摘要
N-Heterocyclic nitrogen Lewis acids are important in synthetic chemistry.Stable cyclic(amino)(aryl)nitrenium cations,cyc-1^(+)-cyc-3^(+),were synthesized by chemical oxidation of aryl azo compounds with different substituents,H and I,at the para positions of the phenyl group.The excited triplet states of cyc-1^(+)-cyc-3^(+) abstract H-atoms step by step to generate radical intermediates cyc-1H^(*+-)cyc-3H^(*+)traced by EPR spectroscopy and products cyc-1H^(2+)-cyc-3H^(2+) characterized by single crystal X-ray diffraction.The Lewis acidity of species cyc-1^(+)-cyc-3^(+) are remote substituent-dependent.Cyc-2^(+)-cyc-3^(+) have much higher acidity than those previously reported congeners based on energies of LUMOs.The electrophilicity enables them to form Lewis adducts with neutral Lewis base Me_(3)P,and to gain one-electron to produce neutral radicals cyc-1^(*)-cyc-3^(*).
基金
the National Key R&D Program of China(Grants 2016YFA0300404 and 2018YFA0306004,X.W.)
the National Natural Science Foundation of China(Grants 21525102 and 21690062,X.W.,and 21901005,W.W.)
the Natural Science Foundation of Anhui Province(Grant 1908085QB48,W W.)
the China Postdoctoral Science Foundation(Grant 2019M651771,W.W.).