Selective Reduction of CO2 to CH4 by Tandem Hydrosilylation with Mixed Al/B Catalysts
Selective Reduction of CO2 to CH4 by Tandem Hydrosilylation with Mixed Al/B Catalysts
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DOI：
10.1021/jacs.6b01497
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发表时间：
2016-04-27
影响因子：
15
通讯作者：
Chen, Eugene Y-X.
中科院分区：
文献类型：
--
作者：
Chen, Jiawei;Falivene, Laura;Chen, Eugene Y-X.
该贡献报道了通过串联氢化硅烷化用混合主族有机路易斯酸（LA）催化剂[Al（C6 F5）（3）+ B（C6 F5）（3）] {[Al] + [B]}将CO高度选择性还原成CH 4的第一个实例。如通过该全面的实验和计算研究所示，在该独特的串联催化过程中，[Al]有效地介导了整个还原循环的第一步，即通过LA介导的C=O活化将CO2固定为HCOOSiEt 3（1），而[B]不能促进相同的转化。另一方面，[B]显示为用于随后的还原步骤2-4的优异催化剂，即通过受抑的刘易斯对（FLP）型Si-H活化，更碱性的中间体[1至H2 C（OSiEt 3）（2）（2）至H3COSiEt 3（3）并最终至CH 4]的氢化硅烷化。因此，通过[Al]和[B]的所需组合，已经开发了一种高度选择性的氢化硅烷化还原CO 2系统，实现了高达94%的高CH 4产率。[Al]和[B]之间显著不同的催化行为归因于[Al]的更高的总体刘易斯酸性，其源自两个冲突因素（电子和空间效应），这使得[Al]更倾向于与CO2以及随后的中间体1、2和3形成稳定的[Al]-底物（中间体）加合物。总的来说，[Al]和[B]在CO2的总还原中的作用不仅是互补的，而且是协同的，这使得[Al]介导的第一还原步骤和[B]介导的后续步骤都具有催化作用。
This contribution reports the first example of highly selective reduction of CO, into CH4 via tandem hydrosilylation with mixed main-group organo-Lewis acid (LA) catalysts [Al(C6F5)(3) + B(C6F5)(3)] {[Al] + [B]}. As shown by this comprehensive experimental and computational study, in this unique tandem catalytic process, [Al] effectively mediates the first step of the overall reduction cycle, namely the fixation of CO2 into HCOOSiEt3 (1) via the LA-mediated C=O activation, while [B] is incapable of promoting the same transformation. On the other hand, [B] is shown to be an excellent catalyst for the subsequent reduction steps 2-4, namely the hydrosilylation of the more basic intermediates [1 to H2C(OSiEt3)(2) (2) to H3COSiEt3 (3) and finally to CH4] through the frustrated Lewis pair (FLP)-type Si-H activation. Hence, with the required combination of [Al] and [B], a highly selective hydrosilylative reduction of CO, system has been developed, achieving high CH4 production yield up to 94%. The remarkably different catalytic behaviors between [Al] and [B] are attributed to the higher overall Lewis acidity of [Al] derived from two conflicting factors (electronic and steric effects), which renders the higher tendency of [Al] to form stable [Al]-substrate (intermediate) adducts with CO2 as well as subsequent intermediates 1, 2, and 3. Overall, the roles of [Al] and [B] are not only complementary but also synergistic in the total reduction of CO2, which render both [Al]-mediated first reduction step and [B]-mediated subsequent steps catalytic.