Synthese, Struktur, Elektrochemie und optische Eigenschaften von alkinylfunktionalisierten 1,3,2‐Diazaborolen und 1,3,2‐Diazaborolidinen

Abstract

Syntheses, Structures, Electrochemistry and Optical Properties of Alkyne‐Functionalized 1,3,2‐Diazaboroles and 1,3,2‐Diazaborolidenes The reaction of 2‐bromo‐1,3‐ditert‐butyl‐2,3‐dihydro‐1H‐1,3,2‐diazaborole (3) with lithiated tert‐butyl‐acetylene and lithiated phenylacetylene affords the 2‐alkynyl‐functionalized 1,3,2‐diazaboroles 4 and 5 as a thermolabile colorless oil (4) or a solid (5). Similarly 2‐bromo‐1,3‐diethyl‐2,3‐dihydro‐1H‐1,3,2‐benzodiazaborole (6) was converted into the crystalline 2‐alkynyl‐benzo‐1,3,2‐diazaboroles 7 and 8 by treatment with LiC≡C–tBu or LiC≡CPh, respectively. 2‐Ethynyl‐1,3‐ditert‐butyl‐2,3‐dihydro‐1H‐1,3,2‐diazaborole (2) was metalated with tert‐butyl‐lithium and subsequently coupled with 2‐bromo‐1,3,‐ditert‐butyl‐2,3‐dihydro‐1H‐1,3,2‐diazaborole (3) to afford bis(1,3‐ditert‐butyl‐2,3‐dihydro‐1H‐1,3,2‐diazaborol‐2‐yl)acetylene (9) as thermolabile colorless crystals. Analogously coupling of the lithiated species with 6 or with 2‐bromo‐1,3‐ditert‐butyl‐1,3,2‐diazaborolidine (11) gave the unsymmetrically substituted acetylenes 10 or 12, respectively, as colorless solids. Compounds 4, 5, 7–10 and 12 are characterized by elemental analyses and spectroscopy (IR, 1H‐, 11B{1H}, 13C{1H}‐NMR, MS). The molecular structures of 5, 8 and 9 were elucidated by X‐ray diffraction analyses.

Synthetic, structural, photophysical and computational studies on 2-arylethynyl-1,3,2-diazaboroles

“…The computed oscillator strengths are in accord with the observed extinction coefficients for all diazaboroles 1-5. for related diazaboroles studied here and elsewhere. 16 What is clearly evident from the computational results is that, in contrast to well-known BAr 2 systems (e.g. Ar = Mes), in which the BAr 2 unit serves as a strong π-acceptor, the 10 π-electron benzodiazaborole unit, isoelectronic with indenyl anion, is electron rich.…”

“…Several compounds related to 1 but containing three-coordinate boron attached to a phenylethynyl group have been structurally characterised. 15,16 However, aside from the molecular structures of 1-3 and 5 herein, there is only one set of crystal structures from which we can examine the structural effects of substituents on the phenyl group of the B-C≡C-Ar moiety, namely Mes 2 BC≡CMes and Mes 2 BC≡CC 6 H 4 NMe 2 , which may be viewed as Mes 2 B analogues of 2 and 5. 3,17 As in 2 and 5, the bonds in the B-C≡C-C Ar moiety are essentially unaffected by whether the substituent is Me or NMe 2 .…”

Diazaborolyl-boryl push–pull systems with ethynylene–arylene bridges as ‘turn-on’ fluoride sensors

“…Bond lengths and bond angles within the benzodiazaborole part of 3 are similar to those of numerous diazaboroles studied before. 17,19,22,[25][26][27] The molecule 12 may be described as a benzodiazaborole which is connected with a 2-thienylethynyl unit via the B(1)-C(11) single bond of 1.520(3) Å. Both heterocycles are linked by an essentially linear ethynyl bridge with a triple bond C(11)-C(12) bonds of 1.207(3) Å and angles B(1)-C(11)-C(12) and C(11)-C(12)-C(13) of 176.4(2)° and 178.2(3)°, respectively.…”

“…For synthetic reasons the 1,3-diethyl-1,3,2-benzodiazaborole unit is the most frequently employed representative, and compounds containing this group as a substituent are moderately air-stable. 16,[22][23][24][25][26][27] As the BMes 2 group is known as an effective acceptor (A) and the benzodiazaborolyl unit has been suggested to be a π-donor (D) 27 the novel "push-pull"-systems [D-bridge-A] with 1,4-phenylene-, 4,4'-biphenylene-, 2,5-thiophene-and 5,5'-dithiophene-scaffolds (I-IV, Chart I) have been investigated recently. 28 Photophysical studies on these compounds reveal blue-green fluorescence and Stokes shifts for the first three representatives of 7820-9760 cm -1 in THF, whereas the Stokes shift for the last compound is significantly smaller (5510 cm -1 in THF).…”

The role of 2,3-dihydro-1-H-1,3,2-diazaboroles in luminescent molecules

“…Considering the three conformers of derivative 90, decreasing torsion angles at the borolyl units and the phenyl rings were reflected in successive shortening of the C1 C2 bond. Basically, the orientation of the aryl groups with respect to the C1 C2 vector influences the C1 C2 bond lengths [79].…”