多酸基手性功能材料的制备及不对称串联催化烯烃制备环状碳酸酯的研究

Recently, the selective and efficient conversion of light olefins with CO2 as a C1 building block into value-added enantiomerically pure cyclic carbonates has attracted great interest from chemists and governments due to its tremendous potential economic and environmental impact, especially considering the increasing worldwide greenhouse effect. Because light olefins are the most inexpensive and readily available chemical building blocks, a one-pot procedure that processes an olefin through a chain of discrete catalytic steps with multiple transformations using a single workup stage is highly desirable for the environmentally benign conversion of carbon dioxide to fine chemicals. Inspired by natural enzymatic processes, chemists have attempted to emulate natural reaction cascades by developing auto-tandem catalytic reactions in which a substrate is catalytically transferred through two or more mechanistically distinct reactions without the addition of reactants or catalysts and without altering the reaction conditions. Chiral MOFs are ideally suited for heterogeneous asymmetrically catalytic conversions, since they can be tailored by judicious combinations of the building blocks for specific applications. An ongoing challenge for the development of auto-tandem catalytic processes has been beyond the selection and incorporation of two or more catalytic sites by modifying these moieties in the building block of the original MOFs, but includes the achievement of compatibility between the reaction intermediates and synergy of the multiple catalytic cycles. Here by incorporating a pyrrolidine moiety as a chiral organocatalyst and a polyoxometalate as an oxidation catalyst, a powerful approach is devised to achieve a tandem catalyst for the efficient conversion of CO2 into value-added enantiomerically pure cyclic carbonates. The multi-catalytic sites are orderly distribution and spatial matching in the framework. The captured CO2 molecules are synergistically fixed and activated by well positioned pyrrolidine and amine groups, providing further compatibility with the W=Ot activated epoxidation intermediate and driving the tandem catalytic proceeded in a single workup stage and an asymmetric fashion. The structural simplicity of the building blocks and the use of inexpensive and readily available chemical reagents render this approach highly promising for the development of practical homochiral materials for CO2 conversion.

手性环状碳酸酯是医药、功能材料的重要前驱体和中间体。本项目从合成化学中CO2催化活化这一具有挑战性科学问题和前沿研究入手，设计发展新型多功能催化体系，发展具有高效、原子经济性和绿色化的串联反应合成策略，实现从化学工业原料烯烃出发与CO2一步高效构建手性环状碳酸酯的目标。将具有氧化催化功能的多酸、功能桥联配体及手性基团引入到金属有机框架中，构建多功能手性POMOFs反应平台，实现结构的可控组装和定向制备；考察POMOFs的空间尺寸、催化位点空间布局对催化效果的影响，调控催化位点和底物之间立体、电子匹配，以期发挥POMOFs内部孔道的特殊空间限制，实现不对称串联催化反应动力学控制和立体选择性控制；运用现代分析手段和动力学方法，深入研究催化反应过程，探究其催化机理，为实现高效、高选择性制备手性环状碳酸酯的实际应用拓展新的研究思路，为我国精细化工、功能材料等方面的发展提供科学基础。

本项目以发展高效、高立体选择性的手性多酸基金属–有机框架（POMOF）催化剂为核心目标，利用多酸和有机分子的功能特性，设计合成具有不同结构和催化功能的POMOFs。发展了具有高效性、原子经济性和绿色化等特点的串联反应合成策略，实现手性POMOFs在不对称串联催化反应过程中立体选择性和动力学控制。此外，发展了光催化烯烃及胺的氧化，不对称羟醛缩合和氧化反应的串联反应。主要研究内容如下：.1）将具有良好氧化催化功能的多酸基团如Keggin型[BW12O40]5–、金属取代型 [Zn(H2O)(PW11O39)]6−及同多酸[W10O32]4–，桥连配体4，4-联吡啶(BPY)、氨基-4，4-联吡啶(NH2-BPY)、萘酰亚胺(DPNDI)等，不对称催化功能的吡咯基团（PYI）和金属中心构建了5类具有不同结构类型的手性POMOFs，分别是：Co-DPNDI-PYI（1），Zn-DPNDI-PYI（2），ZnW−PYI（3），CuPYIs（4）NH2-Co-PYIs（5）。对合成的POMOFs进行了详尽的结构和性质表征。考察不同结构POMOFs的空间尺寸、催化活性位点布局、孔道限阈作用、催化剂对底物分子的作用模式等因素对手性诱导的影响。.2）根据所得催化剂结构和性质不同，开展了一系列催化反应，考察反应时间、溶剂及氧化剂等对反应的影响，优化最佳反应条件；通过核磁和液相色谱等手段考察产率和选择性，评价催化剂的效率和对映选择性；运用物理化学手段和现代波谱分析方法如红外、紫外、荧光光谱、电化学、核磁和液相等现代分析手段以及动力学方法，研究催化反应机理。具体如下：化合物1利用连续光诱导电子转移过程结合氢转移(HAT)和单电子转移(SET)过程催化卤代烃还原及具有类碳酸氢酶结构的Co位点和PYI的N-甲基咪唑可以有效活化CO2，实现在没有辅助催化剂（如TBAB或DMAP）和温和条件下高效催化环氧化物和CO2耦合；化合物2和3实现了O2为氧化剂烯烃的氧化和胺的氧化耦合反应；化合物4实现了由小分子醛和酮经羟醛缩合环氧化串联反应直接制备手性环氧酮；化合物5作为双官能团催化剂高效催化Aldol/Knoevenagel缩合反应。.目前共发表SCI学术论文10篇，其中一区2篇；2区5篇（top 3篇），成果发表在J. Catal.、ACS Appl. Mater. Interfaces 等上。