Phenylpyridyl‐Fused Boroles: A Unique Coordination Mode and Weak B−N Coordination‐Induced Dual Fluorescence. (14th January 2021)

• Record Type: Journal Article
• Authors: He, Jiang; Rauch, Florian; Friedrich, Alexandra; Krebs, Johannes; Krummenacher, Ivo; Bertermann, Rüdiger; Nitsch, Jörn; Braunschweig, Holger; Finze, Maik; Marder, Todd B.
• Is Part Of: Angewandte Chemie. Volume 133:Number 9(2021)
• Page Start: 4883
• Page End: 4890
• Publication Date: 2021-01-14
• Subjects: boroles -- dual fluorescence -- equilibrium -- tetramers -- weak intermolecular coordination; Chemistry -- Periodicals; 540
• DOI: 10.1002/ange.202013692
• Languages: English
• ISSNs: 0044-8249

Abstract

Abstract: Using 4‐phenylpyridine or 2‐phenylpyridine in place of biphenyl, two electron‐poor phenylpyridyl‐fused boroles, [TipPBB1]4 and TipPBB2 were prepared. [TipPBB1]4 adopts a unique coordination mode and forms a tetramer with a cavity in both the solid state and solution. The boron center of TipPBB2 is 4‐coordinate in the solid state but the system dissociates in solution, leading to 3‐coordinate borole species. Compared to its borafluorene analogues, the electron‐accepting ability of TipPBB2 is largely enhanced by the pyridyl group. TipPBB2 exhibits dual fluorescence in solution due to an equilibrium between free TipPBB2 and a weak intermolecular coordination adduct with a second molecule. This equilibrium was further investigated by low‐temperature NMR spectroscopy and photophysical studies. Theoretical studies indicate that the highest occupied molecular orbital (HOMO) of TipPBB2 localizes at the Tip group, in contrast to its borafluorene derivatives, wherein the HOMOs are localized on the borafluorene cores. Abstract : Phenylpyridyl‐fused boroles [TipPBB1]4 and TipPBB2 were synthesized and their properties investigated. [TipPBB1]4 forms a tetramer in both the solid state and solution. TipPBB2 contains a 4‐coordinate boron atom in the solid state but dissociates to give a 3‐coordinate boron species in solution. TipPBB2 shows interesting temperature‐dependent dual fluorescence in solution because of the equilibrium between 3‐ and 4‐coordinate boron species due to weak N⋅⋅⋅B intermolecular coordination.