“Texas-Sized” Molecular Boxes: From Chemistry to Applications

Abstract

The design and synthesis of novel macrocyclic host molecules continues to attract attention because such species play important roles in supramolecular chemistry. However, the discovery of new classes of macrocycles presents a considerable challenge due to the need to embody by design effective molecular recognition features, as well as ideally the development of synthetic routes that permit further functionalization. In 2010, we reported a new class of macrocyclic hosts: a set of tetracationic imidazolium macrocycles, which we termed “Texas-sized” molecular boxes (TxSBs) in homage to Stoddart’s classic “blue box” (CBPQT4+). Compared with the rigid blue box, the first generation TxSB displayed considerably greater conformational flexibility and a relatively large central cavity, making it a good host for a variety of electron-rich guests. In this review, we provide a comprehensive summary of TxSB chemistry, detailing our recent progress in the area of anion-responsive supramolecular self-assembly and applications of the underlying chemistry to water purification, information storage, and controlled drug release. Our objective is to provide not only a review of the fundamental findings, but also to outline future research directions where TxSBs and their constructs may have a role to play.

Pb2+-Containing Metal-Organic Rotaxane Frameworks (MORFs)

“…To date, crown ether [13][14][15][16][17][18], "blue box" (CBPQT 4+ ) [19,20], cucurbiurils [21][22][23], octametallic metallacrown [24][25][26][27], and polyamide [28,29] have been utilized to produce a series of MORF structures. The Texas-sized molecular box ([cyclo [2](2,6-di(1Himidazol-1-yl)pyridine) [2](1,4-dimethylenebenzene), 1 4+ ) [30,31] was developed to construct MORFs cooperating with metal cations (e.g., Zn 2+ , Ag + , or lanthanide) and aromatic dicarboxylate anions (Figure 1).…”

Giant N-heterocyclic carbene-containing macrocycles for cobalt-catalysed hydroboration of alkynes

“…The fundamental aspects as well as versatile applications of the TxSB family in supramolecular and materials chemistry have been well documented in a recent review. 13 Intrigued by the fascinating chemistry TxSBs displayed, 14 we were interested in investigating whether larger macrocycles could be synthesized utilizing methods similar to that used for TxSB synthesis. Typically, the synthesis of TxSBs involves an effective four-component cyclization of 2,6-bis(1H-imidazol-1-yl)pyridine (1, Scheme 1) with various bis-(bromomethyl)-substituted arenes.…”

“…Although several different linking spacers to bridge molecule 1 have been explored following the observation of TxSB 2a by the Sessler and Gong groups, 13 to our surprise, no examples attempting to replace the key linker molecule 1 have been reported in nearly a decade since the first publication of TxSBs.…”

“…15 The NHC-ligating properties are overlooked for TxSBs, although their applications in supramolecular and materials chemistry have been explored. 13 Among known metal-NHC catalysts, Co-NHC complexes have attracted great attention as they displayed remarkable potential in (transfer) hydrogenation, 16 hydrosilylation 17 and many cross-coupling reactions. 15 However, NHC complexes of cobalt were rarely studied for hydroboration catalysis of alkenes that provide valuable boronate esters as key precursors for C-C coupling reactions, 18 and to the best of our knowledge they are unknown for alkyne hydroboration, while other cobalt catalysts have been reported for this reaction.…”

“…Compared to the 58% isolated yield for 2a reported in the literature, the relatively low yield for 2b could be attributed to the larger steric hindrance of the linking agent. 2b was characterized by FT-IR, 1 H and 13 C NMR and highresolution mass spectra (HR-MS). HR-MS of 2b displayed peak envelops at m/z 1289.2031 and 1121.2511, corresponding to species [M + Na] + and [M À PF 6 ] + , respectively, which matched with those calculated.…”