Ti(III) 物质。此外，双金属催化和双态反应性实现了决定速率的关键 HAT 步骤。此外，色散驱动的双金属过程和熵驱动的单金属过程之间的微妙平衡决定了最有利的途径，其中单金属过程在除了重要的氢原子转移步骤之外的所有步骤中都更加有利。我们的研究应该提供对双金属催化的深入机理理解。