2,2′-Bipyrrole-Based Porphyrinoids

Abstract

A large number of porphyrinoids containing 2,2'-bipyrrole subunits have appeared since they were originally found as a component of sapphyrin and corrole, and it was found that the bipyrrole subunit endowed macrocycles with specific geometric features and electronic properties. Synthetic methods for bipyrrole-containing precursors for porphyrinoid are summarized in this review; these include coupling reactions of pyrrole rings, pyrrole ring-forming reactions leading directly to bipyrrole units, and synthetic reactions for oligopyrrolic compounds. Some hybrid oligopyrroles having nonpyrrole (hetero)aromatic ring(s) are also included. This review also describes porphyrinoids composed of bipyrrole subunits. Interesting electronic properties derived from strong cyclo-π-conjugation are highlighted in the bipyrrole-based porphyrinoids with or without meso-like carbons. Anion-binding chemistry is one of the main topics for bipyrrole-based macrocycles with less efficient or deficient cyclo-π-conjugation, such as those linked with electronically localized aromatic ring(s), with sp carbon(s), and with amido or imine connection(s). The principal concern in this review is porphyrinoids of relatively large ring size, composed of more than five units of pyrroles and (hetero)aromatic substitutes in total, and so bipyrrole-based porphyrinoids up to five pyrrolic units, such as corroles, porphycenes, sapphyrins, and smaragdyrin, will not be covered here except for some special cases.

Synthesis of Expanded Hetero 2,6‐Pyrihexaphyrins

“…A perusal of literature revealed that Berlin and Breitmaier in 1994 reported the first example of pyridine containing porphyrinoids and ever since several interesting pyridine incorporated porphyrinoids that includes regular,, , , , contracted, expanded, , , and heteroporphyrinoids were reported. Thus, several very stable pyridine and bipyridine, , containing porphyrinoids are reported in recent times and explored their structural, spectral and coordination properties. Recently, we reported synthesis of series m ‐benzihexaphyrins (1.0.0.1.1.1) 1 and studied their properties.…”

Synthesis, Characterization, and Electrochemistry of Open‐Chain Pentapyrroles and Sapphyrins with Highly Electron‐Withdrawing meso‐Tetraaryl Substituents

“…[55][56][57][58][59][60][61] Sapphyrins containing four meso-aryl substituentsc an serve as favorable building blocks fort he further designo fm olecules, which are similar to meso-aryl-substituted porphyrins, whose redox properties and chemicalr eactions can be finely tuned. [15,57,58,60,61] Open-chainp entapyrroles (or pentapyrrotetramethenes) with meso-tetraaryl substituents were first isolated as the majors ide productsi nt he synthesis of corrolew ith ah igh yield (11%,t he same as the target product), [62] and later attracted greater attention as synthetic precursors for the respective sapphyrins. [15,57,58,60,61] Open-chainp entapyrroles (or pentapyrrotetramethenes) with meso-tetraaryl substituents were first isolated as the majors ide productsi nt he synthesis of corrolew ith ah igh yield (11%,t he same as the target product), [62] and later attracted greater attention as synthetic precursors for the respective sapphyrins.…”

Pyrrole N–H anion complexes

“…The synthesis and anion binding properties of a number of these systems were reviewed in a book chapter by Maeda [29]. Aryl-bridged bispyrroles have also been used extensively as building blocks in the construction of macrocycles [11] and for preparing low molecular weight compounds with membrane permeability [58]. A full summary of this work is not possible here.…”

“…In 1996, the non-conjugated tetrapyrrolic macrocycle, calix[4]pyrrole, functioned as a neutral anion receptor (Figure 1) [10]. Expanded porphyrins [11,12], calixpyrroles [13] and their macrocyclic analogues [14,15] have been extensively reviewed in the context of anion and ion pair recognition. In this review we focus on the anion binding properties of neutral and charged acyclic pyrrolic systems.…”