Olefin-borane π-complexes have been postulated as intermediates for the addition of frustrated Lewis pairs (FLP) to olefins. In the present study, we have employed this weak interaction to modulate the electronic properties of boron-based π-electron materials. A series of donor-π-acceptor (D-π-A) fluorophores that contain an alkenyl-bridged diarylboryl group is synthesized. A crystallographic analysis revealed that the olefin and boron moieties are held in close proximity. Upon addition of a Lewis base to a solution of these D-π-A fluorophores, an FLP-type addition occurs with concurrent significant changes in the absorption and emission properties. The FLP-type reaction shifts the reaction site from the Lewis-acidic boron atom to a carbocationic center, and thereby even facilitates a reaction with bulky Lewis bases. For example, a tricyclohexylphosphine adduct thus generated exhibits temperature-dependent reversible dissociation/association behavior. These results provide a design strategy for stimuli-responsive emissive boron-based materials.
While the range of accessible borylenes has significantly broadened over the last decade, applications remain limited. Herein, we present tricoordinate oxy‐borylenes as potent photoreductants that can be readily activated by visible light. Facile oxidation of CAAC stabilized oxy‐borylenes (CAAC)(IPr2Me2)BOR (R=TMS, CH2CH2C6H5, CH2CH2(4‐F)C6H4) to their corresponding radical cations is achieved with mildly oxidizing ferrocenium ion. Cyclovoltammetric studies reveal ground‐state redox potentials of up to −1.90 V vs. Fc+/0 for such oxy‐borylenes placing them among the strongest organic super electron donors. Their ability as photoreductants is further supported by theoretical studies and showcased by the application as stoichiometric reagents for the photochemical hydrodehalogenation of aryl chlorides, aryl bromides and unactivated alkyl bromides as well as the detosylation of anilines.
Obwohl sich das Spektrum verfügbarer Borylene in den letzten zehn Jahren erheblich erweiterte, sind ihre Anwendungen nach wie vor limitiert. In dieser Arbeit präsentieren wir dreifach koordinierte Oxyborylene als potente Photoreduktionsmittel, die durch sichtbares Licht aktiviert werden können. Die Einelektronenoxidation der CAAC‐stabilisierten Oxyborylene (CAAC)(IPr2Me2)BOR (R=TMS, CH2CH2C6H5, CH2CH2(4‐F)C6H4) zu den entsprechenden Radikalkationen wird mit Ferroceniumionen als Oxidationsmittel realisiert. Cyclovoltammetrische Studien zeigen für diese Oxyborylene Grundzustands‐Redoxpotentiale von bis zu −1.90 V vs. Fc+/0, womit sie zu den stärksten organischen Super‐Elektronendonoren gehören. Ihre Eigenschaften als Photoreduktionsmittel werden durch theoretische Studien untermauert und durch die Anwendung als stöchiometrische Reagenzien für die mit sichtbarem Licht vermittelte Detosylierung von Anilinen sowie Hydrodehalogenierung von Arylchloriden, Arylbromiden und nicht aktivierten Alkylbromiden unter Beweis gestellt.
Olefin-borane π-complexes have been postulated as intermediates for the addition of frustrated Lewis pairs (FLP) to olefins. In the present study, we have employed this weak interaction to modulate the electronic properties of boron-based π-electron materials. A series of donor-π-acceptor (D-π-A) fluorophores that contain an alkenyl-bridged diarylboryl group is synthesized. A crystallographic analysis revealed that the olefin and boron moieties are held in close proximity. Upon addition of a Lewis base to a solution of these D-π-A fluorophores, an FLP-type addition occurs with concurrent significant changes in the absorption and emission properties. The FLP-type reaction shifts the reaction site from the Lewis-acidic boron atom to a carbocationic center, and thereby even facilitates a reaction with bulky Lewis bases. For example, a tricyclohexylphosphine adduct thus generated exhibits temperature-dependent reversible dissociation/association behavior. These results provide a design strategy for stimuli-responsive emissive boron-based materials.
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