Understanding and Expanding Zinc Cation/Amine Frustrated Lewis Pair Catalyzed C-H Borylation.
Understanding and Expanding Zinc Cation/Amine Frustrated Lewis Pair Catalyzed C-H Borylation.
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DOI：
10.1021/acscatal.2c05995
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发表时间：
2023-02-17
期刊：
影响因子：
12.9
通讯作者：
Ingleson, Michael J.
中科院分区：
文献类型：
--
作者：
Grundy, Matthew E.;Sotorrios, Lia;Bisai, Milan Kumar;Yuan, Kang;Macgregor, Stuart A.;Ingleson, Michael J.
[（NacNac）Zn（DMT）][B（C6F5）4]，1，（NacNac ={（2，6-iPr2H3C6）N（CH3）C} 2CH），DMT = N，N-二甲基-4-甲苯胺），由（NacNac）ZnEt或（NacNac）ZnH出发，通过两条路线合成。配合物1是使用邻苯二酚硼烷（CatBH）进行（杂）芳烃的C-H硼基化反应的有效（预）催化剂，其中H2是唯一的副产物。范围包括弱活化底物，如2-溴噻吩和苯并噻吩。计算研究阐明了一个合理的反应机制，具有22.4千卡/摩尔（N-甲基吲哚硼基化）的总自由能跨度，与实验观察一致。从1开始的计算机理通过用CatBH置换DMT以形成[（NacNac）Zn（CatBH）]+，D进行，其中CatBH经由氧与锌结合，这使得硼中心基于CatB-基LUMO的能量更加亲电。D和DMT的组合充当受抑刘易斯对（FLP），以通过被DMT去质子化的芳烃阳离子在逐步过程中实现C-H硼基化。随后的B-H/[H-DMT]+脱氢偶联和CatBH从CatBAr的锌配位层的置换关闭循环。计算还揭示了一种可能的催化剂分解途径，涉及氢化物从硼转移到锌形成（NacNac）ZnH，其与CatBH反应最终形成Zn（0）。此外，关键的限速过渡态都涉及的碱，因此微调的空间和电子参数的碱使进一步轻微的增强C-H硼化活性的系统。概述该FLP介导过程的所有步骤的机制将促进用于C-H硼基化和其他转化的其他主族FLP催化剂的开发。
[(NacNac)Zn(DMT)][B(C6F5)4], 1, (NacNac = {(2,6-iPr2H3C6)N(CH3)C}2CH), DMT = N,N-dimethyl-4-toluidine), was synthesized via two routes starting from either (NacNac)ZnEt or (NacNac)ZnH. Complex 1 is an effective (pre)catalyst for the C–H borylation of (hetero)arenes using catecholborane (CatBH) with H2 the only byproduct. The scope included weakly activated substrates such as 2-bromothiophene and benzothiophene. Computational studies elucidated a plausible reaction mechanism that has an overall free energy span of 22.4 kcal/mol (for N-methylindole borylation), consistent with experimental observations. The calculated mechanism starting from 1 proceeds via the displacement of DMT by CatBH to form [(NacNac)Zn(CatBH)]+, D, in which CatBH binds via an oxygen to zinc which makes the boron center much more electrophilic based on the energy of the CatB-based LUMO. Combinations of D and DMT act as a frustrated Lewis pair (FLP) to effect C–H borylation in a stepwise process via an arenium cation that is deprotonated by DMT. Subsequent B–H/[H-DMT]+ dehydrocoupling and displacement from the coordination sphere of zinc of CatBAr by CatBH closes the cycle. The calculations also revealed a possible catalyst decomposition pathway involving hydride transfer from boron to zinc to form (NacNac)ZnH which reacts with CatBH to ultimately form Zn(0). In addition, the key rate-limiting transition states all involve the base, thus fine-tuning of the steric and electronic parameters of the base enabled a further minor enhancement in the C–H borylation activity of the system. Outlining the mechanism for all steps of this FLP-mediated process will facilitate the development of other main group FLP catalysts for C–H borylation and other transformations.
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影响因子：
8.4
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