N‐Heterocyclic Carbene Boranes as Electron‐Donating and Electron‐Accepting Components of π‐Conjugated Systems

Abstract

Give and take: The introduction of NHC-borane moieties to thiophene-based π skeletons endows a zwitterionic character, which makes the π system electron-donating, while the NHC ring acts as an electron-accepting moiety. The NHC-borane-substituted thiophene underwent a clean photoisomerization with a drastic color change, however, the expanded bithiophene derivatives were inert to this photoreaction, showed low oxidation potentials, and formed a slipped π-stacked array in the crystal.

Reversible 1,1‐Hydroboration: Boryl Insertion into a CN Bond and Competitive Elimination of HBR2 or RH

“…Organoboron compounds are an important class of molecules,w hich can be found in an umber of important fields [1] including hydrogen storage, [2] optoelectronic devices, [3][4] sensors, [5] and organic synthesis. [6] Of the many organoboron species,b oranes (particularly those of the form HBR 2 )h ave long been studied for their use in the functionalization of alkenes and alkynes by 1,2-hydroboration which was originally pioneered by Herbert C. Brown.…”

Geometric and Electronic Structures of Boron(III)‐Cored Dyes Tailored by Incorporation of Heteroatoms into Ligands

“…[12] Compound 1 shows a maximum absorption peak at 348 nm with a weak-shoulder absorption at 320 nm, which is due to a p-p* transition of the aromatic backbone. [15] In addition, a broad absorption maximum at longer wavelength (588 nm) is tentatively assigned to an intramolecular charge transfer from the donor perimidine to the ac- ceptor quinoline parts on the basis of the measured negative solvatochromic effect ( Figure S13). The blue shift of this absorption band in a solvent with higher polarity suggests that the ground state is more polar than the excited state for 1, [16] coincident with the molecular D-A structure.…”

Dearomatizing and Derivatizing a Mesityl Group on Boron by One‐Pot Photoisomerization and [4+2] Diels–Alder Addition

“…The one-pot procedure used in the presenti nvestigation (Scheme 2) involves initial photochemical conversion of 1-3 to their respective dark borirane isomers 1a-3a in J-Young NMR tubes, in benzene or toluene, as we have described previously. [5] This photochemical conversion can be readily tracked by NMR spectroscopy.U pon full conversiont o1a-3a,v ariousd ienophiles were examined for their reactivity towards the cyclohexadienyl units therein. Amongt he alkyne dienophiles we examined, dimethyl acetylenedicarboxylate (DMAD) provedt ob et he most reactive toward 1a-3a,s howing appreciable reactions at ambient temperature, which may be attributed to its relatively high electrophilicity toward the electron-rich dienyl unit.…”

“…The product could be described as ab oratanorcaradiene (BNCD), a7 -borabicyclo[4.1.0]hepta-2,4-diene, or ab oriranefused cyclohexadiene (e.g., 1a-3a in Scheme 1). [5] Compared to the chelate starting materials (e.g., 1-3 in Scheme 1), which are thermally stable and chemically inert, the species 1a-3a are much higher in energy (by ca. 30 kcal mol À1 )a nd their borirane-cyclohexadienyl unit is highly electron-rich and reactive towardso xygen.…”