A theoretical study of the neutral and the double-charged cation of cyclo[8]pyrrole and its interaction with inorganic anions

Abstract

A theoretical study of the neutral and the double-charged cation of cyclo [8]

Cyclo[8]isoindoles: Ring‐Expanded and Annelated Porphyrinoids

“…In recent years there has been a growing focus on the chemistry of ring-expanded porphyrins such as hexaphyrins and octaphyrins, because their properties differ markedly from those of conventional porphyrins in a manner that makes them potentially suitable for a number of novel practical applications. [1][2][3][4][5] Cyclo [8]pyrrole ([30]octaphyrin(0.0.0.0.0.0.0.0)), along with its smaller cyclo [6]-and cyclo [7]pyrrole analogues, was first reported by Sessler and co-workers based on an oxidative coupling of 2,2'-bipyrrole with FeCl 3 . [6] A key structural difference with respect to the porphyrins is the complete absence of meso carbon atoms.…”

“…[7] The photophysical, [5] anion-binding, [7a,b] and liquid-crystalline properties [7c] of cyclo[n]pyrroles (n = 6-8) have been studied in-depth, along with their electronic structures. [7d, 8] The UV/ Vis absorption spectra of cyclo [8]pyrroles contain a weaker band at approximately 430 nm (e % 1 10 5 m À1 cm À1 ) and a more intense band at approximately 1100 nm (e % 2 10 5 m À1 cm À1 ). [6a] The strong absorbance in the near-IR (NIR) region makes these compounds potentially suitable for use in optical storage and signaling devices.…”

“…[6,7] The ability to fine-tune the wavelengths of the major absorption bands based on structural modifications such as ring annelation would greatly enhance the utility of these compounds for practical applications. Herein, we report the first successful synthesis of cyclo [8]isoindole (3) based on an oxidative coupling of bicyclo[2.2.2]octadiene(BCOD)fused 2,2'-bipyrrole (1), followed by the retro-Diels-Alder reaction of cyclo [8]BCODpyrrole (2; Scheme 1). We also report an in-depth analysis of the optical properties and electronic structures of 2 and 3 based on magnetic circular dichroism (MCD) spectroscopy and time-dependent (TD) DFT calculations.…”

“…When the reaction was carried out using the nitrosonium ion (generated from NaNO 2 with acid) as a mild oxidant in 1m H 2 SO 4 and concentrated H 2 SO 4 solutions, lower yields of 24 and 40 %, respectively, were obtained (Table 1, entries 2 and 3). When acetic acid was used instead as part of an attempt to synthesize a free-base cyclo [8]BCODpyrrole, surprisingly, X-ray crystallography revealed that 2 was still obtained in 21 % yield after recrystallization from MeOH/CHCl 3 (Figure 1). [12] The sulfate ion was probably derived from the Na 2 SO 4 used to dry the organic layer as part of the extraction process (entry 4).…”

“…[12] The sulfate ion was probably derived from the Na 2 SO 4 used to dry the organic layer as part of the extraction process (entry 4). Cyclo [8]pyrroles have been reported previously to exhibit strong anion-binding properties. [7a-b] Since the SO 4 2À ion may be acting as a template for cyclization, Na 2 SO 4 was added to the initial reaction mixture (entries 5-7).…”