Shape-Persistent Macrocycles: Structures and Synthetic Approaches from Arylene and Ethynylene Building Blocks
ABSTRACT Shape-persistent arylene ethynylene macrocycles have attracted much attention in supramolecular chemistry and materials science because of their unique structures and novel properties. In this Review we describe recent examples of macrocycle synthesis by cross-coupling (Sonogashira: aryl acetylene macrocycle or Glaser: aryl diacetylene macrocycle) and dynamic covalent chemistry. The primary disadvantage of the coupling methods is the kinetically determined product distribution, since a significant portion of oligomers grow beyond the length of the cyclic targets ("overshooting"). Better results have been obtained recently by a dynamic covalent approach involving reversible metathesis reactions that afford macrocycles in one step. Mechanistic studies demonstrate that macrocycle formation is thermodynamically controlled by this route. Remaining synthetic challenges include the efficient preparation of site-specifically functionalized structures and larger, more complex two- and three-dimensional molecules.
- SourceAvailable from: mq.edu.au[Show abstract] [Hide abstract]
ABSTRACT: The use of laser polarimetry detection coupled with HPLC is demonstrated to enable the discovery of enantioselective receptors from racemic dynamic combinatorial libraries. Templating with an enantiopure analyte, such as (-)-adenosine, leads to amplification of one enantiomer of the cyclic dimer. A result confirmed with a pseudo-racemic library wherein one of the enantiomers was d-labeled for mass spec analysis. The resulting dimer is thus an enantioselective receptor for (-)-adenosine.Journal of the American Chemical Society 10/2006; 128(38):12422-3. DOI:10.1021/ja0647699
- [Show abstract] [Hide abstract]
ABSTRACT: The monomeric complex [Pd(dmba)Cl(PTA)] [dmba = N,C-chelating 2-(dimethylaminomethyl)phenyl; PTA = 1,3,5-triaza-7-phosphaadamantane] has been obtained and its crystal structure has been established by X-ray diffraction. Conditions for an efficient copper- and amine-free catalyzed Sonogashira reaction of aryl bromides and chlorides with terminal alkynes by [Pd(dmba)Cl(PTA)] and Pd(OAc)2/PTA have been developed. It is worthwhile noting that a relatively low palladium catalyst loading has been employed.ChemInform 10/2006; 25(24). DOI:10.1021/om060636k
- [Show abstract] [Hide abstract]
ABSTRACT: The geometric and electronic structures of a series of conjugated macrocycles (phenylene-acetylene macrocycles, PAMs) have been studied theoretically with ab initio and semiempirical molecular orbital methods. The ab initio calculations at the HF/6-31G* level demonstrate that the model molecules may have a planar conformation. Bigger macrocycles, for example, 7PAM, 8PAM, and 9PAM, result in several energy minima. The boatlike conformation is the most energetically favored form. Based on the conformational analysis, a novel method for analyzing the ring-strain energy was proposed and used. In view of their potential applications as electronic materials, the electronic structures of a series of PAMs are also investigated. The LUMO-HOMO gaps of the planar PAMs show an odd-even difference behavior. In addition, the HOMOs of the planar species 3PAM, 5PAM, 7PAM, and 9PAM are doubly degenerated.ChemPhysChem 12/2006; 7(12):2593-600. DOI:10.1002/cphc.200600416