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

Abstract

A novel bis-palladium(II) complex of doubly N-confused octaphyrin (Pd[Formula: see text]-2) adopting a Möbius-twisted topological structure was synthesized and characterized. Due to the effective 36[Formula: see text]-electronic delocalization over the Möbius-twisted octaphyrin scaffold, characteristic Soret and Q-like absorption features were observed in the near-infrared (NIR) region. However, the complex Pd[Formula: see text]-2 exhibited weak aromatic character attributed to the distinct cross-conjugated resonance contribution as inferred from the 1H NMR chemical shifts as well as theoretical assessments ([Formula: see text] 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[Formula: see text]-2 were successfully separated as ([Formula: see text]- and ([Formula: see text]-twisted forms. The resulting isomers revealed relatively large circular dichroism (CD) responses with an absorption anisotropy factor of [Formula: see text] [Formula: see text] 0.009 in the NIR region ([Formula: see text] 823 nm). In addition, the cyclic voltammogram of Pd[Formula: see text]-2 revealed redox-rich properties due to its large [Formula: see text]-conjugated system.