Synthesis and Properties of C_2h-Symmetric BN-Heteroacenes Tailored through Aromatic Central Cores

Abstract

The 2-fold successive electrophilic borylation on one aromatic central core led to a series of C(2h)-symmetric BN-heteroacenes in excellent yields. For the first time, we introduced trimethylsilyl (TMS) as either leaving group or oriented group for efficiently improving the preparation of BN-embedded polycyclic aromatic hydrocarbons (PAHs). The physical properties of the as-synthesized BN-heteroacenes in either solid state or solution can be finely tuned through the position isomerization or the fused ring numbers of the aromatic central core.

Intramolecular (directed) electrophilic C–H borylation

“…This was attributed to the challenge of doubly borylating the central 1,4-phenylene ring with the first borylation installing a mesomerically deactivating boron moiety. 49 Consistent with previous reports, directed C-H borylation was more readily achieved when the unit being borylated was a more nucleophilic congener of H, e.g. with a thienyl derivative as the central aromatic unit being borylated.…”

Exploration of Syntheses and Functions of Higher Ladder-type π-Conjugated Heteroacenes

“…The same group developed a series of C 2h -symmetry BN-embedded LHAs with a number of different central aromatic cores by employing 2-fold electrophilic borylation reaction (compounds 46-48). 67,68 The crystal structures of these molecules suggests that the B-N bond lengths for all three compounds were in the range of 1.409-1.416 Å , which is indicative of a typical double-bond character. However, all the compounds showed a strong absorption in the UV region, suggesting that highly electronegative B=N double bonds contributed little toward electronic delocalization in the conjugated system.…”

“…64,65 Recently, Feng and coworkers developed a synthetic strategy based on the cyclization of N-directed aromatic borylation toward a series of BN-embedded LHAs. 66,67 2,5-bis-Benzothiophene-substituted phenylenediamine intermediates were prepared by a Suzuki coupling reaction. These intermediates were then treated with excess PhBCl 2 and triethylamine catalyst to bring about a smooth ring-closing reaction (Scheme 15).…”

Probing a General Rule towards Thermodynamic Stabilities of Mono BN‐doped Lower Polyenes

“…Based on atomic radii, the bond length for a B−N bond is 1.58 Å, whereas it is 1.40 Å for a B=N bond . In our calculations, the C=C and C−C bond lengths in butadiene are 1.332 and 1.461 Å.…”