Isolable Tetragold(0) Clusters with Polarity-Tunable exo-Au-Au Bond via Intramolecular -Aromatization

Intramolecular pi-aromatization is a trait of many organic compounds that enhances the stability of their structures and polarizes related C-C pi bonds. In contrast, rare study is focused on this phenomenon in metal clusters. Many existing homometallic clusters exhibit aromaticity, often characterized by nonpolar metal-metal bonds and a high degree of symmetry. However, synthesizing low-symmetric homometallic clusters with high-polar metal-metal bonds is challenging due to their limited thermodynamic stability. Herein, we report a facile strategy for the synthesis of [Au(mu(2)-ER2)](3)-AuPMe3 (E=Ge, Sn; R-2=1,1,4,4-tetrakis(trimethylsilyl)butane-1,4-diyl) clusters and reveal a novel stabilization mode, intramolecular sigma-aromatization. Our electronic structure analyses show that these low-symmetric clusters possess a ten-electron sigma-aromatic system, which is achieved via intramolecular sigma-aromatization. Moreover, the strength of sigma-aromaticity gives rise to a polarity-tunable exo-Au-Au bond.