Oligopyrrolic Cages: From Classic Molecular Constructs to Chemically Responsive Polytopic Receptors

Abstract

Conspectus “Functional molecular systems”, discrete and self-assembled constructs where control over molecular recognition, structure, bonding, transport, release, catalytic activity, etc., is readily achieved, are a topic of current interest. Within this broad paradigm, oligopyrrolic cages have garnered attention due to their responsive recognition features. Due to the presence of slightly polar pyrrole subunits which can also behave as hydrogen-bonding donors, these oligopyrrolic cages are potential receptors for various polarized species. In this Account, we summarize recent advances involving the syntheses and study of (1) covalent oligopyrrolic macrobicyclic cages, (2) oligopyrrolic metallacages, and (3) oligopyrrolic noncovalently linked cages. Considered in concert, these molecular constructs have allowed advances in applied supramolecular chemistry; to date, they have been exploited for selective guest encapsulation studies, anion binding and ion-channel formation, and gas absorption, among other applications. While key findings from others will be noted, in this Account will focus on our own contributions to the chemistry of discrete oligopyrrolic macrocycles and their use in supramolecular host–guest chemistry and sensing applications. In terms of specifics, we will detail how oligopyrrole cages with well-defined molecular geometries permit reversible guest binding under ambient conditions and how the incorporation of pyrrole subunits within larger superstructures allows effective control over anion/conjugate acid binding activity under ambient conditions. We will also provide examples that show how derivatization of these rudimentary macrocyclic cores with various sterically congested β-substituted oligopyrroles can provide entry into more complex supramolecular architectures. In addition, we will detail how hybrid systems that include heterocycles other than pyrrole, such as pyridine and naphthyridine, can be used to create self-assembled materials that show promise as gas-absorbing materials and colorimetric reversible sensors. Studies involving oligopyrrolic polymetallic cages and oligopyrrolic supramolecular cages will also be reviewed. First, we will discuss all-carbon-linked oligopyrrolic bicycles and continue on to present systems linked via amines and imines linkages. Finally, we will summarize recent work on pyrrolic cages created through the use of metal centers or various noncovalent interactions. We hope that this Account will provide researchers with an initial foundation for understanding oligopyrrolic cage chemistry, thereby allowing for further advances in the area. It is expected that the fundamental design and recognition principles made in the area of oligopyrrole cages, as exemplified by our contributions, will be of general use to researchers targeting the design of functional molecular systems. As such, we have structured this Account so as to summarize the past while setting the stage for the future.

TEtraQuinolines (TEQs): A missing link in the family of porphyrinoid macrocycles

“…Indeed, (+)-8a and (-)-8a displayed mirror-image CPL spectra in the presence of 4 eq of TFA or 1 eq of ZnCl2 with absolute luminescence dissymmetry factors (|glum|) of 5.61 x 10 -4 and 3.16 x 10 -4 , respectively (Supplementary Figs. [15][16][17][18].…”

Recent developments in calix[4]pyrrole (C4P)-based supramolecular functional systems

“…Considering the involvement of numerous natural receptors in regulating the intricate phenomena in nature through noncovalent interactions, the science of supramolecular chemistry took birth, imitating the basic design and functions of natural receptors for the construction of artificial functional receptors realizing particular goals. [1][2][3][4][5][6][7][8] Among the numerous supramolecular receptors, 9,10 the non-aromatic tetrapyrrolic synthetic macrocyclic receptor (C4P) has emerged as significant receptor and ligand for diverse purposes owing to its structural variety, easy one-pot synthesis, and recognition ability towards anions, ion-pairs, neutral molecules, and metal ions of fundamental importance. [11][12][13][14][15][16][17][18][19][20][21][22][23] Adolf von Baeyer (1835-1917, a German Chemist, Noble Prize in Chemistry, 1905) is credited for the discovery of the parent C4P in 1886 through the acid-mediated condensation of pyrrole with acetone in a single step (Fig.…”

Pyrrole‐Based Cryptand‐Like Cages: A Critical Overview of Synthetic Strategies and Applications

“…[10] Very recently, during preparation of this manuscript, an account has been published describing oligopyrrolic cages. [11] Laterally non symmetrical azaand oxa-cryptands have also been reviewed explaining their synthesis and usage in catalysis. [12] But cryptands containing a particular framework that is pyrrole has not been systematically reviewed.…”

“…Most of those review articles focused on the complexation between cryptand‐based hosts and anions/metal ions/organic guests [10] . Very recently, during preparation of this manuscript, an account has been published describing oligopyrrolic cages [11] . Laterally non symmetrical aza‐ and oxa‐cryptands have also been reviewed explaining their synthesis and usage in catalysis [12] .…”