Levitskiy Oleg A, Dulov Dmitry A, Bogdanov Alexey V, Grishin Yury K, Nefedov Sergey E, Magdesieva Tatiana V
Department of Chemistry, Lomonosov Moscow State University, Leninskie Gory 1/3, 119991, Moscow, Russian Federation.
Kurnakov Institute of General and Inorganic Chemistry, Russian Academy of Sciences, Leninsky prosp. 31, 119991, Moscow, Russian Federation.
Chemistry. 2020 May 26;26(30):6793-6804. doi: 10.1002/chem.202000165. Epub 2020 Apr 17.
The α-methylcyclopropyl (MCP) group with conformationally dependent electronic properties is suggested as an additional structural "instrument" for stabilization of both open-shell and ionic states of diarylnitroxides, to be used as "ambipolar" redox active materials. New MCP-substituted diphenylnitroxides (fully characterized by electrochemical, spectral, and X-ray data) are the most stable nitroxides of the diaryl type known to date [τ in benzene exceeds three months (2310 h)]. The radicals are capable to reversible oxidation and reduction, yielding stable oxoammonium cations and aminoxyl anions. DFT investigation of the electronic structure and geometry of the compounds confirmed the conformational switching of the cyclopropyl orientation relative to the adjacent aromatic π system is dependent on the nitroxide's redox state. Additional through-space stabilizing interaction between the π-acceptor orbital of the NO moiety and the cyclopropyl "banana" bond orbital was also detected, highlighting its good hyperconjugative ability. The estimated σ(para) value (-0.32) confirms its strong electron-donating properties.
具有构象依赖性电子性质的α-甲基环丙基（MCP）基团被提议作为一种额外的结构“工具”，用于稳定二芳基氮氧化物的开壳态和离子态，用作“双极性”氧化还原活性材料。新型MCP取代的二苯基氮氧化物（通过电化学、光谱和X射线数据进行了全面表征）是迄今为止已知的二芳基类型中最稳定的氮氧化物[在苯中的半衰期超过三个月（2310小时）]。这些自由基能够进行可逆的氧化和还原，生成稳定的氧鎓阳离子和氨基氧阴离子。对这些化合物的电子结构和几何结构进行的密度泛函理论（DFT）研究证实，环丙基相对于相邻芳族π体系的取向的构象转换取决于氮氧化物的氧化还原状态。还检测到NO部分的π受体轨道与环丙基“香蕉”键轨道之间额外的空间稳定相互作用，突出了其良好的超共轭能力。估计的σ(对位)值（-0.32）证实了其较强的给电子性质。
