一类受生物启发的双膦双硒镍配合物的合成及其电催化产氢性能

Synthesis of Six Bio-Inspired Nickel-Based Complexes Ligated with Diselenolate Derivatives and Diphosphine Ligands,and Application to Electrocatalytic H_(2) Evolution

自然界中,[NiFeSe]氢化酶比[NiFe]氢化酶具有更高的催化产氢活性和特殊的耐氧性。其较高的催化活性机制被认为跟[NiFeSe]氢化酶上所取代的硒(Se)原子密切相关。因此,[NiFeSe]氢化酶的特殊结构、性质及催化机制强烈激发科学家们设计并合成各种模拟[NiFeSe]氢化酶活性中心的镍铁硒或镍硒配合物(也即受生物启发的模拟物)。本论文工作首先合成及结构表征了六个基于双硒配体与含二茂铁的双膦配体的镍硒配合物(2a–2c,3a–3b,4);然后将这些镍硒配合物用作[NiFeSe]氢化酶的功能模型物,利用电化学方法,以三氟乙酸为质子给体测定了相应的电催化产氢活性。在相同实验条件下,分别研究了双硒配体上不同的取代基团,及含二茂铁的双膦配体上不同取代基等结构修饰方式对镍硒配合物催化产氢性能的影响。结果表明:这些镍硒配合物的催化产氢活性跟双硒配体及双膦配体的结构有很大关系,对应的催化转化频率(TOF)分别为12182 s^(−1)(2a),15385 s^(−1)(2b),20359 s^(−1)(2c),106 s^(−1)(3a),794 s^(−1)(3b),13580 s^(−1)(4)。其中,1,2-二硒-4,5-二甲基和1,1’-双(二苯膦)二茂铁配体与镍离子配位形成的镍硒配合物2c具有最好的电催化活性(TOF=20359 s^(−1)),其产氢性能已大大超过先前我们课题组所报道的由1,2-苯二硒、1,1’-双(二苯膦)二茂铁所配位形成的镍硒配合物1(TOF=7838 s^(−1))。

In recent years,there has been an intense effort to develop renewable alternatives to fossil fuels for meeting the ever-increasing global energy need.Molecular dihydrogen(H2)is the ideal energy carrier for the 21st century because it has high energy density and its combustion releases only water,and electrocatalysis is a powerful tool for its wide use.Developing new H2-evolving molecular electrocatalysts with cheap and earth-abundant elements is highly desirable.Among all kinds of H2-generating catalysts,[NiFe]-hydrogenases(H2ases)have the active site featuring a redox-active{Ni(cysteinate)4}center bridged through two of its cysteine residues to a redox-inactive{Fe(CN2)(CO)}moiety.As a class of known natural enzymes,[NiFe]-H2ases are promising candidates because they have inexpensive nickel and/or iron atoms at the active sites and can catalyze the reversible reduction of H+to H2 with high efficiency comparable to the noble-metal platinum.However,the catalytic behaviors of most artificial H2ases-like active sites are usually inhibited by the existence of a small amount of O2,which strongly limit their practical application.As such,it is attractive to develop new analogues of enzyme active sites to address this issue.On the other hand,[NiFeSe]-H2ases,which are obtained by the introduction of Se into[NiFe]-H2ases,have exceptional properties conducive for H2 production,such as high H2 generation performance,marginal inhibition by H2,and high tolerance to O2.The mechanistic understanding of[NiFeSe]-H2ases function guides the design and synthesis of Se-substituted Ni-based molecular catalysts,and selection of suitable bio-inspired catalysts enables applications in catalysis for hydrogen evolution reaction(HER).In this contribution,six bio-inspired neutral nickel-based complexes(2a–2c,3a–3b,4)with diselenolate derivatives and diphosphine ligands have been prepared and structurally characterized.These complexes are important in the function of[NiFeSe]-hydrogenase models toward their application as electrocatalysts for the HER.The substituent effects of diselenolate and diphosphine ligands on the catalytic activities of hydrogen production by these nickel(II)complexes are studied experimentally.When using a glassy carbon electrode,all the complexes are efficient electrocatalysts for H2 production with different turnover frequencies(TOFs)of 12182 s^(−1)(2a),15385 s^(−1)(2b),20359 s^(−1)(2c),106 s^(−1)(3a),794 s^(−1)(3b),13580 s^(−1)(4).The present results indicate that the nickel(II)complex 2c ligated by a 4,5-dimethyl-1,2-benzenediselenolate and 1,1’-bis(diphenylphosphino)ferrocene ligand,shows the highest efficiency,which surpasses the activity of a previously dppf-supported nickel(II)1,2-benzenediselenolate with a TOF of 7838 s^(−1).We believe that our results will encourage the development of the design of highly efficient Ni-based selenolate molecular catalysts.