双金属卟啉协同催化氧气选择性氧化环烷烃合成醇、酮研究

At present, the selectivities are very poor and the reaction depth can not be controlled facilely in oxidation of cycloalkanes with dioxygen catalyzed by metalloporphyrins, thus the oxidation products can not be synthesized precisely. In order to solve these problems, metalloporphyrins with two metal centers are designed through covalent bonds in this project based on the results of pre-research, in which the cycloalkanes will be converted to oxidation intermediates cycloalkyl hydrogen peroxides catalyzed by Co、Mn、Fe and so on, and the cycloalkyl hydrogen peroxides will be transformed to cycloalkyl alcohols or cycloalkyl ketones selectively catalyzed by Cu、Zn、Cr and so on. As a result, the selectivities in the catalytic oxidation of cycloalkanes will be increased obviously due to the synergetic function of the two metal centers. And then the synergistic function mechanism of the two metal centers will be explored employing quantum chemical calculation and reaction kinetics study, based on which the strategy to adjust the formation of products in catalytic oxidation of cycloalkanes will be established. At last, the precise synthesis of the oxidation products will be realized through the construction of catalytic system with high selectivities. The idea has not been documented by far to realize the precise synthesis of the products in the catalytic oxidation of cycloalkanes through construction of metalloporphyrins with two metal centers. This project will not only has important theoretical value in the catalytic oxidation of C-H and C-C bonds in the cycloalkanes precisely, but also has important applied value in the synthesis of cycloalkyl alcohols and ketones from cycloalkanes through a green process, which are important fine chemical intermediates and products. The achievements in this study will also enrich and develop the theory in the biomimetic oxidation of cycloalkanes catalyzed by metalloporphyrins.

针对金属卟啉催化O2氧化环烷烃过程中存在的氧化产物选择性差、氧化深度难以控制、目标产物无法精准合成的问题，结合前期预研结果，本项目旨在通过共价键构筑双金属中心卟啉，以Co、Mn、Fe等金属中心催化氧化环烷烃生成中间产物环烷基过氧化氢，以Cu、Zn、Cr等催化转化中间产物选择性生成环烷醇或酮，通过双金属中心协同作用提高产物的选择性。借助量子化学计算、反应动力学等手段取得双金属中心卟啉催化O2氧化环烷烃的协同机制，提炼出环烷烃催化氧化的调控策略，以此构筑高选择性催化体系，实现氧化产物精准合成。其中，双金属中心卟啉协同催化氧化环烷烃，实现氧化产物精准合成的研究思路，目前未见文献报道。本项目不仅对环烷烃C-H键和C-C键精准催化氧化具有重要的理论研究价值，而且对环烷烃绿色催化氧化制备环烷醇、酮等精细化工中间体和产品也具有重要的应用研究价值。成果有助于丰富和发展金属卟啉催化氧化环烷烃的仿生催化理论。

针对分子氧催化氧化环烷烃C-H键存在的部分氧化产物易深度氧化，选择性低等问题，基于金属卟啉构筑双金属中心催化体系，以Co(II), Mn(II), Fe(II)为第一催化中心，催化O2氧化环烷烃生成氧化中间产物环烷基过氧化物；以Cu(II), Zn(II), Ni(II)为第二催化中心，催化转化环烷基过氧化物，防止其无序热分解转化，减少体系中的自由基，防止部分氧化产物深度氧化，提高其选择性。研究发现，第二金属不仅可以催化转化环烷基过氧化氢，降低其无序热分解，还可以强化环烷基过氧化物的氧化性，催化氧化C-H键，实现转化率的进一步提升。本项目开展过程，性能优异且有代表性的双金属催化体系分别有四(4-氯苯基)卟啉钴(II)(T(4-Cl)PPCo(II))&四(4-氯苯基)卟啉锌(II)(T(4-Cl)PPZn(II))二元催化体系，T(2-Cl)PPCo(II)&T(4-Cl)PPCu(II)，T(4-COOCH3)PPCo(II)&Zn(OAc)2，T2-NaPBr8Co(II)&Zn(OAc)2，3D MOF PCN-222(Co)&Zn(OAc)2，2D MOF Co-TCPPCu双金属催化体系，3D MOF PCN-224(Co&Cu)，3D MOF PCN-224(Co&Ni)，均相双金属卟啉催化体系(Tris(4-Cl)PPCo(II))&C6&(4-Cl)PPZn(II))等。以环己烷催化氧化为模型反应，底物转化率和部分氧化产物(醇，酮和过氧化物)的总选择性分别达到了4.29%和99%，4.41%和97%，6.53%和96%，6.21%和95%，5.51%和94%，5.31%和95%，5.72%和88%，7.26%和85%，4.41%和97%，均优于相应均相金属卟啉的催化性能。上述催化体系，均具有良好的底物普适性，有效防止了O2催化氧化C-H键过程中底物转化率提高造成的部分氧化产物选择性降低，实现了底物转化率和产物选择性的同时提高。研究还发现，具有限域性反应空间的催化体系，如PCN-224(Co&Ni)，可有效降低反应过程自由基的无序扩散，实现部分氧化产物选择性的进一步提高。本项目对双金属中心协同催化氧化C-H键的机制也进行了系统研究，为烃类C-H键的高效，选择性氧化官能团化提供了一个比较新颖的反应模型，对理论研究和工业应用均具有一定的参考价值。