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Xianfeng Shen

Publications and source records attributed to Xianfeng Shen.

5 recordsLinked to original sources
PubMed2005

Polyphenyl macrocyclic oligophenylenes.

The Diels-Alder reaction of tribenzohexadehydro[12]annulene (12) and 3,4-diphenyl-2,5-dimethylcyclopentadienone (13) at 300 degrees C gave the triple adduct 2,3,10,11,18,19-hexaphenyl-1,4,9,12,17,20-hexamethylhexa-o-phenylene (6b) in 13% yield. NMR and X-ray analysis indicated that 6b adopts a screw conformation (C2) rather than a crown conformation (C3), and computational studies seem to rule out any interconversion of the two. Palladium-catalyzed coupling of 1,2-bis(4-bromophenyl)-3,4,5,6-tetraphenylbenzene (17) and the corresponding bis(boronic acid) 18 gave a mixture of linear and cyclic oligomers of hexaphenylbenzene containing two to six hexaphenylbenzene subunits. A macrocyclic tetramer was isolated from this mixture in 5% yield, and X-ray analysis showed it to be the "supertetraphenylene" 7 (C168H112) that contains a large central cavity and packs to form highly solvated, porous crystals. The difficulties encountered in the purification of 7 led to the development of alternative, more highly selective syntheses that give the pure macrocycle more easily but in essentially the same overall yield.

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PubMed2004

Synthesis of polyphenylene dendrimers related to "cubic graphite".

Four large, 6-fold symmetric, polyphenylene hydrocarbons have been prepared by short syntheses that chiefly employed alkyne trimerization, palladium-catalyzed coupling, and Diels-Alder reactions. The two largest of these molecules, hexakis[4'-(pentaphenylphenyl)biphenyl-4-yl]benzene (4, C(294)H(198)) and hexakis[4'-(2,3,4,5-tetraphenylphenyl)biphenyl-4-yl]benzene (5, C(258)H(174)) are substructures of "phenylogous cubic graphite", and the other two, hexakis(2',3',4',5',6'-pentaphenylbiphenyl-4-yl)benzene (26, C(258)H(174)) and hexakis(2',3',4',5'-tetraphenylbiphenyl-4-yl)benzene (25, C(222)H(150)) are strongly pitched, six-bladed molecular propellers. The X-ray crystal structure of compound 26 has also been determined; dendrimer 26 is at present the largest crystallographically characterized hydrocarbon.

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PubMed2003

Synthesis and structure of a polyphenylene macrocycle related to "cubic graphite".

[structure: see text] Palladium-catalyzed coupling of 1,2-bis(4-bromophenyl)-3,4,5,6-tetraphenylbenzene and the corresponding hexaphenylbenzene bis(boronic acid) gave a mixture of linear and cyclic oligomers of hexaphenylbenzene. An X-ray crystal structure of the tetrameric oligomer showed it to be the polyphenylene macrocycle 4 (C(168)H(112)). The roughly D(2) symmetric macrocycle contains a large central cavity, and it is one of the channel substructures of "phenylogous cubic graphite".

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PubMed2002

Octaphenylbiphenylene and dodecaphenyltriptycene.

Octaphenylbiphenylene, the expected dimer of tetraphenylbenzyne, has been prepared in low yield by diazotization of 3,4,5,6-tetraphenylanthranilic acid, and its X-ray structure has been determined. The X-ray structure of a second, abnormal dimer of tetraphenylbenzyne, 1,2,3,8,9,10-hexaphenyldibenzo[fg,op]naphthacene has also been determined; this is a saddle-shaped polycyclic aromatic hydrocarbon. 1,2,3,4,5,6,7,8,13,14,15,16-Dodecaphenyltriptycene, perhaps the most crowded triptycene derivative yet prepared, has been made by the reaction of tetraphenylbenzyne with 1,2,3,4,5,6,7,8-octaphenylanthracene, which in turn was synthesized in two steps from commercial starting materials. The X-ray structure of the dodecaphenyltriptycene nonabenzene solvate is a remarkable channel containing structure in which more than 50% of the unit cell volume is occupied by the benzene molecules.

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