BN‐Embedded Polycyclic Aromatic Hydrocarbon Oligomers: Synthesis, Aromaticity, and Reactivity

Abstract

BN‐embedded oligomers with different pairs of BN units were synthesized by electrophilic borylation. Up to four pairs of BN units were incorporated in the large polycyclic aromatic hydrocarbons (PAHs). Their geometric, photophysical, electrochemical, and Lewis acidic properties were investigated by X‐ray crystallography, optical spectroscopy, and cyclic voltammetry. The B−N bonds show delocalized double‐bond characteristics and the conjugation can be extended through the trans‐orientated aromatic azaborine units. Calculations reveal the relatively lower aromaticity for the inner azaborine rings in the BN‐embedded PAH oligomers. The frontier orbitals of the longer oligomers are delocalized over the inner aromatic rings. Consequently, the inner moieties of the BN‐embedded PAH oligomers are more active than the outer parts. This is confirmed by a simple oxidation reaction, which has significant effects on the aromaticity and the intramolecular charge‐transfer interactions.

BN‐Embedded Polycyclic Aromatic Hydrocarbon Oligomers: Synthesis, Aromaticity, and Reactivity

“…Moreover, the bond lengths of C10 À C11 (1.436(3) )a nd C33 À C34 (1.434(3) )i nt he outer azaborine rings are slightly shorter than those of C4ÀC5 (1.443 (3) )and C23ÀC25 (1.442 (3) ) in the inner azaborine rings,i ndicating the different charge delocalization effects and aromaticity between the outer and inner azaborine rings.F urthermore,M e-BN2 has four cove regions.T wo types of distortions can be found due to the different steric hindrances of hydrogen atoms on the benzene and thiophene rings.The dihedral angle between the benzene rings fused on the azaborine units are 338 8 and 368 8,r espectively,w hile the dihedral angles between the two thiophene rings are 88 8 and 178 8,respectively (Figure 4b). Additionally, P- [30] Angewandte Chemie Forschungsartikel and M-helical structures (Figure 4c)can be also found in the single crystal of Me-BN2. Unlike BN1, the P-a nd M-helical structures in Me-BN2 form separated arrays.T he p-p distances in the two arrays are both 3.69 (Figure 4d), which is slightly higher than that in BN1 and owing to the more twisted structures of Me-BN2.…”

“…Figure 9. a) ORTEP drawing of Me-BN2-O 2 with ellipsoids set at 50 % probability.b)Selected bond lengths for Me-BN2-O 2 .c )P-and Mhelical structures of Me-BN2-O 2 .d)Crystal packing of Me-BN2-O 2(Hydrogen atoms are omitted for clarity) [30]. …”

Mono- and Dinitro-BN-Naphthalenes: Formation and Characterization

“…BN aromatics have been widely investigated in recent years since the materials pos sess attractive physical and chemical properties and hold potential applications in the light-emitting polymer [1][2][3][4][5][6][7][8][9][10][11][12], semiconductor [13][14][15][16][17], and other research fields [18][19][20][21][22][23][24][25][26][27][28][29] however, there have been relatively few reports on the synthesis of nitrated BN aromatics Thus far, only five mononitro-BN aromatics have been reported [30,31]. Dewar and their co-workers [30, in 1959, reported the first nitration of a BN aromatic, BN-phenanthrene (BNP), yielding a mixture of mononitro-substituted BNPs (1).…”

“…This is a typical procedure for generating AcONO2 in organic synthesis, but in our hands, AcONO2 generated by this method failed to nitrate BN-naphthalene, giving only decomposition. Fang and co-workers [31], in 2017, successfully nitrated azaborazines to nitro-azaborazines (2) and BNN to 3-nitro-BNN (3) using AcONO2 generated from hy drated metal nitrates and acetyl chloride (AcCl) in CH2Cl2. The nitration provided highly positional selectivity at the para-position relative to the boron atom, but the nitration did not produce higher nitrated BN derivatives even at the nitration temperature of 95 °C [31] Molecules 2021, 26, 4209 2 of 9…”

“…BN aromatics have been widely investigated in recent years since the materials possess attractive physical and chemical properties and hold potential applications in the light-emitting polymer [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 ], semiconductor [ 13 , 14 , 15 , 16 , 17 ], and other research fields [ 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 ]; however, there have been relatively few reports on the synthesis of nitrated BN aromatics. Thus far, only five mononitro-BN aromatics have been reported [ 30 , 31 ].…”