Cyclophane

About: Cyclophane is a research topic. Over the lifetime, 2770 publications have been published within this topic receiving 65339 citations. The topic is also known as: cyclophanes.

Imidazolium receptors for the recognition of anions.

Abstract: This tutorial review covers imidazolium receptors for anion recognition according to their topological and structural classification, and includes benzene tripodal, cyclophane and calix-imidazolium, fluorescent imidazolium, ferrocenyl imidazolium, cavitand and calixarene, and polymeric imidazolium systems.

Fluorescent Chemosensors Based on Energy Migration in Conjugated Polymers: The Molecular Wire Approach to Increased Sensitivity

Abstract: We demonstrate herein how conjugated polymers (molecular wires) can be used to interconnect (wire in series) receptors to produce fluorescent chemosensory systems with sensitivity enhancements over single receptor analogues. The enhancement mechanism in the polyreceptor materials is based on an energy migration scheme in which excitations, diffuse along the polymer backbone. Analyte binding produces trapping sites for the excitations which results in greatly attenuated emission intensity. Three different cyclophane-based receptor systems that bind paraquat were investigated. These systems are quenched by paraquat binding, and the quenching enhancements relative to a monomeric model compound were used to determine the efficiency of energy migration. Two polymers with related poly(phenyleneethyny1ene) structures were investigated, and the all-para system was found to exhibit more facile energy migration than the more electronically localized analogue that contained meta linkages. The para polyreceptor system was found to display a 65-fold enhancement in sensitivity to paraquat as compared to a model monoreceptor fluorescent chemosensor. However, we have determined that delocalization alone is not sufficient to produce facile energy migration, and the more delocalized polythiophenes appear to be less effective at energy migration than the para poly(phenyleneethyny1ene) material. Paraquat-induced fluorescent quenching studies on homologous polymers that lacked the cyclophane receptors were also performed. These results indicate that diffusive quenching by paraquat is enhanced by energy migration.

Synthesis of [8]cycloparaphenylene from a square-shaped tetranuclear platinum complex.

Abstract: Hoop-shaped p-conjugated molecules have attracted the attention of theoretical, synthetic, and supramolecular chemists for more than a half century because of their unique structures which have a distorted p system. Among these types of compounds, cycloparaphenylenes have gained much interest recently because of their potential applications in material science; they are the simplest structural unit of armchair carbon nanotubes. Although they have a simple structure, their synthesis has been a significant challenge. Whereas the parent paraphenylenes adopt an extended linear structure, the induced strain resulting from the cyclic and curved structure of cycloparaphenylenes is the major synthetic drawback. Recently, Bertozzi and co-workers have reported the first, and elegant, synthesis of [9]-, [12]-, and [18]cycloparaphenylenes. More recently, Itami and coworkers have reported a selective synthesis of [12]cycloparaphenylene. Both groups utilize the sp-hybridized carbon atom in either cyclohexa-2,5-diene-1,4-diol or cyclohexane-1,4-diol derivatives to induce the curvature, and the diol units are aromatized in the final step. We report herein the synthesis of [8]cycloparaphenylene, which is the smallest cycloparaphenylene synthesized thus far, based on a new synthetic strategy. We envisioned that cis-coordinated, square-shaped tetra(para-substituted oligoaryl)platinum complex 1 could be used as a universal precursor for [4n]cycloparaphenylenes 2 (Scheme 1). Since the bond angles of the cis substituents in platinum complexes are about 908, formation of 1 should not induce significant strain. Indeed, structurally related coordination complexes of palladium and platinum macrocycles containing a 4,4’-bipyridyl unit have been already reported, and their analogues have been widely used in supramolecular chemistry. However, to the best of our knowledge, there is no report involving the synthesis of 1 with only covalent platinum–carbon bonds. If multiple reductive eliminations of platinum from 1 occur, 2 could be formed despite of the increase of molecular strain. We report herein the synthesis of [8]cycloparaphenylene (n = 2) from the corresponding precursor as a proof of principle for this strategy. We calculated the strain energies of several cycloparaphenylenes before attempting the synthesis. On the basis of density functional theory calculations at the B3LYP/6-31G* level of theory, the strain energy of [8]cycloparaphenylene was 74 kcal mol , whereas those of [9]-, [12]-, and [18]cycloparaphenylenes were 69, 50, and 33 kcal mol , respectively. To synthesize [8]cycloparaphenylene (5), 4,4’-bis(trimethylstannyl)biphenyl 3 was first treated with one equivalent of [PtCl2(cod)] (cod = 1,5-cyclooctadiene) in refluxing THF for 35 hours (Scheme 2). The reaction gave the squareshaped platinum complex 4 a in 57% yield, which was treated with 1,1’-bis(diphenylphosphino)ferrocene (dppf) to give 4b in 91% yield. Bromine-induced reductive elimination from 4b at 95 8C for 17 hours in toluene afforded 5 in 49 % yield upon isolation. Addition of iodine or triphenylphosphine, instead of bromide, did not improve the efficiency of the reductive elimination. In the H NMR spectrum of 5, a single peak was observed at d = 7.48 ppm, and in the C NMR spectrum, peaks were observed at d = 137.8 and 127.6 ppm. These spectra are Scheme 1. Synthetic strategy for [4n]cycloparaphenylene.