Theoretical investigation of nitrogen disubstituted corannulenes

The effect of nitrogen substitution on corannulene has been investigated employing the PBE density functional and the 6-31G* basis set. We have replaced two carbon atoms by 2 nitrogen atoms. Among the 22 isomers investigated we have found that the most stable C18N2H20 isomer, 1 has two nitrogen atoms on the same six membered ring, in para positions. One of the nitrogen atoms in located at the rim of corannulene and the other is at the hub of corannulene. The later result is in excellent agreement with the predicted stability of C58N2 heterofullerenes. Thus, it seems that there is a clear correlation between the stability of substituted heterofullerenes and heterobuckybowls. The triplet state of isomer 1 is 18 kcal/mol less stable than the singlet state. The second most stable isomer, 2, also have one nitrogen at the rim and another at the hub, it less stable than isomer 1 by 6.2 kcal/mol. However, isomers 2-5 are extremely close in energetic terms. The IR spectra of the most stable isomers, NMR chemical shifts and NICS have been determined. The results indicate that the aromaticity of isomer 1 diminished from that observed in corannulene. Isomer 1 has small aromatic character in the central pentagon and two hexagons; the antiaromatic character is seen for the remaining 3 hexagons. The later results are in contrast with the observed for corannulene, which has aromatic character in the hexagons and antiaromatic on the pentagon. The HOMO-LUMO gap of isomer 1 is 1.23 eV, suggesting reasonable kinetic stability, although it is more than a 50% smaller than that of corannulene 3.03 eV. As by product we have investigated the properties of 1,2-diazacorannulene, a parent compound of 1,2-diazadibenzo[d,m]corannulene whose synthesis was not reached in a recent work.