【作者】 王静；

【导师】 杨大伟； 韩继斌；

【作者基本信息】 大连理工大学 ， 化学工程， 2025， 硕士

【摘要】 氮氧化物（N_xO_y）之间的复杂转化过程构成了生物化学地球氮循环,其中,反硝化过程和羟胺氧化还原过程作为关键环节,在维持氮循环平衡中发挥着重要作用。近年来,仿生化学家们根据反硝化和羟胺氧化还原过程所涉及的金属酶的活性中心结构特征,设计合成了各式各样的结构与功能模型配合物,旨在揭示N_xO_y配位活化与转化的一般性规律。然而,受N_xO_y转化过程复杂性的限制,理性设计并精准构筑理想的功能模型配合物,进而从分子层面认识反硝化与羟胺氧化还原过程仍然充满挑战性。基于此,本论文采用大位阻金刚烷基硫桥联双钴配合物为仿生功能模型,系统探究NO₃^-和NH₂OH在双钴中心活化转化的新模式,为从分子水平认识氮循环的反硝化和羟胺氧化还原过程提供重要的实验数据。本小节以金刚烷基硫桥联双钴配合物[Cp*Co（μ-SAd）（μ-Br）CoCp*]（1）作为反应前体,通过双钴协同实现了对反硝化过程中NO₃^-逐步还原为NO的功能模拟:首先,配合物1与KOH发生复分解反应生成双钴羟桥配合物[Cp*Co（μ-SAd）（μ-OH）CoCp*]（4）,其能够在单电子氧化条件下与Na NO₃反应转化为双钴硝酸盐桥联配合物[Cp*Co（μ-SAd）（μ-η¹:η¹-NO₃）（μ-OH）CoCp*][PF₆]（3[PF₆]）;随后,配合物3[PF₆]在2e^-/2H⁺条件下,经历连续的质子耦合电子转移（PCET）过程转化为双钴亚硝酸盐桥联配合物[Cp*Co（μ-SAd）（μ-η¹:η¹-NO₂）（μ-OH）CoCp*][PF₆]（2[PF₆]）;进一步在4e^-/3H⁺条件下,转化为双钴NO桥联配合物[Cp*Co（μ-SAd）（μ-NO）CoCp*]（5）。该反应体系有助于从分子层面揭示在反硝化过程中多金属协同介导NO₃^-→NO₂^-→NO多电子还原转化的本质规律。同时,配合物1还能够实现对氮循环氨氧化过程的关键中间体NH₂OH的配位活化与转化为NO或NH₃的功能模拟:当配合物1与等当量NH₂OH反应时,反应体系通过双钴协同实现了N-O键断裂,同时捕获氨基和羟基,生成[Cp*Co（μ-SAd）（μ-NH₂）（μ-OH）CoCp*][BPh₄]（7[BPh₄]）。在2e^-/H⁺存在下,配合物7[BPh₄]经历PCET过程脱羟基转化为双钴氨化物[Cp*Co（μ-SAd）（μ-NH₂）CoCp*]（10）,进一步酸化释放NH₃,实现了NH₂OH→NH₃的仿生还原功能模拟。当配合物7[BPh₄]进一步与NH₂OH反应时,则脱羟基生成NH₂O^-以μ-η¹:η¹形式配位于双钴中心的羟胺基桥联配合物[Cp*Co（μ-SAd）（μ-η¹:η¹-NH₂O）（μ-NH₂）CoCp*][BPh₄]（8[BPh₄]）,其可以被O₂氧化,生成双钴NO桥联配合物[Cp*Co（μ-SAd）（μ-NO）（μ-NH₂）CoCp*][BPh₄]（9[BPh₄]）,实现了NH₂OH→NO的仿生氧化功能模拟。该双钴体系为进一步开发拓展基于羟胺氧化还原酶功能导向的仿生催化体系提供了新契机。更多还原

【Abstract】 The biogeochemical nitrogen cycle is composed of complicated transformations among nitrogen oxides,in which denitrification and redox processes of hydroxylamine serve as key segments,playing critical roles in maintaining the balance of nitrogen cycle.In recent years,bioinorganic chemists have designed and synthesized diverse structural and functional model complexes inspired by the structural characteristics of the active centers of metalloenzymes involving in the denitrification and hydroxylamine redox processes,aiming to reveal general principles for the coordination activation and transformation of nitrogen oxides.However,due to the limitation of N_xO_y conversion pathways’complexity,rational design and precise construction of ideal functional models to mechanistically elucidate denitrification and hydroxylamine redox processes at the molecular level remain challenging.Hence,in this dissertation,a bulky admantyl thiolate-bridged dicobalt complex is employed as a bioinspired functional model to systematically investigate novel pattern for activation and conversion of NO₃^-and NH₂OH at the dicobalt center,providing critical experimental data for understanding mechanisms of denitrification and hydroxylamine redox transformations in the nitrogen cycle from the molecular level.Using the admantyl thiolate-bridged dicobalt complex[Cp*Co（μ-SAd）（μ-Br）CoCp*]（1）as a precursor,functional mimicking for the stepwise reduction of NO₃^-to NO during the denitrification process was achieved through the cooperative effect between the dicobalt centers:First,complex 1 undergoes metathesis with KOH to generate a hydroxide-bridged dicobalt complex[Cp*Co（μ-SAd）（μ-OH）CoCp*]（4）,which can react with Na NO₃ to generate a dicobalt nitrate-bridged complex[Cp*Co（μ-SAd）（μ-η¹:η¹-NO₃）（μ-OH）CoCp*][PF₆]（3[PF₆]）under one-electron oxidation condition.Subsequently,3[PF₆]went through successive proton-coupled electron transfer processes to convert into dicobalt nitrite-bridged complex[Cp*Co（μ-SAd）（μ-η¹:η¹-NO₂）（μ-OH）CoCp*][PF₆]（2[PF₆]）in the presence of 2e^-/2H⁺.Furthermore,complex 2[PF₆]can transform into dicobalt nitrosyl-bridged complex[Cp*Co（μ-SAd）（μ-NO）CoCp*]（5）in the presence of 4e^-/3H⁺.This reaction system is very helpful to elucidate the essence of the multi-electron reduction process（NO₃^-→NO₃^-→NO）involving in denitrification mediated by the cooperation of multiple metal centers at the molecular level.Simultaneously,complex 1 can also realize the functional mimicking for the coordination activation of hydroxylamine and its conversion into nitric oxide or ammonia,which serves as a key intermediate during the ammonia oxidation process in the nitrogen cycle.When complex 1reacted with one equivalent of NH₂OH,the N–O bond cleavage was achieved through the cooperative interaction of the two cobalt centers.The dicobalt scaffold can simultaneously trap NH₂^-and OH^-groups to generate[Cp*Co（μ-SAd）（μ-NH₂）（μ-OH）CoCp*][BPh₄]（7[BPh₄]）.In the presence of 2e^-/H⁺,complex 7[BPh₄]underwent PCET processes and the removal of hydroxide to generate dicobalt amide complex[Cp*Co（μ-SAd）（μ-NH₂）CoCp*]（10）,which can release NH₃ upon acidification.This reaction system achieve the bioinspired functional mimicking of the reduction process（NH₂OH→NH₃）.When complex 7[BPh₄]further reacted with NH₂OH,the removal of the hydroxide took place to afford dicobalt hydroxylamino-bridged complex[Cp*Co（μ-SAd）（μ-η¹:η¹-NH₂O）（μ-NH₂）CoCp*][BPh₄]（8[BPh₄]）featuring a NH₂O^-group in aμ-η¹:η¹ coordination pattern.Upon exposure to O₂,complex 8[BPh₄]can be oxidized to generate dicobalt nitrosyl-bridged complex[Cp*Co（μ-SAd）（μ-NO）（μ-NH₂）CoCp*][BPh₄]（9[BPh₄]）,which simulates the biomimetic oxidative process of NH₂OH→NO.This dicobalt system provides new opportunities for developing bioinspired catalytic systems aiming to the function of the hydroxylamine oxidoreductase.更多还原