【作者】 王磊；

【导师】 王新平；

【作者基本信息】 南京大学 ， 无机化学， 2018， 博士

【摘要】 双自由基作为自由基化学的一个重要分支,由于具有多样的光、电、磁特性,在有机化学、物理化学、分子电子学、有机自旋电子学等领域已经成为研究热点。大多数自由基非常活泼,寿命短,易发生氧化、聚合、夺氢等反应,稍晚于三苯甲基自由基发现的席勒烃和齐齐巴宾烃就是两例经典的例子。如何稳定和分离双自由基成为研究的关键,除了碳原子外,硼原子和氮原子也可以作为双自由基优良的自旋承载中心。本论文总结了含硼及双(三芳胺)自由基化合物的研究现状,分离和表征了一系列新型的含硼和含氮自由基化合物,并结合理论计算对其结构与性质进行了研究。本论文的主要工作列举如下:一、利用弱配位阴离子稳定并分离了两例四芳基联蒽二胺双阳离子化合物,即12+··和22+··,从结构、光谱、磁性和理论计算等方面对它们进行了研究。结果表明,端基苯环对位取代基的变化对四芳基联蒽二胺双阳离子化合物的结构、双自由基性质的影响十分微弱。联蒽结构单元对双自由基性质起了主要作用。蒽环基团之间近乎正交的结构使得两个单自由基之间轨道共轭程度减小,化合物12+··和22+··均表现出很高的双自由基性质。此外,化合物12+··和22+··基态均为开壳层单线态,但是具有十分小的单线态和三线态能量差,可以视为单线态和三线态简并的双自由基。二、我们利用空间位阻效应稳定和分离了席勒烃和齐齐巴宾烃的含硼类似物32-和42-,并通过相关实验表征手段及理论计算对其结构和性质进行了研究。单晶结构表征、SQUID测试和DFT计算表明32-和42-均为闭壳层化合物,且不能热激发为开壳层;此外我们还分离得到了一例硼阴离子单自由基3·-,通过对其EPR谱图的模拟和DFT计算表明3·-的自旋密度是平均分布在两个硼原子上的硼单自由基。三、我们合成了间位取代的双三芳基硼烷5并进行了双倍还原,还原产物52-··并不稳定,发生碳氢活化生成闭壳层的双阴离子72-。我们通过增加硼中心之间的距离,设计和合成了双三芳基硼烷6,并稳定和分离了它的双阴离子62-·。单晶、EPR、SQUID和DFT计算表明,62-··为基态是三线态硼双自由基阴离子。62-·。可以与二苯基二硒醚和三正丁基锡氢发生反应,表现出一定的还原性和夺氢能力。四、我们利用Fe离子配位的方式成功合成并分离了一例硼双自由基8和硼三自由基9,并通过X-射线单晶衍射、EPR和SQUID等表征手段对它们的结构及性质进行了研究。对于化合物8,DFT计算和SQUID测试表明其基态为开壳层单线态,单-三线态能量差仅为0.18 kcal mol-1,容易热激发为三线态;而化合物9为基态是双线态的硼三自由基,可以热激发为四线态,但存在着相对大的四线态和双线态能量差1.4 kcal mol-1。更多还原

【Abstract】 As one of the most important branches of the radical chemistry,diradicals have become an emerging area in organic chemistry,physical chemistry,molecular electronics,and organic spintronics due to their diversity of optical,electrical,and magnetic properties.Most free radicals are very reactive,resulting short lifetimes,oxidation,polymerization,and hydrogen abstraction.The Thiele’s and Chichibabin’s hydrocarbons are two famous examples,which were found slightly later than the triphenylmethyl radical.Stabilization and isolation of the highly reactive species are one of the most important keys to the radical chemistry.Expect for carbon atoms,boron and nitrogen can also serve as excellent spin bearing centers for diradicals.In this thesis,a series of bis(triarylamine)radical cations and boron-containing radical anions,have been isolated and characterized explermently in conjunction with DFT calculations.1.Two bis(triarylamine)dications 12+··and 22+·· bearing bianthracene as the bridging unit,were stabilized and isolated by using weakly coordinating anions.Their geometric and electronic structures were studied by single crystal X-ray diffraction,UV-vis,EPR,and superconducting quantum interference device(SQUID)measurements,in conjunction with DFT calculations.The results show that the change of the groups at para-positions of peripheral aryl rings has a very weak effect on the diradical character,which is dominated by the bianthracene unit.The orthogonal configuration of the anthracene groups reduces the π-conjugation between the two aromatic groups and the dications 12+··and 22+-·· both exhibit very high diradical character.The ground states of the compounds 12+·· and 22+·· are both open-shell singlet,but they have very small singlet and triplet energy gap and can be considered as singlet and triplet degenerated diradicals.2.The boron analogues of Thiele’s and Chichibabin’s hydrocarbons namely 32-and 42-were stabilized and isolated by using steric hindrance effect.Their solid state and electronic structures were investigated.Single-crystal structure characterization,SQUID measurements and DFT calculations show that both 32-and 42-feature a closed-shell ground state.The monoradical anion 3·-has also been isolated,EPR spectroscopic studies and DFT calculations show that the spin density is equally distributed on two boron atoms.3.Meta-substituted 2,6-bis(BMes2)mesitylene(5)and 3,3’-bis(BMes2)bimesitylene(6)were synthesized and two-electron reduced.The reduced specie 52-·· is unstable,and easily undergoes C-H activating of the methyl group leading to the closed-shell product 72-.The reduction of 6 led to the isolation of diradical dianion 6-··,which was characterized by single crystal X-ray crystallography,EPR,SQUID,and DFT calculations.The electron spin density of 62-·· mainly resides on the two boron nuclei and features a triplet ground state.In addition,the reactivity of 62-·· toward PhSeSePh and nBu3SnH was investigated,which is consistent with its radical character.4.Complex Fe(bpyB)3(8,bpyB=5,5’-bis(dimesitylboranyl)-2,2’-bipyridine)and its reduced species[(18-c-6)K(THF)2]·[Fe(bpyB)3](9)were synthesized.Their solid state and electronic structures were investigated by single crystal X-ray crystallography,electron paramagnetic resonance(EPR)and UV-Vis spectroscopy,and SQUID measurements.In 8,two bpyB radical anions are fused by a diamagnetic FeⅡ ion,while in 9 all three bpyB ligands are in the radical state.Complex 8 possesses an open-shell singlet ground state with a singlet-triplet gap of 0.18 kcal mol-1 and complex 9 features an open-shell doublet ground state with a doublet-quartet gap of 1.4 kcal mol-1,as determined by SQUID measurements.The unpaired-electrons in 8 and 9 mainly delocalize over the boron atoms and the bipyrdine moieties with negligible spin density at the iron center.Complex 9 represents the first isolable example of boron-based triradicals.更多还原