新型刚性非对称钳形金属配合物的开发及在催化氢转移中的应用

Transition metal-catalyzed hydrogen transfer reactions are attracting more and more interests in the process chemistry of biomass conversion, petrochemicals, fine chemicals and material chemicals. Although the achievements have been made in the past decades, there are still some issues to be resolved. First, the catalyst loading cannot satisfy the acquirement of industry due to the potentially inherent instability of the catalyst. Second, the catalyst need to be well decorated and/or designed toward improving the selectivity of the hydrogen transfer reactions. Moreover, development of Fe, Ni and Co-catalyzed hydrogen transfer reactions is of great value, however, their mechanisms are still not clear enough. New strategies need to be established. The key to resolve these issues is developing new ligands. In this project, we will import a ring-fused framework to pincer ligand. The pincer ligand involving the rigid cycle with carbene or cyclometallic coordination is believed to be able to improve the stability of the catalyst. The coordination angel can be finely tuned by changing the cycle and thus play an important role in regulating the coordination environment, which could benefit for controlling the selectivity. Furthermore, the pincer ligand with pyridine imine and the rigid framework is redox active, which can provide a good chance for developing a new Fe, Co and Ni-catalyzed catalytic system. Besides, the stability of the rigid pincer metal complex will facilitate the mechanism investigations. Overall, developing new rigid pincer metal complexes will improve the efficiency and selectivity of hydrogen transfer reactions and deserves to study.

过渡金属催化的氢转移在生物质转化、石油化工、精细化工及材料开发等领域受到关注。但是仍然有许多问题亟待解决。首先，催化剂用量较大，远达不到工业化规模生产的需求，需要提高催化剂稳定性；其次，氢转移反应的选择性控制需要催化剂骨架具备很好的调控性；再次，Fe，Co，Ni等催化的氢转移反应有很大的发展空间，机理仍然比较模糊，新的活化方式需要探索。解决这些问题的关键在于发展新型配体。本项目拟引入刚性环烷基骨架到钳形配体中，结合卡宾或环金属骨架，将有效提高催化剂的稳定性；改变环烷基大小可以有效调控配位角，从而改变金属的配位环境，将有利于调控反应选择性；此外，氧化还原特性的吡啶-亚胺骨架与刚性骨架结合，将对Fe，Co，Ni的催化模式产生影响。另外，稳定的刚性钳形金属配合物有利于展开机理研究，揭示反应规律。总的来说，新型刚性钳形金属配合物的开发将有利于提高氢转移的效率和选择性，值得研究。

氢转移过程广泛存在于生物质转化、石油化工、精细化工以及储氢材料的开发等领域。近年来，过渡金属催化的氢转移反应也得到迅速发展，极大地拓展了成键方式和反应类型，为化合物的合成和结构的衍生化提供了更多的选择。但是，氢转移反应也存在着催化剂效率有待提高，反应选择性控制较难以及反应机理模糊等问题。针对这些问题，本项目基于刚性的四氢喹啉骨架，围绕着新型刚性配体的开发、金属配合物制备及其氢转移反应应用开展相关的研究工作，一方面优化了配体骨架的合成工艺，成功的开发了系列新型的配体库，包括NN,NO等双齿配体,NNN,CNN，NNP等三齿钳形配体，并制备表征了相关的Pd，Co，Ni等配合物，另一方面将这些新型的配合物成功应用于以醇为氢源的Pd催化的炔基或烯基氢芳化反应、Co催化的炔基硅氢化反应、Ni催化的氢转移C-烷基化、N-烷基化反应；Co催化的以硅烷为氢源的单炔及二炔的选择性硅氢化反应、酰胺还原反应等。开发的新型催化剂表现了高稳定性，比如Co催化炔基马氏硅氢化反应，TON可以达到4950；同时，由于配体灵活的位点调控性，催化剂也高选择性的实现了炔或者烯的氢转移还原转化，以及在短链醇的活化转化上也有了一些突破，为后续工作的开展奠定了基础。另外，基于各种氢转移反应为模型，同步进行了反应机理研究，重点利用反应动力学和配合物实验，研究关键活性物种，揭示了金属氢物种的生成及转化规律。