Stannyl Cations for the Hydrogenation of Carbon Dioxide to Methanol and Methyl Formate

本提案的主要目标是开发新型的基于锡基阳离子的刘易斯对催化剂[R3Sn(dot)L]+ （L = 2电子氧供体），该催化剂能够在降低二氧化碳的同时快速激活H2，选择性地形成商品化学品甲醇（CH3OH）或甲酸甲酯（HCO2CH3），其温度和压力低于目前用于工业规模生产的温度和压力。这些基于主基团的体系对H2的激活是基于“受挫刘易斯对”（FLP）化学的扩展，尽管使用的催化剂更类似于“经典”的给受体加合物。这项研究建立在我们非常有希望的初步结果的基础上，这些结果证明了Bu3SnH/催化[Bu3Sn]+体系在温和条件下将CO2快速氢锡化成甲氧基（ch30 -）和氧化物（O2-）等量物，以及游离的HCO2CH3。令人兴奋的是，这种混合物与氢（H2）反应释放出CH3OH， H2O和HCO2CH3，并再生Bu3SnH还原剂。这表明，所有阶段的催化方案的二氧化碳加氢可以实现，虽然氢解目前太慢。这项工作概述的方法是通过增加垂链烷基的大小来合理地修饰锡基阳离子，从而增加路易斯对加合物中的“挫折”量。这有望显著改善H2活化和随后的CO2还原步骤的动力学。在本工作方案的过程中，自然会开发出以廉价和丰富的锡化合物为基础的新型（耐水）加氢催化剂，这些催化剂无疑将用于其他工业相关的转化（例如有机羰基加氢制醇）。实现主要目标的具体关键目标是：1。合成含有大量R基团的新前驱体（R3SnH, R3SnX; R =烷基，X = NTf2, OTf）。研究了锡基阳离子路易斯对加合物[R3Sn(dot)L]+ (L = R3SnOCH3, R3SnOSnR3)活化H2的能力，并将观察到的速率与结构联系起来。3 .对CO2和拟反应中间体的氢锡化反应进行详细的机理研究。研究Sn-O键氢解的机理，建立有利于生成CH3OH或HCO2CH3.5的相关实验参数（如温度、压力）。整合从目标1-4中获得的速率数据、机制信息和实验变量，以优化CO2选择性催化加氢成CH3OH和/或HCO2CH3的最佳[R3Sn]+物质。

The principal goal of this proposal is to develop novel stannyl cation-based Lewis pair catalysts [R3Sn(dot)L]+ (L = 2electron oxygen donor) which are capable of rapidly activating H2 with concomitant reduction of CO2, to selectively form the commodity chemicals methanol (CH3OH) or methyl formate (HCO2CH3), at lower temperatures and pressures than currently used for their industrial-scale production. The activation of H2 by these main-group based systems is based on an extension of 'frustrated Lewis pair' (FLP) chemistry, albeit using catalysts that more closely resemble 'classical' donoracceptor adducts. This research builds upon our extremely promising preliminary results which demonstrate the competence of a Bu3SnH/catalytic [Bu3Sn]+ system for the rapid hydrostannylation of CO2 under mild conditions to methoxide (CH3O-) and oxide (O2-) equivalents, in addition to free HCO2CH3. Excitingly, reaction of this mixture with hydrogen (H2) liberates CH3OH, H2O and HCO2CH3, and regenerates the Bu3SnH reductant. This demonstrates that all stages of a catalytic protocol for CO2 hydrogenation can be achieved, although hydrogenolysis is at present too slow. The approach outlined in this work is to rationally modify the stannyl cation by increasing the size of the pendant alkyl groups and hence increase the amount of 'frustration' in the Lewis pair adducts. This is expected to markedly improve the kinetics of both H2 activation and subsequent CO2 reduction steps. Fundamentally new (water-tolerant) hydrogenation catalysts based on inexpensive and abundant Sn compounds will naturally develop during the course of this work programme, which will undoubtedly find use in other industrially relevant transformations (e.g. organic carbonyl hydrogenation to alcohols).The specific key objectives to achieve the main aim are:1. Synthesise new precursors (R3SnH, R3SnX; R = alkyl, X = NTf2, OTf) incorporating bulky R groups.2. Investigate stannyl cation Lewis pair adducts, [R3Sn(dot)L]+ (L = R3SnOCH3, R3SnOSnR3), for their ability to activate H2, and correlate observed rates with structure.3. Conduct detailed mechanistic studies on the hydrostannylation of both CO2 and proposed reaction intermediates.4. Investigate the mechanism of Sn-O bond hydrogenolysis, and establish the relevant experimental parameters (e.g. temperature, pressure) which favour the production of either CH3OH or HCO2CH3.5. Consolidation of rate data, mechanistic information, and experimental variables obtained from objectives 1-4 in order to optimise the best [R3Sn]+ species for selective catalytic hydrogenation of CO2 to CH3OH and/or HCO2CH3.