Benzoborirene: A Starting Point to Metallaboraarenes and Diazaborole-fused Boroles

• Applicant: Professor Dr. Qing Ye
• Subject Area: Inorganic Molecular Chemistry - Synthesis and Characterisation
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 520987585

Benzoborirene, a formal borylene-benzyne complex, features a 2π Hückel-aromatic borirene ring that is fused to a 6π Hückel-aromatic benzene ring, and thus constituting an intriguing 6π-2 π bicyclic and highly strained platform. The solution-phase synthesis of isolable benzoborirenes is of great challenge that has not been addressed until very recently. Our laboratory reported the first successful synthesis by the Zr-B exchange reaction between a η2-benzyne zirconocene complex and an amino(dihalo)borane. In this project, we intend to apply this synthetic approach to synthesize a variety of benzoborirenes by variation of the substituents of the benzyne intermediate and the exocyclic substituent on boron (subproject A). The enrichment of the benzoborirene family is particularly urgent, as this is essential for the assessment of the steric as well as the electronic effect of the substituents on the aromaticity, structure, and reactivity. On the other hand, metallaarenes and diboraarenes are both striking compounds owing to numerous fascinating aspects, which span from the fundamentally significant concepts (e.g. Hückel/Möbius aromaticity, antiaromaticity, Lewis acidity), over the rich reaction chemistry, to potential applications in catalysis and material science. However, metallaboraarene chemistry is still a gaping area. Our preliminary results demonstrated the application of benzoborirene in the synthesis of a Zr,B-9,10-anthracene complex, in which the CH units at the 9- and 10-position of anthracene are replaced with tricoordinate boron and a zirconocene fragment, respectively. In this project, we aim at initiating the metallaboraarene chemistry by applying/modifying the synthetic strategy for the B,Zr-9,10-anthracene. The bonding situations, aromaticity, physical properties, and reactivity, in particular that associated with small molecule activation, will be systematically studied (subproject B). Furthermore, our preliminary study demonstrated the synthesis of benzoborole diamide complexes from benzoborirene. In this project, we utilize the diamide complexes to synthesize the heretofore unknown diazaborole-fused boroles. The effect of annulation on antiaromaticity, Lewis acidity, electrochemistry, and photophysical properties will be investigated (subproject C).

• DFG Programme: Research Grants
• International Connection: China (Hong Kong)
• Cooperation Partner: Professor Dr. Zhenyang Lin