B^III 5‐Arylsubporphyrins and B^III Subporphine

Abstract

Boron(III) 5-arylsubporphyrins and B subporphine are promising precursors for functional B subporphyrins bearing asymmetric meso-substituents. Herein, we report the first synthesis of these molecules. Among many aryl acid chlorides examined, 4-nitrobenzoyl chloride gave B 5-(4-nitrophenyl)subporphyrin in 10 % yield in condensation with triethylamine-tri-N-tripyrromethene-borane. The nitro group of this B subporphyrin was reduced with NaBH to prepare B 5-(aminophenyl)subporphyrin, which was converted into B 5-phenylsubporphyrin via the corresponding diazonium salt. B subporphine was synthesized by condensation of triethyl orthoformate with triethylamine-tri-N-tripyrromethene-borane. Progressive removal of meso-phenyl substituents leads to continuous changes in the optical properties, whereas the B subporphine deviates from this trend in some properties.

Recent advances in subphthalocyanines and related subporphyrinoids

“…The other example of meso -free A 3 SubP 415 has been prepared from the f type tripyrrane 413 , by reaction with triethylamine borane, to afford the corresponding tri- N -tripyrromethene complex 414 , which is in situ condensed with boiling triethyl orthoformate (Scheme 39). 595…”

“…105). 595 The latter characterizes the degree of curvature of SubPs, which is defined by the distance from the mean plane of the peripheral six β-pyrrolic carbons to the central boron atom. Compared to SubPzs (1.76 Å bowl-depth) and SubPcs (2.55 Å bowl-depth), 76 the conical structure of SubPs is considerably shallower.…”

“…Thus, SubPs 606 , 430 and 390 (Table 25) exhibit their corresponding B-bands at 352, 362 and 373 nm, respectively, while the Q-bands appear at, 440 and 461, 450 and 461, and 484 nm, respectively, indicating electronic interaction of the meso -phenyl groups with the SubP core. The latter has been attributed to smaller steric hindrance around the meso -phenyl groups in SubPs related to the corresponding tetraphenylporphyrins, 595 which leads to a substantial electronic conjugation of the aromatic meso -rings to the SubP core in meso -phenyl and thienyl-SubPs 390 and 421 , contrasting with porphyrins, for which this conjugation is only marginal.…”

“…Upon sequential addition of meso -phenyl rings the fluorescence spectra show red-shift, with the fluorescence bands mirroring the respective Q-like bands, and Stokes shifts gradually higher of 150, 550, 780, and 880 cm −1 , respectively. 595 When going from 415 to 390 the fluorescence quantum yields ( ϕ F ) decrease, while the fluorescence lifetimes ( τ F ) become elongated in the order 415 = 390 < 606 < 430 .…”

Singly and Doubly Quinoxaline‐Fused BIII Subporphyrins

“…Since the first synthesis in 2006, the chemistry of subporphyrins has been extensively studied, showing their unique properties and reactivities. Different from meso ‐aryl‐substituted porphyrins, most of meso ‐aryl substituents in subporphyrins can rotate rather freely, hence causing large substituent effects on the optical and electronic properties . Taking advantage of this feature, many interesting examples have been explored.…”