Olefin–Borane Interactions in Donor–π–Acceptor Fluorophores that Undergo Frustrated‐Lewis‐Pair‐Type Reactions

Abstract

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.

Efficient Narrowband Circularly Polarized Light Emitters Based on 1,4‐B,N‐embedded Rigid Donor–Acceptor Helicenes

“…Furthermore, we found that all three compounds exhibit coordination to trace residual moisture in solvents upon cooling. [22] Coordination was observed even in solvents determined to be dry via Karl Fischer titration (Supporting Information Section S3D).…”

Efficient Narrowband Circularly Polarized Light Emitters Based on 1,4‐B,N‐embedded Rigid Donor–Acceptor Helicenes

“…The absence of TADF in 3‐ C 2 , 3‐ C s , and 4‐ C 1 is due to significantly large Δ E ST than those for 1 and 2 . Furthermore, we found that all three compounds exhibit coordination to trace residual moisture in solvents upon cooling [22] . Coordination was observed even in solvents determined to be dry via Karl Fischer titration (Supporting Information Section S3D).…”

“…Furthermore, we found that all three compounds exhibit coordination to trace residual moisture in solvents upon cooling. [22] Coordination was observed even in solvents determined to be dry via Karl Fischer titration (Supporting Information Section S3D). To probe the charge transfer (CT) characteristics of the excited state, we performed additional absorption and emission measurements for 3-C 2 , 3-C s , and 4-C 1 in non-polar 2-methylpentane and more polar 2-methyltetrahydrofuran (2-MeTHF) solvents (Figure 3).…”

Skeletal rearrangement of a boron-containing annulenic molecule into a macrocycle bridged by an electronically stabilized boron cation

“…2 Although borane-olefin complexes had been considered as weakly interacting van der Waals complexes, 3,4 it has recently been shown that they can affect the structure and reactivity of molecular systems having borane and olefinic moieties in close proximity. 5–8 Yamaguchi and coworkers reported a reversible FLP-type addition reaction of Lewis bases to an olefin-containing triarylborane derivative with a structure where borane and olefin moieties are close to each other. 6 Braunschweig and coworkers revealed that the boron-bridged boranorbornadiene derivatives formed in the reaction between a borole and an alkyne derivative are in equilibrium with borepins and boranorcaradienes in solution, due to intramolecular complexation between the borane moieties and the π-system.…”

“…5–8 Yamaguchi and coworkers reported a reversible FLP-type addition reaction of Lewis bases to an olefin-containing triarylborane derivative with a structure where borane and olefin moieties are close to each other. 6 Braunschweig and coworkers revealed that the boron-bridged boranorbornadiene derivatives formed in the reaction between a borole and an alkyne derivative are in equilibrium with borepins and boranorcaradienes in solution, due to intramolecular complexation between the borane moieties and the π-system. 7 There is growing understanding of interactions between borane and unsaturated C–C bonds in terms of their chemical reactivities.…”