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随着全球“温室效应”和能源危机的加剧,近几年二氧化碳作为一种丰富、无毒、廉价的碳一原料广受关注.目前,在温和条件下实现二氧化碳的化学转化仍然是一个十分具有挑战性的课题,其关键的科学问题是二氧化碳分子的有效活化.本文发现,在不添加任何助催化剂的条件下,季膦盐型双功能金属Salen配合物不仅能够以有机胺、含氢硅烷和二氧化碳为原料,在温和条件下通过甲酰化反应实现系列甲酰胺类衍生物的高效合成,而且能够催化二氧化碳和环氧化合物的环加成反应,从而实现环状碳酸酯的宏量制备.催化实验及动力学研究结果表明,该双功能催化剂通过金属活性中心和卤素阴离子之间的分子内协同催化作用,既可利用高活性锌氢键调控含氢硅烷中的硅氢键,又能通过高活性铝氧键激活环氧化物的三元环,进而导致二氧化碳的方便插入及高效活化.譬如:当使用1.0 mol%锌催化剂时,仅加入1倍当量的苯硅烷,在25℃和0.5 MPa的条件下,反应6 h后N-甲酰苯胺收率高达99%;而当使用0.5 mol%铝催化剂时,在100℃和2.0 MPa的条件下反应2 h,环加成反应转化率接近100%,环状碳酸酯选择性可达99%.另外,上述两个反应都表现出优异的底物扩展性,具有良好的官能团相容性.在此基础上通过构建反应动力学模型,采用在线红外跟踪技术,阐明了协同活化机制在二氧化碳催化转化过程中的作用原理及共性/个性规律,丰富并发展了二氧化碳活化的基本理论.最后,单组分催化剂可通过溶剂调变的方式很容易实现回收及再利用,表现出“均相催化,两相分离”的特点.循环使用五次后催化活性和选择性未见明显下降.
In recent years, as a rich, nontoxic and inexpensive carbon-carbon feedstock, carbon dioxide has drawn much attention as global warming and the energy crisis intensify. At present, the chemical conversion of carbon dioxide under mild conditions is still a Is a very challenging topic, the key scientific issue is the effective activation of carbon dioxide molecules.In this paper, we found that without adding any promoter, quaternary phosphonium bifunctional metal Salen complexes can not only organic amine, hydrogen Silane and carbon dioxide as raw materials, the formation of a series of formamide derivatives under mild conditions by formylation reaction, and can catalyze the cycloaddition reaction of carbon dioxide and epoxy compounds to achieve macroscopic preparation of cyclic carbonates The results of catalytic experiments and kinetics show that the bifunctional catalyst can utilize the high activity zinc-hydrogen bond to control the hydrogen-hydrogen bond in the hydrosilane through the intramolecular synergistic catalysis between the metal active center and the halogen anion, Activation of the three-membered ring of epoxides by a highly reactive aluminum-oxygen bond leads to the convenient insertion and efficient activation of carbon dioxide. 1.0 mol% zinc catalyst, only 1 equivalent of benzene silane was added, and the yield of N-formanil was as high as 99% after reacting for 6 h at 25 ℃ and 0.5 MPa. When 0.5 mol% aluminum catalyst was used, , At 100 ℃ and 2.0 MPa for 2 h, the conversion of the cycloaddition reaction was close to 100%, and the cyclic carbonate selectivity was up to 99% .In addition, both of the above two reactions showed excellent substrate scalability , And has good functional group compatibility.Based on this, the reaction kinetics model was established and the on-line infrared tracking technology was used to elucidate the action principle and commonality / character of the synergistic activation mechanism in the process of carbon dioxide catalytic conversion, enriching and developing The basic theory of carbon dioxide activation Finally, the single-component catalyst can be easily recovered and reused through solvent modulation, showing the characteristics of “homogeneous catalysis, two-phase separation.” After five cycles of recycle, the catalytic activity And no significant decline in selectivity.