Shape‐Persistent Phenylene‐Acetylene Macrocycles: Large Rings — Low Yield?

Hoeger, Sigurd

doi:10.1002/chin.200538262

Cited by 3 publications

(6 citation statements)

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“…62,65,66 The observation that the shift is most pronounced between the pentagon and the hexagon possibly reflects effects of ring strain, which should especially affect the square and the heptagon. Note that the heptagon [35]-HC shows a maximum at higher voltage than [30]-HC.…”

Section: Resultsmentioning

confidence: 98%

“…Strained Macrocycles. Besides the regular hexagonal honeycombenes, the DMQP precursor (but not the smaller DMTP precursor) occasionally also forms strained rings with square "[20]-HC", pentagonal " [25]-HC", or heptagonal symmetry " [35]-HC", as shown in Figure 5. The strain-induced deformation of the planar rings can be seen in the STM images: The square cycloicosaphenylene (20 phenyl rings) in Figure 5b, formed by reaction of four DMQP molecules, shows a convex deformation of its edges; that is, they are curved toward the outside.…”

Section: Resultsmentioning

confidence: 99%

“…However, for the gas-phase molecules, a similarly flat molecular geometry cannot be expected, because even in the simple biphenyl molecule the two phenyl rings are twisted in the minimumenergy conformation, such that the molecule adopts a nonplanar conformation. 73 Indeed, geometry optimizations for the isolated [n]-HC molecules (n = 20,25,30,35) in a perfectly planar conformation with the D mh (m = n/5) symmetry constraint lead to structures that are not local minima on the respective energy surfaces. Rather, calculation of the geometric Hessian shows that a total number of 20, 20, 27, and 32 imaginary frequencies are obtained for n = 20, 25, 30, and 35, respectively, the eigenvectors of which describe both twisting coordinates of adjacent phenyl rings and global out-ofplane deformations that break the D mh symmetry of the molecule.…”

Section: Resultsmentioning

confidence: 99%

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On-Surface Synthesis and Characterization of Honeycombene Oligophenylene Macrocycles

Chen

Shang²,

Wang³

et al. 2016

ACS Nano

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We report the on-surface formation and characterization of [30]-honeycombene, a cyclotriacontaphenylene, which consists of 30 phenyl rings (CH) and has a diameter of 4.0 nm. This shape-persistent, conjugated, and unsubstituted hexagonal hydrocarbon macrocycle was obtained by solvent-free synthesis on a silver (111) single-crystal surface, making solubility-enhancing alkyl side groups unnecessary. Side products include strained macrocycles with square, pentagonal, and heptagonal shape. The molecules were characterized by scanning tunneling microscopy and density functional theory (DFT) calculations. On the Ag(111) surface, the macrocycles act as molecular quantum corrals and lead to the confinement of surface-state electrons inside the central cavity. The energy of the confined surface state correlates with the size of the macrocycle and is well described by a particle-in-the-box model. Tunneling spectroscopy suggests conjugation within the planar rings and reveals influences of self-assembly on the electronic structure. While the adsorbed molecules appear to be approximately planar, the free molecules have nonplanar conformation, according to DFT.

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Section: Resultsmentioning

confidence: 98%

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

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On-Surface Synthesis and Characterization of Honeycombene Oligophenylene Macrocycles

Chen

Shang²,

Wang³

et al. 2016

ACS Nano

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“…110 The same macrocyclic structural motif incorporating tert-butyl groups 56b can be, however, obtained in much higher yields (75% yield) by the cyclization of the 6-mer open-chain precursor 57 or 58 under pseudo-high-dilution conditions (tertbutyl groups were necessary to achieve the necessary solubility of the products). 111,112 An important drawback of the second approach was the need for several synthetic steps for preparing the open-chain precursors, each one involving protection and deprotection stages. However, one important advantage of the sequential synthesis is the possibility of synthesizing the much larger macrocycles 56b or 59 through the proper selection of the structural components (Figure 17) as reported by Moore and coworkers.…”

Section: Experimental Aspects In the Synthesis Of Macrocyclesmentioning

confidence: 99%

Macrocyclization Reactions: The Importance of Conformational, Configurational, and Template-Induced Preorganization

et al. 2015

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“…To improve the efficiency of macrocyclization reactions, many strategies such as noncovalent or covalent templation, intramolecular ring closure, and dynamic covalent bond formation, have been proposed and probed with various successes and limitations. 40,41 The one-step reaction shown in Scheme 1 raises interesting mechanistic questions. The efficient formation of 19 was rationalized by the preorganization of uncyclized precursors that fold into a crescent conformation.…”

Section: Folding-assisted Macrocyclizationmentioning

confidence: 99%

Hollow Crescents, Helices, and Macrocycles from Enforced Folding and Folding-Assisted Macrocyclization

2008

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This Account reviews the progress made by us on creating porous molecular crescents, helices, and macrocycles based on aromatic oligoamides. Inspired by natural pore- or cavity-containing secondary structures, work described in this Account stemmed from the development of foldamers consisting of benzene rings linked by secondary amide groups. Highly stable, three-center intramolecular hydrogen bonds involving the amide linkages are incorporated into these aromatic oligoamides, which, along with meta-linked benzene units that introduce curvatures into the corresponding backbones, leads to tape-like, curved backbones. Depending on their chain lengths, aromatic oligoamides that fold into crescent and helical conformations have been obtained. Combining results from modeling and experimentally measured data indicates that the folding of these oligomers is readily predictable, determined by the localized intramolecular three-center H-bonds and is independent of side-chain substitution. As a result, a variety of reliably folded, modifiable scaffolds can now be constructed. The well-defined crescent or helical conformations contain noncollapsible internal cavities having multiple introverted amide oxygen atoms. Changing the backbone curvature by tuning the ratio of meta- to para-linked benzene units leads to crescents or helices with cavities of tunable sizes. For example, oligoamides consisting of meta-linked units contain cavities of approximately 9 A across, while those with alternating meta- and para-linked units have cavities of over 30 A across. The generality of such a folding and cavity-creating strategy has also been demonstrated by the enforced folding of other types of aromatic oligomers such as oligo(phenylene ethynylene)s, aromatic oligoureas, and aromatic oligosulfonamides. More recently, the folding of aromatic oligoamides was found to assist efficient macrocyclization reactions, which has provided a convenient method for preparing a new class of large shape-persistent macrocycles in high yields. The folded and cyclic structures were extensively characterized based on multiple techniques such as one- and two-dimensional NMR, mass spectrometry, and X-ray crystallography, as well as theoretical calculations. The enforced folding and folding-assisted cyclization of oligomers have provided a predictable strategy for developing crescent, helical, and cyclic structures containing nanosized voids that are mostly associated with the tertiary and quaternary structures of proteins. The availability of these porous molecules has supplied a new class of nanosized building blocks that provide both opportunities and challenges for creating the next-generation nanostructures capable of presenting multiple introverted functional groups, forming various pores and channels, and finally, developing protein-like pockets.

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Shape‐Persistent Phenylene‐Acetylene Macrocycles: Large Rings — Low Yield?

Abstract: For Abstract see ChemInform Abstract in Full Text.

Cited by 3 publications

References 1 publication

On-Surface Synthesis and Characterization of Honeycombene Oligophenylene Macrocycles

On-Surface Synthesis and Characterization of Honeycombene Oligophenylene Macrocycles

Macrocyclization Reactions: The Importance of Conformational, Configurational, and Template-Induced Preorganization

Hollow Crescents, Helices, and Macrocycles from Enforced Folding and Folding-Assisted Macrocyclization

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