Expedient Synthesis of Oxaboracyclic Compounds Based on Naphthalene and Biphenyl Backbone and Phase‐Dependent Luminescence of their Chelate Complexes

Abstract

The approach to a series of six‐ and seven‐membered oxaboraheterocycles based on naphthalene or biphenyl backbones was developed. The key synthetic step involved Br/Li exchange in respective potassium (bromoaryl)trifluoroborates followed by quenching with selected electrophiles (CO2, DMF, Me2Si(H)Cl) and hydrolytic workup. Two ring‐expanded benzoxaborole congeners were obtained by an additional reduction step with LiAlH4 or NaBH4. The obtained boracyclic compounds were characterized in detail by NMR spectroscopy and single‐crystal X‐ray diffraction. Specifically, biphenyl‐based systems show dynamic behaviour interpreted in terms of inversion of non‐planar seven‐membered boraheterocycles. The acidity of the obtained compounds varies very strongly (pKa ranges from 3.1–9.6) depending on their structure. Due to the enhanced boron Lewis acidity, selected compounds were used as a basis for luminescent complexes with 8‐hydroxyquinoline. A strong phase‐dependent variation of emission‐band maximum (480–527 nm) and photoluminescence quantum yield (10–95 %) was observed, which was rationalized in terms of specific aggregation effects.

Highly electron-deficient 3,6-diaza-9-borafluorene scaffolds for the construction of luminescent chelate complexes

“…0.3–0.5 units and thus 5 is significantly more acidic than boronophthalide (p K a = 2.0). 8 a ,10 However, it should be noted that 5 is poorly soluble in water which can be rationalized by its strong aggregation as the molecular chains are further interconnected by O–H⋯N interactions ( d N⋯O = 2.833(2) Å) producing a very compact and highly symmetric HB network (Fig. 1b).…”

“…The estimated energy of this HB is −84 kJ mol −1 (calculation details are provided in the ESI † ) and the amount of electron density at the bond critical point is ρ = 0.73 e·Å −3 which is comparable to the values found in very strong charge-assisted HBs. 9 The structure 5 is related to the oxonium acid structures of boronophthalide, 8 a 3,4,5,6-tetrafluorophenylene-1,2-diboronic acid 8 c and 1-hydroxy-1 H ,3 H -naphtho[1,8- cd ][1,2]oxaborinin-3-one, 10 which also feature comparably strong intermolecular HB interactions ( d O⋯O = 2.424–2.486 Å, Table S2.3, ESI † ) correlating with high Brønsted acidity (p K a = 2–3). Indeed, p K a values for 2 and 5 are 2.4 and 1.4, respectively, as determined by potentiometric titration with 0.1 M aq.…”

Screening of organoboron compounds as potential ionophores in a miniaturized ITIES cell.

“…LiCl (99%, Merck), tetramethylammonium (TMA) chloride (≥ 99%, Fluka), 1,2-dichloroethane (DCE) (pure p.a., Chempur), ,,-trifluorotoluene (TFT) (anhydrous ≥ 99%, Merck) and diphenyl ether (Merck). Organoboron compounds (OBC) including arylboronic acids (2-6, 8) 39,40,41,42,43 , oxaboroles (10-14) 44,45,46 , cyclic borinic acids, namely dibenzoborinines (15-17) 47,48, and triarylborane 18 48 were available from our previous studies. Phenylboronic acid (1) was purchased from Merck.…”

Fusion of Aza‐ and Oxadiborepins with Furans in a Reversible Ring‐Opening Process Furnishes Versatile Building Blocks for Extended π‐Conjugated Materials

“…[ 6 , 9 , 10 , 11 ] The same is true for compounds featuring the structurally and electronically related BOB fragments. [ 6a , 12 , 13 , 14 , 15 ] In 2018, Yan et al. reported on the synthesis of dithieno[3,2‐ c :2’,3’‐ e ][1,2,7]oxadiborepin derivatives ( D ).…”

“…On the other hand, relatively few BNB‐doped aromatics have been developed and investigated for their optoelectronic properties so far [6,9–11] . The same is true for compounds featuring the structurally and electronically related BOB fragments [6a,12–15] . In 2018, Yan et al.…”