Structure, stability, and aromaticity of M-SubPc (M=B, Al, and Ga): Computational study

A theoretical investigation on the structure, stability, and aromaticity of M-subphthalocyanine (M-SubPc; M 13, Al, and Ga) was performed at the B3LYP/6-31 +G*/ /B3LYP/6-31G* level. The comparison between M-SubPc and the corresponding M-phthalocyanine (M-Pc) was considered. The geometry optimization of the M-SubPc shows that in the Al-SubPc and Ga-SubPc, the steric repulsions among the three azacoupled isoindole moieties increase, as to their macrocycles tend to be far from planarity. The binding energies of Cl-M ... aza-coupled isoindole corrected by the basis set superposition error (BSSE), and the nucleus-independent chemical shift (NICS) values at the ring center, which are a simple and effective local aromaticity probe, were calculated. The results show that Al-SubPc is less stable than both B-SubPc and Al-Pc for larger steric repulsion, smaller binding energy, and weaker aromaticity. In the same way, Ga-SubPc is less stable than both B-SubPc and Ga-Pc. In addition, the ring expansion reactivity occurring in B-SubPc was confirmed by the global aromaticity mirrored by the electrophilicity index omega values. Therefore, the Al-SubPc and Ga-SubPc remain unknown, while the corresponding compounds Al-Pc and Ga-Pc are known experimentally. (c) 2005 Wiley Periodicals, Inc.