Supporting InforDynamic N-->B Coordination and Anion-selective Turn-On Fluorescence in Oxadiazole-functionalized Organoboranes

Supporting information for the research article by the above title. Abstract: versatile route for the preparation of chemically and electronically diverse Mes2BPh-based boranes (Mes = mesityl, 2,4,6-trimethylphenyl) is presented that makes use of the conversion of a single tetrazolyl-functionalized borane precursor (2H) into a boranes bearing substituted oxadiazolyl-groups. A series of eight boranes (4a–4g) was prepared with functional groups on the 5-position of the oxadiazole ranging from electron donating (4a: 4-Me-phenyl, 4b: 4-MeO-phenyl,..) to strongly electron withdrawing (4d: 4-O2N-phenyl, 4e: 3,5-bis(CF3)-phenyl, 4h: CF3) and a bifunctionalized example bearing two Mes2B-moieties (4g). A full characterization of the optical, electrochemical and electronic properties, both experimentally and by DFT calculations was carried out. Our investigation shows the boranes to exhibit dynamic equilibria between closed intramolecularly NB-coordinated and open non-coordinated conformers, as indicated by variable temperature NMR, 11B NMR and anion binding studies with F- and CN-. The anion binding studies reveal substantial differences in the fluorescence response of the compounds ranging from differing degrees of quenching to fluorescence shift (4g) and enhanced emission 4c (4-OMe-phenyl). These results show that this synthetic strategy allows to easily create series of compounds with incrementally varied optical properties and Lewis acidities that may serve as dye, catalysts or chemical sensors.