Chemists synthesize the smallest aromatic ring in history

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Since the discovery of the benzene ring, aromaticity has become an important concept in chemistry. Based on the structure of the benzene ring, a series of **small aromatic rings have been synthesized by the skillful efforts of chemists. Do you know what the smallest aromatic ring is? In fact, this record for the smallest aromatic ring was just set. Recently, a team of chemists led by Professor Holger Braunschweig at the University of Würzburg in Germany successfully synthesized a stable boron-based tricyclic ring (B3 ring), which is the smallest and lightest aromatic ring ever created to date. In addition to helping researchers better understand chemical structures and chemical bonds, these small aromatic rings also hold promising practical applications. These chemists used sodium ions to connect two such B3 rings together in a sandwich-like structure; this unique molecular structure holds promise for the development of semiconductor, superconducting, and magnetic materials. The research findings were published in Angew. Chem. Int. Ed. This team synthesized this B3 cyclic – triborocyclopropenide anion by reacting cyclohexyl-substituted dichloroboramine with metallic sodium in dimethoxyethane solvent. Results from computational chemistry, spectroscopy, and electrochemical studies show that the electronic structure of this B3 ring is consistent with that of classical aromatic carbon compounds, such as cyclopropenyl cations and benzene. “This new synthesis is undoubtedly a major breakthrough and opens up a new direction in boron chemistry,” commented Alexander I. Boldyrev of Utah State University. His research group has carried out a lot of computational work on planar all-boron rings over the past 15 years. You may still remember the debate on aromaticity involving the Nobel laureate Hoffman? Boldyrev belongs to the opposing camp. Aromaticity, as defined by the Hückel rule, is generally confined to the realm of carbon compounds; the few aromatic rings previously identified in non-carbon elements all came from elements heavier than carbon. Chemists have long predicted that planar boron rings from B3 to B15 or larger may also be aromatic. Researchers have long been interested in synthesizing boron rings, but creating separable, stable boron ring compounds represents a significant challenge. The most successful approach so far has been to use laser beams to generate a small number of molecules for study in the gas phase. “Can the concepts and principles of aromaticity be extended to systems based on non-carbon elements? This discovery may help resolve such discussions,” said Boniface Fokwa of the University of California, Riverside. In 2012, Fokwa participated in the synthesis of the first separable solid compound with a planar boron ring, Ti7Rh4Ir2B8. “The discovery of this new planar B3 ring compound strongly suggests that it may also be stable in solid compounds,” said Fokwa. “We hope that, building on this, exciting new functional materials can be discovered.” ”