Sub-m-benziporphyrin: A Subcarbaporphyrinoid and Its BIII Complex with An Unprecedented Planar Tridentate 14-Aromatic Network

Abstract

Sub-m-benziporphyrins were synthesized by Pd-catalyzed cross-coupling of α,α’-diboryl-m-benzitripyrrane with 9,10-bis(1,1-dibromomethylenyl)anthracene. Reaction of sub-m-benziporphyrin with PhBCl2 and triethylamine gave its B-phenyl complex as a tetracoordinate nonaromatic BIII complex. In contrast, the reaction with BBr3 and triethylamine furnished a neutral BIII porphyrinoid with a planar and triangular coordination as the first example, in which the m-phenylene unit was partially reduced, allowing for the global 14-aromatic circuit. This aromatic BIII complex is stable and inert towards nucleophiles such as pyridine, 4-dimethylaminopyridine, and fluoride anion but undergoes an oxygen-insertion reaction upon refluxing in the air. In addition, this BIII complex displays structured vibronic Q-bands, slow S1-state decay, and fluorescence (F = 0.30 and F = 9.7 ns), in line with its aromatic nature, while the nonaromatic BIII complexes show ill-defined absorption spectra and very fast S1-state decays.