Azadistibiridines and stabilised-iminobismuthane: reactivity of small inorganic rings in heavy main group chemistry

Abstract

Small organic rings are important molecular entities that have long played a crucial role in organic synthesis and medicinal chemistry. Similarly, small inorganic rings have shown promise in promoting bond activation and, in some cases, catalysis, although their synthesis is significantly more challenging. Here, we present a detailed experimental and theoretical investigation of three-membered heterocycles, azadistibiridines (2a–2d), synthesised via cycloaddition of a distibene (Sb₂Tbb₂) with various azides. Additionally, for the first time, we were able to extend this protocol to dibismuthene (Bi₂Tbb₂), usually a more inert fragment, generating an iminobismuthane dimer (4a), showing divergent reactivity compared to that of distibene. Taking advantage of the strain imposed by these rings, we have been able to explore the reactivity of both classes of compounds, leading to the isolation of a ring-expanded product with GeBr₂ (5) and a rare example of NHC-supported iminobismuthane (6). These findings represent a significant theoretical and practical advancement in main group chemistry where small inorganic rings have been used as tools to enhance the reactivity of heavy pnictogen multiple bonds.