Antiaromatic Copper Tetrabenzocorrole:Synthesis,Structures And Antiaromaticity Properties

Aromaticity is one of the most fundamental concepts in the study of cyclicπ-conjugated molecules.According to the Hückel’s rule for cyclic and planar molecules,the 4n+2π-electron systems are aromatic with additional stabilization energy,whereas the 4nπ-electron systems are antiaromatic and destabilized.Antiaromaticity leads to intriguing properties,in particular,the narrow HOMO-LUMO gaps and high electrical conductivity are of great importance in the field of organic electronics.However,the instability nature of antiaromatic molecules still greatly limit their practical applications.It’s very important to design and synthesize stable antiaromatic molecules.Porphyrinoids have emerged as important platforms for the molecular design of stable antiaromatic systems.The 16π-electron conjugated system is the smallest antiaromatic porphyrin,which was proved to sustain stronger antiaromaticity.Corrole is a ring-contracted porphyrin which possess special coordination properties.Copper corrole can form stable radical.The incorporation of fused benzene rings which eliminates the d-πbetween copper and corrole ligand facilitates a purely ligand-based oxidation and effectively stabilizes the antiaromatic skeleton.We designed and synthesised the Cu(II)-tetrabenzocorrole,and the oxidation potential of the corrole radical is really low.A highly air-stable 16π-electron antiaromatic corrole 1~+was obtained for the first time by a facile oxidation of the Cu(II)-tetrabenzocorrole radical.The structure and antiaromatic property of 1~+were characterized and studied.The structure of 1~+was obtained by single crystal X ray diffraction,which revealed the ionic character,the planarity and stability of 1~+.The existence of bivalent copper ion was proved by XPS and ESR,which illustrated that theπ-radical was oxidized.Bond length alternation analysis,~1H NMR,electrochemistry,UV-vis-NIR absorption,MCD and theoretical calculation like nuclear independent chemical shift and anisotropy magnetic induction current density were applied to prove the antiaromatic of 1~+.The theoretical analysis clearly depicted the inner 15-membered-ring main pathway of the strong paratropic ring current.The UV-vis absorption was monitored under room temperature,it showed that there was no change during 60 days which means 1~+is stable under ambit conditions.The redox reaction switch to antiaromatic and aromatic states of corrole radical was studied.The easy synthesis and manipulation in air of this benzo-fused antiaromatic ionic corrole will provide it as a good choice for the design of electronic materials in future.