氢化酶活性位[Fe-S]簇合物的模拟修饰及其质子耦合电子转移反应研究

Hydrogen is one of the optimal energy due to its high energy density and being friendly to the environment after combustion. The driving force to mimic the catalytic reaction of hydrogenase enzymes for the interconversion of H2 with protons is the requirement for efficient and inexpensive catalyst in hydrogen fuel cell. In this project, organic phosphine containing aromatic amine is used to modify/mimic the active site of [Fe-S] clusters in hydrogenase，and to explore the proton-coupling electron transfer reaction of the active clusters as well as the catalytic reaction for the reduction of protons and the reverse reaction with oxidation of H2. The protonated amido group within the chelating ring formed by metal coordination with the desigend chelate ligand, is favourable thermodynamically for the proton transfer due to its close enough proximity of the active site in [Fe-S] cluster. Furthermore, the configuration of chelating ring is also adjusted with the rigid of aromatic amine.The acceptable ability of amido N to proton would be tuned by changing the electron density of aromatic amine to impose on the proton-electron transfer. By adjusting the steric, electronic and solvent effect in model complex of [Fe-S] based on the change of the substituent group on the designed ligands, as well as by the cooperative coordination of P and pyridyl N atom in ligand, the catalytic activity of [Fe-S] clusters could be optimized, while the proton-coupling electron transfer reaction will be researched by NMR tracking reacton, electrochemical cyclic voltammetry and the isotopic exchange between H and D. Based on these experiment results, the suitable mechanics of proton-coupling electron transfer reaction can be deduced, and the parameters of thermodynamics and kinetics can be calculated. The target of this project is to pursue the theoretical basis for developing high efficient and practical hydrogen electrocatalyst.

氢由于能量密度高及燃烧对环境友好是最理想的能源之一。模拟氢化酶对氢的可逆催化反应在于发展高效便宜的氢燃料电池催化剂，实现氢能广泛应用。本项目拟用含芳香胺有机膦配体对氢化酶活性位[Fe-S]簇合物进行修饰模拟探索簇合物活性中心的质子耦合电子转移反应及其对氢可逆催化反应。所设计配体螯合配位后螯合环上质子化的胺基由于接近金属活性位在热力学上有利于质子转移反应，同时芳香胺的刚性影响螯合环的构型。通过芳香基团电子密度的改变调控胺基N对质子的接受能力从而影响质子电子转移。通过膦上取代基的改变、同一配体中膦和吡啶氮协同配位探索[Fe-S]簇合物中心的空间效应、电子效应和溶剂效应等优化簇合物中心的催化活性。利用循环伏安法、NMR反应跟踪以及氢和氘同位素交换等手段研究质子耦合电子转移反应，推导反应机理，计算质子耦合电子转移反应的动力学和热力参数，为发展高效实用氢催化剂提供理论依据。

氢由于能量密度高及燃烧对环境友好是最理想的能源之一。模拟氢化酶对氢的可逆催化反应在于发展高效便宜的氢燃料电池催化剂，实现氢能广泛应用。人们通过对氢化酶活性中心[2Fe-2S]的模拟修饰，探索模型物的质子电子转移反应历程，理解氢化酶对氢的可逆催化反应机理，筛选出优良的催化剂。目前人们主要在氢化酶模型物[2Fe-2S]的N或者C桥头进行修饰以及改变供电子基团的配体配位修饰达到研究目的。本项目组通过四年的努力，用含芳香胺有机膦为配体合成了20个含氢化酶活性中心[2Fe-2S]簇的模拟物，并通过IR，NMR以及晶体结构等对这些模型物进行了较好的表征，通过循环伏安法探索了这些模型物的电化学行为以及它们在质子酸条件下的电催化产氢行为。通过在模型物中引入不同的含N基团试图探索模型物的电催化质子电子转移历程的影响因素。研究发现模型物中含N基团相对于[Fe-Fe]间的碱性强弱对质子电子转移历程起着重要的作用，而与模型物是否含桥头N还是桥头C关系不大，吡啶基和二茂铁基胺的碱性大于有机脂肪胺；含N基团的质子化是动力学优先的过程，而[Fe-Fe]间桥连氢形成是一个热力学稳定的过渡态，且含N基团的质子化有利于模型物的电催化产氢行为。研究发现含二茂铁胺基双膦配合物13和具有刚性结构的配合物20（见正文）相对稳定且电催化效果也相对较好。另外也合成了8个金属有机框架结构配合物，研究了它们相应的电催化行为和化学催化行为：基于酰腙的三个Ni配合物中只有含醋酸根（Ac-）螯合的配合物稳定性较好，且具有较好的电催化质子产氢能力；基于氮甲基的三角架型的三羧酸配体构筑的二维和三维Ni配合物在KOH溶液中具有一定的电催化析氧能力，同时也研究了两个Cu12八面体笼状和一个In12四面体笼状化合物催化二氧化碳成环碳酸酯和催化醛或酮合成α-氨基腈的Strecker反应，发现这些笼状配合物作为路易斯酸催化剂对底物都具有空间选择性。四面体型的In12笼状化合物稳定性较好，既能催化活化二氧化碳合成环碳酸酯、也能催化醛或酮进行Strecker反应。