Methylrhenium trioxide revisited: mechanisms for nonredox oxygen insertion in an M-CH3 bond.
Methylrhenium trioxide revisited: mechanisms for nonredox oxygen insertion in an M-CH3 bond.
复制标题
重温三氧化甲基铼：M-CH3 键中非氧化还原氧插入的机制。
DOI：
10.1021/ja0714742
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发表时间：
2007
影响因子：
15
通讯作者：
Jonas Oxgaard
中科院分区：
文献类型：
--
作者：
Jason M. Gonzales;R. Distasio;R. Periana;W. Goddard;Jonas Oxgaard
三氧化甲基铼 (MTO) 具有在室温下与外部氧化剂 (H2O2) 在碱性条件下按化学计量生成甲醇的罕见能力。为了使用这种转化作为非氧化还原氧化 C-O 偶联的模型，使用密度泛函理论 (DFT) 阐明了其机制。我们的研究显示了形成甲醇的几种可能的反应途径，最低净势垒 (DeltaH++) 为 23.3 kcal mol-1。速率决定步骤是直接“Baeyer-Villiger”型协同氧插入到 MTO 中，形成三氧化甲氧基铼。低能过渡态的关键是电子密度的提供，首先，从HOO(-)到-CH3基团（使-CH3更亲核，HOO-更亲电），其次，从Re-C键同时形成Re-O键和断裂O-O键（从而在Re-C键断裂时形成Re-O键）。反过来，MTO 进行这些转移的能力可以追溯到金属中心的亲电子性质以及缺乏可接近的 d 轨道。如果存在可接近的 d 轨道，它们很可能会提供所需的电子密度而不是 M-CH3 部分，因此该键不会被破坏。具有类似质量的其他金属中心，例如 PtIV 或 IrV，可能能够产生相同类型的化学反应。
Methylrhenium trioxide (MTO) has the rare ability to stoichiometrically generate methanol at room temperature with an external oxidant (H2O2) under basic conditions. In order to use this transformation as a model for nonredox oxidative C-O coupling, the mechanisms have been elucidated using density functional theory (DFT). Our studies show several possible reaction pathways to form methanol, with the lowest net barrier (DeltaH++) being 23.3 kcal mol-1. The rate-determining step is a direct "Baeyer-Villiger" type concerted oxygen insertion into MTO, forming methoxyrhenium trioxide. The key to the low-energy transition state is the donation of electron density, first, from HOO(-) to the -CH3 group (making -CH3 more nucleophilic and HOO- more electrophilic) and, second, from the Re-C bond to both the forming Re-O and breaking O-O bonds, simultaneously (thus forming the Re-O bond as the Re-C bond is broken). In turn, the ability of MTO to undergo these transfers can be traced to the electrophilic nature of the metal center and to the absence of accessible d-orbitals. If accessible d-orbitals are present, they would most likely donate the required electron density instead of the M-CH3 moiety, and this bond would thus not be broken. It is possible that other metal centers with similar qualities, such as PtIV or IrV, could be competent for the same type of chemistry.