Biomimetic all-metal Pd₁₁ helicene.

Abstract

Since their discovery in the early 20th century, helicenes have emerged as a distinctive class of polycyclic aromatic compounds with rigid, screw-shaped chiral frameworks and substantial photoelectrical properties. Over the past century, this family has expanded to include diverse heterohelicenes and functional derivatives. In sharp contrast, the rational construction of all-metal helicenes, in which the helical backbone is entirely composed of metal elements, remains a formidable synthetic challenge because of the difficulty of simultaneously controlling metal coordination geometry, helical propagation, and configurational stability. Herein, we report a stibine/thiolate-protected metallic helicene, Pd₁₁(PhSb)₂(AdmS)₁₀, denoted as an antimony (Sb)-centered [3]Pd-helicene cluster. The Pd₁₁ framework features a Pd₃ triangle ortho-fused with two μ₆-Sb-centered Pd₆ rings, giving rise to an unprecedented slightly open-mouthed, scallop-like all-metal helicene architecture. Two 7-center-2-electron (7c-2e) σ bonds are localized on the Sb-centered Pd₆ rings, stabilizing the helical all-metal skeleton. This metallic helicene can undergo structural "unfolding" through complete opening of the fused Pd₆ rings, affording a chiral homolog, Pd₁₁SCl(PhSb)₂(AdmS)₁₁. Notably, the Sb-centered [3]Pd-helicene cluster exhibits an exceptional electrocatalytic activity for two-electron oxygen reduction reaction, the reason for which was disclosed by operando infrared spectroscopy analysis and density functional theory calculations. This work represents an important advance in pursuit of all-metal helicene and opens avenues for their rational synthesis and functional exploitation.