o-(2-Thienyl)vinylarene as an Alternative Synthetic Motif for Porphyrinoids: o-Arene-Connected Porphyrinoids

Abstract

o-Arene-connected porphyrinoids were synthesized with o-(2-thienyl)vinylarene motif as a new building block for porphyrinoids. This motif can replace meso-aryl-substituted dipyrromethene and serve as a command key arranging o-connectivity of porphyrinoid. While 6a (benzene version) is very weak, 6b (pyridine version) shows a substantial amount of diatropic ring current due to reduced steric hindrance (without H23) and rigidified Pd-6a became more aromatic than 6b.

Fundamental difference between simple arenes and PAHs found in o-PAH-connected porphyrins

“…S8 in ESI †). 6 The ring current properties can be explained by the X-ray structures of 3a and 4a, although more conformers and tautomers are expected based on the X-ray structures of 3a, Pd-3a, and 4a (Fig. S7-12 in ESI †).…”

“…S6 in ESI †). 6 This might be possible because of the expected low rotation barrier. 24 The rotation barrier between 3a 1 and 3a 5 was calculated to be 6.9 kcal mol −1 .…”

“…Thus, the X-ray structures of 3a and Pd-3a suggest vinyl rotation, although 3a is a quasi-plane with the thiophene and vinyl moieties angled (20.8° and 35.0°) to the mean plane. 6 Furthermore, the solid state of 4a indicates the presence of thiophene rotation and NH tautomers. Based on their crystal structures, four distinct conformers (inner/outer H 17 and planar/perpendicular thiophene) and their respective NH tautomers were inferred to exist at equilibrium.…”

“…Recently, our group reported o -benzene (or pyridine)-connected porphyrinoids with o -(2-thienyl)vinylarene motifs as new building blocks for o -connected porphyrinoids. 6 This motif can replace meso -aryl-substituted dipyrromethenes and serve as a command key for arranging the o -connectivity of the porphyrinoids. Some aromatic o -connected porphyrinoids are unstable without protonation, 7 and unsubstituted vinyl groups are rare and limited to meso -benzoporphycenes.…”

Organometallic Chemistry within the Structured Environment Provided by the Macrocyclic Cores of Carbaporphyrins and Related Systems

“…A related, more flexible, system 392 called allyliporphyrin has been prepared and this also gave excellent yields of the corresponding palladium(II) complex 393 ( Scheme 63 ) [ 231 ]. Porphyrinoids 394 with intermediary structures between 384 and 392 have been described [ 232 ]. As is the case for 392 , benzo-fused allyliporphyrin 394a is in equilibrium with alternative conformations, or tautomers, in particular the alternative aromatic species 394a′ .…”