Elucidating metal hydride reactivity using late transition metal boryl and borane hydrides: 2c-2e terminal hydride, 3c-2e bridging hydride, and 3c-4e bridging hydride
Elucidating metal hydride reactivity using late transition metal boryl and borane hydrides: 2c-2e terminal hydride, 3c-2e bridging hydride, and 3c-4e bridging hydride
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使用后过渡金属硼基和硼烷氢化物阐明金属氢化物反应性：2c-2e 末端氢化物、3c-2e 桥接氢化物和 3c-4e 桥接氢化物
DOI：
10.1039/c8cy00766g
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发表时间：
2018
影响因子：
5
通讯作者：
Ke Zhuofeng
中科院分区：
文献类型：
--
作者：
Li Yinwu;Liu Jiahao;Hou Cheng;Shao Youxiang;Qu Ling-Bo;Zhao Cunyuan;Ke Zhuofeng
金属催化剂在可持续能源、环境、石化工业和许多重要的化学过程中发挥着重要的催化作用。尽管如此，金属氢化物反应性背后的谜团仍然存在。以刘易斯酸-过渡金属（LA TM）氢化物配合物促进的烯烃氢化反应为模型反应，采用密度泛函理论（DFT）研究了不同类型的末端取代基和桥连取代基的反应活性差异.选择PBP（μ-H）CoH和DPB（μ-H）NiH配合物分别作为硼基型和硼烷型LA-TM氢化物的代表模型。在硼烷型配合物DPB（μ-H）NiH中，桥氢化物的反应活性低于端氢化物.然而，与之形成鲜明对比的是，在硼基型配合物PBP（μ-H）CoH中，桥接氢化物比末端氢化物更具有反应性。展开的电子结构的典型特征，合理化的反应性差异的起源。在sp3硼烷型DPB（μ-H）NiH配合物中，桥氢化物形成典型的三中心双电子（3c-2 e）B-H-Ni键。在sp2硼基PBP（μ-H）CoH配合物中，桥氢化物形成了一个不寻常的三中心四电子（3c-4 e）B-H-Co键。3c-2 e桥接氢化物通过两个LA位点稳定，导致比正常2c-2 e末端氢化物更低的亲核性。同时，3c-4 e桥氢化物显示出更强的自由氢化物特征，导致比2c-2 e末端氢化物更高的亲核性。提出了氢化物亲核的一般趋势：3c-4 e桥氢化物> 2c-2 e末端氢化物> 3c-2 e桥氢化物。金属氢化物反应性的这些基本方面应该有助于机械理解和涉及金属氢化物络合物的催化剂/材料设计。
Metal hydrides play important roles in catalysis for sustainable energy, the environment, the petrochemical industry, and many important chemical processes. Despite this significance, the mystery behind metal hydride reactivity still remains. This theoretical study reveals a surprising reactivity discrepancy for different types of terminal hydrides and bridging hydrides, with Lewis acid–transition metal (LA–TM) hydride complex promoted alkene hydrogenations as model reactions, using density functional theory (DFT) studies. PBP(μ-H)CoH and DPB(μ-H)NiH complexes were chosen as representative models for the boryl type and the borane type LA–TM hydride, respectively. The bridging hydride is less reactive than the terminal hydride in the borane type complex DPB(μ-H)NiH. However, in sharp contrast, the bridging hydride is more reactive than the terminal hydride in the boryl type complex PBP(μ-H)CoH. Typical features of the electronic structure are unfolded to rationalize the origin of the reactivity discrepancy. The bridging hydride in the sp3 borane type DPB(μ-H)NiH complex forms a typical three-center two-electron (3c–2e) B–H–Ni bond. In the sp2 boryl PBP(μ-H)CoH complex, the bridging hydride forms an unusual three-center four-electron (3c–4e) B–H–Co bond. The 3c–2e bridging hydride is stabilized by two LA sites, leading to a lower nucleophilicity than that of a normal 2c–2e terminal hydride. Meanwhile the 3c–4e bridging hydride shows a stronger free-hydride character, resulting in a higher nucleophilicity than that of a 2c–2e terminal hydride. A general hydride nucleophilic trend is proposed: 3c–4e bridging hydride > 2c–2e terminal hydride > 3c–2e bridging hydride. These fundamental aspects of metal hydride reactivity should be helpful for mechanistic understanding and catalyst/material design involving metal hydride complexes.