Bis-palladium(II) complex of doubly N-confused octaphyrin(1.1.1.1.1.1.1.1): Mobius aromaticity and chiroptical properties

摘要

A novel bis-palladium(II) complex of doubly N-confused octaphyrin (Pd-2-2) adopting a Mobius-twisted topological structure was synthesized and characterized. Due to the effective 36 pi-electronic delocalization over the Mobius-twisted octaphyrin scaffold, characteristic Soret and Q-like absorption features were observed in the near-infrared (NIR) region. However, the complex Pd-2-2 exhibited weak aromatic character attributed to the distinct cross-conjugated resonance contribution as inferred from the H-1 NMR chemical shifts as well as theoretical assessments (e.g. nucleus-independent chemical shift (NICS)). Since the bis-palladium(II) complexation of doubly N-confused octaphyrin 2 imparted significant conformational stability, topologically chiral enantiomers of Pd-2-2 were successfully separated as (P)- and (M)-twisted forms. The resulting isomers revealed relatively large circular dichroism (CD) responses with an absorption anisotropy factor of g(abs) = 0.009 in the NIR region (lambda = 823 nm). In addition, the cyclic voltammogram of Pd-2-2 revealed redox-rich properties due to its large pi-conjugated system.