Meso-alkylidenyl-thia(p-benzi)porphyrins and their unusual protonation selectivity

Abstract

Meso-alkylidenyl-thia(p-benzi)porphyrin and its ring expanded analog containing exocyclic C-C double bonds at meso-positions, undergo initial protonation at the exocyclic alkylidene alpha-carbon.

Expanded Porphyrins: Intriguing Structures, Electronic Properties, and Reactivities

“…Two major conformations have been identified, namely a rectangular conformation (Figure 6 a) and a dumbbell-shaped conformation (Figure 6 b). Through extensive studies, it has been recognized that most meso-aryl [26]hexaphyrins adopt rectangular conformations, in which two pyrrole rings in the long central side are inverted, while the remaining four pyrrole rings point inwards to adjoin the effective intramolecular hydrogen bonding. This structure is almost planar, which allows its strong 26p aromaticity, although the planarity is lower than that of porphyrins because of the steric hindrance between the inner b protons at the inverted pyrrole rings.…”

“…In 1999, Cavaleiro and co-workers reported an important example of the isolation and characterization of meso-arylsubstituted [26]hexaphyrin 3 and [28]hexaphyrin 37. [36] We subsequently reported the facile one-pot synthesis of the series of meso-aryl-substituted expanded porphyrins, including 3.…”

“…In this nomenclature, an name of an expanded porphyrin consists of three parts: 1) a core name that indicates the number of pyrrole subunits in such a way as to use pentaphyrin 2, hexaphyrin 3, and heptaphyrin 4 for expanded porphyrins consisting of five, six, and seven pyrrolic subunits, respectively, 2) the number in the square-bracketed prefix indicates the number of p electrons in the effective macrocyclic conjugation, and 3) the numbers in the roundbracketed suffix indicate the numbers of bridging carbon atoms between the constitutional pyrrole groups, starting from the largest unit. According to this nomenclature, porphyrin 1 and hexaphyrin 3 are named as [18]porphyrin-(1.1.1.1) and [26]hexaphyrin(1.1.1.1.1.1), respectively. In this Review, some expanded porphyrins are named after their colors, which include sapphyrin for [22]pentaphyrin(1.1.1.1.0) 5, amethyrin for [24]hexaphyrin(1.0.0.1.0.0) 6, [10] and rubyrin for [26]hexaphyrin(1.1.0.1.1.0) 7 (Figure 2).…”

“…According to this nomenclature, porphyrin 1 and hexaphyrin 3 are named as [18]porphyrin-(1.1.1.1) and [26]hexaphyrin(1.1.1.1.1.1), respectively. In this Review, some expanded porphyrins are named after their colors, which include sapphyrin for [22]pentaphyrin(1.1.1.1.0) 5, amethyrin for [24]hexaphyrin(1.0.0.1.0.0) 6, [10] and rubyrin for [26]hexaphyrin(1.1.0.1.1.0) 7 (Figure 2). [11] …”

“…[26] Another important category is carbaporphyrinoids, in which one or more of pyrrole rings are replaced by carbocyclic units [25d, 27] or N-confused pyrroles.…”