Sub--benziporphyrin: a subcarbaporphyrinoid and its B complex with an unprecedented planar tridentate 14π-aromatic network.

Sub--benziporphyrins were synthesized by Pd-catalyzed cross-coupling of ,'-diboryl--benzitripyrrane with 9,10-bis(1,1-dibromomethylenyl)anthracene. Reaction of sub--benziporphyrin with PhBCl and triethylamine gave its B-phenyl complex as a tetracoordinate nonaromatic B complex. In contrast, the reaction with BBr and triethylamine furnished a neutral B porphyrinoid with a planar and triangular coordination as the first example, in which the -phenylene unit was partially reduced, allowing for the global 14π-aromatic circuit. This aromatic B complex is stable and inert towards nucleophiles such as pyridine, 4-dimethylaminopyridine, and fluoride anions but undergoes an oxygen-insertion reaction upon refluxing in the air. In addition, this B complex displays structured vibronic Q-bands, slow S-state decay, and fluorescence ( = 0.30 and = 9.7 ns), in line with its aromatic nature, while the nonaromatic B complexes show ill-defined absorption spectra and very fast S-state decays.