四齿N2P2配体螯合的镍配合物设计合成及电催化制氢性能研究

【作者】 刘燕；

【导师】 张范军；

【作者基本信息】 曲阜师范大学 ， 有机化学， 2025， 硕士

【摘要】 氢气作为一种清洁高效的可再生能源,其完全燃烧产物只有水,实现了零碳排放,是化石燃料的理想替代品之一。以电化学方式制备氢气可实现能源的可持续利用。因此,开发新型的基于地球丰产金属的产氢催化剂引起了化学家广泛的研究兴趣。受自然界氢化酶活性中心结构和功能的启发,设计合成新型氢化酶活性中心模拟物是当前产氢分子电催化剂的研究热点。基于此,本论文模拟[Ni-Fe]氢化酶活性位点的催化功能,设计合成了一类单核镍配合物。在结构表征的基础上,以弱酸醋酸为质子源,构建了有机溶剂中不含贵金属的均相电催化产氢体系。本论文合成了一类含有N、P原子的四齿螯合配体RN2P2(R=H、PivNH、NH2),以及配体稳定的金属镍、铁配合物([RN2P2Ni(Ⅱ)]2+、[RN2P2Fe(Ⅱ)]2+)。通过核磁共振波谱(NMR)、X射线单晶衍射、红外光谱(IR)、高分辨质谱(HRMS-ESI)等技术对配体及金属配合物的结构进行了表征。该螯合配体能够维持金属配合物的稳定性,并且金属中心还具有空的配位点,有利于催化产氢过程中氢化物中间体M-H形成。利用金属配合物中乙腈分子易离去的特点,通过引入负氢的方法合成了金属铁氢配合物,并借助1HNMR对金属Fe-H配合物的结构进行了表征;使用相同的方法合成了金属镍氢化物,并通过X射线单晶衍射对镍氢化物的结构进行了表征研究。利用循环伏安法(Cyclic Voltammetry)测试了 Ni(Ⅱ)配合物的电化学性质,发现该类镍配合物具有电催化质子还原制氢的潜在活性。以弱酸醋酸(HOAc)作为质子源,在有机溶剂中构筑了基于非贵金属-镍的均相电催化制氢体系。向有机配体结构中引入酰胺或氨基,能够通过取代基的电子效应和空间位阻效应提高配合物的稳定性以及催化活性。循环伏安测试结果表明,配合物[N2P2Ni(NCMe)2]2+、[PivNHN2P2Ni(NCMe)]2+、[NH2N2P2Ni(NCMe)2]2+在 100 mM HOAc浓度下催化质子还原产生氢气的催化转化频率(tumoverfrequency,TOF)分别为:170 s—1、252 s-1、469 s-1,表明合成的Ni(Ⅱ)配合物可作为分子电催化剂代替贵金属来催化质子还原产氢。在反应机理探究过程中,对催化过程可能涉及的几种中间体配合物(Ni0、NiⅠ、NiⅡ-H)进行了合成、分离与表征。其中,镍氢配合物[2-H]+能够直接与酸反应释放出H2,表明Ni(Ⅱ)-H物种可能为催化产氢过程中的关键中间体。研究发现,配体PivNHN2P2结构中酰胺基团N-H能够与Ni-H形成分子内氢键,在提高镍氢化物稳定性的同时降低了催化反应的过电势,进而提高了催化剂的电催化产氢性能。根据电化学测试和计算结果,我们推测此类金属镍配合物催化制氢的可能机理为EECC或ECEC途径。更多还原

【Abstract】 Hydrogen is a clean and efficient renewable energy source,as well as an ideal alternative to fossil fuels,because its combustion product is only water and achieving zero-carbon emissions.Using electrochemical treatment to product hydrogen achieved sustainable utilization of energy.Therefore,developing new catalysts for hydrogen production based on earth-abundant metals has aroused chemists’ extensive research interest.Inspired by the structure and function of hydrogenase activity center in nature,the design and synthesis of new hydrogenase activity center simulators is the research focus of hydrogen-producing molecular electrocatalysts.Based on this,a kind of mononuclear nickel complexes was designed and developed by simulating the catalytic function of the active site of[Ni-Fe]hydrogenase.On the basis of structural characterization,a homogeneous electrocatalytic hydrogen production system without non-noble metals in organic solvents was constructed with weak acid acetic acid as proton source.In this work,we synthesized a series of tetradentate tripodal RN2P2(R=H,PivNH,NH2)ligands containing N,P atom,and nickel or iron complexes([RN2P2Ni(II)]2+,[RN2P2Fe(II)]2+)with corresponding ligands.The structural informations of ligands and complexes were analyzed via Nuclear Magnetic Resonance(NMR),X-ray crystallography,Infrared Radiation(IR),High Resolution Mass Spectrum(HRMS-ESI)and other testing approaches.The chelating ligand can maintain the stability of metal complexes,and the metal center also has empty coordination sites,which is beneficial to the formation of hydride intermediate M-H in the process of catalytic hydrogen production.Based on the characteristic that acetonitrile molecules in metal complexes are easy to leave,metal iron-hydrogen complexes were synthesized by introducing negative hydrogen,and the structure of Fe-H complexes was characterized by 1H NMR.Metal nickel-hydrogen complexes were synthesized by the same synthesis method,and the structure of Ni-H complexes were characterized by X-ray single crystal diffraction.The electrochemical characters of Ni(II)complexes were tested through cyclic voltammetry,and finding the potential activity of nickel complexes in electrocatalytic proton reduction for H2 production.Using weak acid acetic acid as proton source,a homogeneous electrocatalytic hydrogen production system based on non-noble metalnickel was constructed in organic solvent.The introduction of amide groups into the structure of organic ligands can improve the stability and catalytic activity of the complexes by electronic and steric effects.The cyclic voltammetry test results indicate that the turnover frequency(TOF)of the[N2P2Ni(NCMe)2]2+,[PivNHN2P2Ni(NCMe)]2+,[NH2N2P2Ni(NCMe)2]2+complexes are 170 s-1,252 s-1,469 s-1,respectively.The research shows that the synthesized Ni(II)complex can be used as molecular electrocatalyst to replace precious metals in catalyzing proton reduction to produce hydrogen.In the study of reaction mechanism,the possible intermediates(Ni0,NiⅠ,NiⅡ-H)during the catalytic process were synthesized,separated and characterized.Among them,nickel hydride complexe[2-H]+can directly react with acid to release H2,which can be used as a key intermediate in the process of catalytic hydrogen production.The results show that the N-H of amide group in the structure of ligand PivNHN2P2 can form intramolecular hydrogen bonds with Ni-H,which improves the stability of nickel hydride and reduces the overpotential of catalytic reaction,thus improving the electrocatalytic hydrogen production performance of the catalyst.According to the electrochemical tests and calculation results,we speculate that the possible catalytic mechanism of such nickel complexes is EECC or ECEC route.更多还原