【作者】 赵联明；

【导师】 郭文跃； 王勇；

【作者基本信息】 中国石油大学 ， 化工材料， 2009， 博士

【摘要】 过渡金属催化氧原子转移反应在石油化工、生物过程以及环境化学中具有特别重要的意义。目前催化剂的设计和改进逐渐由纯技艺型向分子设计水平方向转变。但是,催化剂分子设计需要建立在对催化机理有着全面深入认识的基础上。但是由于溶剂效应等外在因素的干扰,人们很难认清反应的活性中心以及中间体的内禀特性等。气相实验结合理论计算可以排除常规实验中诸多干扰因素,揭示催化反应的内禀属性,为催化剂的开发和设计提供理论指导。本文以过渡金属离子Mn⁺、Fe⁺、Co⁺和Ni⁺催化N₂O与CO、烷烃（C₂H₆）、炔烃（C₂H₂）和芳香烃（C₆H₆）的氧原子转移反应为研究对象,采用量子化学方法,系统研究过渡金属离子催化氧原子转移反应的内禀机理,确定控制氧原子转移催化效率的本质因素。理论计算结果表明:在金属离子中介的CO还原N₂O反应中,Co⁺和Ni⁺首先通过N-O插入机理与N₂O反应脱掉氮气生成氧化物MO+,随后氧化物被CO还原并通过O-C耦合机理再生金属离子并释放CO₂。自旋禁忌和较高的能垒阻碍了NiO⁺的生成,CoO⁺的形成因自旋反转而效率低下。因此Co+和Ni+对CO还原N₂O反应不具备催化特性。当有第二个N₂O与Co⁺配位时,Co⁺/2N₂O/CO反应势能面由于官能团效应而大幅降低,促进反应进行。Fe⁺催化N₂O氧化乙炔始于Fe⁺（6D和4F）分别通过直接的氧提取和N-O插入机理与N₂O反应生成FeO⁺。在第二步催化循环中,乙炔与新生成的FeO+结合后可经直接H提取机理得到产物乙炔醇;也可以经过环化形成c-CHCHOFe⁺后,伴随有直接离解（脱甲酰基甲烯）、C-C插入（脱乙烯酮）、C-to-O氢转移（脱乙炔醇）和/或C-to-C氢转移（脱乙烯酮和CO）四条可能的反应通道,其中最有利的反应路径是沿环化至C-to-C氢转移的脱乙烯酮和CO通道。脱CO伴随产物FeCH₂+被另一分子N₂O还原过程组成了催化循环的第三步。该过程经历初始的直接氧提取生成OFeCH2+后,发生分子内重排形成甲醛加合物Fe+-OCH2。考虑到从初始反应获得的能量,此反应在能量上也是非常有利的。在Fe+和Co+参与的N₂O氧化乙烷反应中,首先Fe+和Co+还原N₂O得到相应的金属氧化物离子。第二步,乙烷与新生成的氧化物结合后,可经直接H提取和/或逐步H转移生成羟基中间体（HO）M+（CH2CH3） （M = Fe和Co）。最后羟中间体经β-H转移通道发生脱水和脱乙烯反应,或通过C-O耦合通道生成乙醇并使金属离再生子。脱水伴随产物MC₂H4+也可以进一步被N₂O氧化。氧化首先通过N-O激发脱掉氮气生成OMC₂H4+,随后体系可经直接H提取机理生成乙烯醇并再生M+,此外Fe+体系还生成FeC₂H2+和FeOH+两种副产物。OMC₂H4+也可以经环化生成c-CH2CH2OM+,随后发生C-to-O氢转移（脱乙烯醇）、C-O耦合（脱环氧乙烷）、C-to-C氢转移（脱乙醛）和/或α-H提取（脱乙醛）反应,其中Fe+还可以通过C-C插入机理脱甲醛以及通过C-to-C氢转移和/或α-H提取机理脱甲烷。脱乙烯伴随产物MOH2+进一步与N₂O反应逐步脱掉氮气和水分子生成活性MO +。对N₂O氧化乙烷反应,Fe+具有良好的催化活性,但是由于产物复杂并伴随大量副产物,其选择性较差。Co+参与的反应主要产物为乙醛和乙醇,具有较好的选择性,但是受生成CoO+的速率过低的影响在室温下不具备催化活性。Mn⁺、Co⁺和Ni⁺催化N₂O氧化苯气相反应包含MO⁺和M⁺（C6H₆）中介的两种催化循环。在M⁺（C₆H₆）中介的催化循环中,Mn+和Co⁺初始形成M⁺（C6H₆）后,N₂O与之配位并被金属离子激发形成（C₆H₆）M⁺O（N₂）。热的（C₆H₆）M⁺O（N₂）释放掉一分子氮后可经非自由基和/或氧-插入两种机理生成苯酚并再生催化剂M⁺。M⁺与苯结合时获得的巨大能量不仅提供了N-O激发的驱动力,而且促使苯的氧化可以沿单一势能面（Mn+的七重态和Co+的三重态势能面）以单态反应方式进行。在MO+中介的反应循环中,由于第一步形成金属氧化物过程中受高反应能垒和/或自旋反转限制,阻碍了Mn⁺、Co⁺和Ni⁺以MO⁺中介的方式对苯的N₂O氧化进行有效催化。更多还原

【Abstract】 The oxygen-atom transport catalyzed by transition metal ions is of paramount importance in chemical engineering, biology, and environmental process. Now, it is more and more popular in designing and improving catalysts at a molecular level, which is based on the extensively understanding of the catalytic reaction mechanisms. In“real-life situation”, however, the solvents and other disturbing factors obscure the intrinsic features of a reaction center or the reactive intermediates. Gas-phase experiments combining with theoretical calculations are particularly well-suited for the elucidation of basic properties of isolated molecules and probing the elementary reactions because they are not hampered by various disturbing factors. In this thesis, the reaction of N₂O with CO, alkane （C₂H₆）, alkine （C₂H2）, and arene （C6H₆） catalyzed by Mn+, Fe⁺, Co⁺, and Ni+ is chosen as a model for studying the catalysis of oxygen-atom transport by quantum chemistry calculations. The intrinsic mechanisms of these reactions are systematically investigated and the rate-determining steps are elucidated. The calculated results are as follows.In the gas-phase Co⁺ and Ni+-mediated N₂O reduction by CO, firstly, metal ions reaction with N₂O forms N₂ and MO+ via the N-O insertion mechanism. Then, the nascent oxide reduction by CO could account for the M+-regenerated product, CO₂, through the C-O coupling mechanism. The NiO+ formation is inhibited by both the high energy barrier and the spin inversion. On the other hand, spin inversion also slows down the reaction rate in CoO+ formation process. Thus, both metal ions are unable to work as a catalyst in N₂O reduction by CO. Coordination of second N₂O by Co⁺ has a positive effect, leading the catalytic reaction could proceed along a thermodynamically and kinetically highly favorable path.The Fe⁺-catalyzed oxidation of acetylene by N₂O starts with Fe⁺（6D and 4F） reaction with N₂O yielding FeO+ through direct O-abstraction and N-O insertion mechanisms, respectively. For the second leg of catalytic cycles, after the coordination of acetylene by nascent FeO+, the reaction could yield ethynol via direct H abstraction mechanism. Alternatively, the system also converts into a“metallaoxacyclobutene”structure, followed by four possible pathways, i.e., direct dissociation （for producing formylcarbene）, C-C insertion （for products ketene）, C-to-O hydrogen shift （for ethynol）, and/or C-to-C hydrogen shift （for ketene and CO）. The most favorable channel is oxidation to ketene and carbon monoxide along the cyclization - C-to-C hydrogen shift pathway. Reduction of the CO loss partner FeCH2+ by another N₂O molecule constitutes the third step of the catalytic cycle, which involves a direct abstraction of O-atom from N₂O giving OFeCH2+ and then an intramolecular rearrangement to form formaldehyde adduct Fe⁺-OCH2. Considering the energy acquired from the initial reactants, this reaction is also energetically favored.In the gas-phase Fe⁺ and Co⁺-mediated oxidation of ethane by N₂O, Fe⁺ and Co⁺ reduction N₂O gives rise to metal oxide ion firstly. For second step of the catalytic cycle, after the coordination of ethane by nascent oxide, the direct and/or stepwise （metal ion mediated） H shift could carry the system into hydroxyl intermediate （HO）M+（CH2CH3）, which could account for H2O and C₂H4 loss products viaβ-H shift channel and ethanol elimination product through C-O coupling pathway. The H2O loss partner MC₂H4+ could react with another N₂O molecule. N₂O coordinates to MC₂H4+ and gets activated by metal ion to yield （C₂H4）M+O（N₂） through a N-O insertion mechanism. The thermal （C₂H4）M+O（N₂） would release a nitrogen molecule and then is further oxidized through two different mechanisms, i.e., direct H abstraction and/or cyclization. The former mechanism accounts for the ethenol formation. Additionally, for Fe⁺, the reaction also could form the byproducts of FeC₂H2+ and FeOH+. The other mechanism involves a c-CH2CH2OM+ structure, followed by four possible pathways, i.e., C-to-O hydrogen shift （for producing ethenol）, C-O coupling （for products oxirane）, C-to-C hydrogen shift （for acetaldehyde）, and/orα-H abstraction （for acetaldehyde）. Additionally, for Fe⁺, the reaction also could form formaldehyde via C-C insertion pathway and methane throughα-H abstraction channel. The C₂H4 loss partner MOH2+ also could react with N₂O generating active MO+ after stepwise loss of N₂ and H2O. Fe⁺ could catalyze the reaction of ethane with N₂O, but its selectivity is very poor because yielding a lot of byproducts. For Co⁺, the mainly products are acetaldehyde and ethanol, indicating a good selectivity. However, Co⁺ is unable to work as a catalyst due to the poor efficiency of the CoO+ formation at room temperature.The Mn+, Co⁺, and Ni+-catalyzed oxidation of benzene by N₂O may involve two different catalytic cycles, i.e., mediated by M+（benzene） and MO+, respectively. In the M+（benzene）-mediated catalytic cycle, for both Mn+ and Co⁺, after the initial formation of M+（benzene）, the oxidant N₂O coordinates to the nascent complex and gets activated by metal ion to yield （C6H₆）M+O（N₂） through a N-O insertion mechanism. The thermal （C6H₆）M+O（N₂） would release a nitrogen molecule and then is further oxidized to phenol regenerating the active catalyst M+ through two different mechanisms, i.e., nonradical and/or O-insertion. The large energy acquired from the benzene association not only provide the driving force for the N-O activation as well as the whole oxidation reaction but also make it possible for the benzene oxidation to proceed on a same potential energy surface （PES, septet for Mn+ and triplet for Co⁺） under the single-state reactivity （SSR） paradigm. For the alternative MO+-mediated oxidation mechanism, spin inversion as well as high energy barrier in the course of the N-O activation imply that both Mn+, Co⁺, and Ni+ are unable to work as a catalyst.更多还原