Hexabromotricyclobutabenzene and Hexabromohexaradialene: Their Nickel‐Mediated One‐Pot Syntheses and Crystal Structure

Abstract

The reaction of hexakis(dibromomethyl)benzene with [(Bu3 P)2 -Ni(COD)] (COD = 1,5-cyclooctadiene) in DMF at 65-70°C yielded a mixture of the title compounds. The mixture was separated by column chromatography to yield hexabromotricyclobutabenzene (3 a) and hexabromohexaradialene (4) in 24 and 16% yields, respectively. (1) H and (13) C NMR spectroscopy suggest that 3 is obtained as the syn-all-trans isomer 3 a, and the symmetric anti-all-trans isomer 3 b is not obtained at all. The X-ray structures of 3 a and 4 are reported. The hexaradialene 4 has a chair conformation, and deviates from planarity by 43.6°. Heat or radical impurities cause the clean transformation of 3 a to 4.

[6]Radialenes Revisited

“…The structure of the new polymorph of the radialene 14 is, to the best of our knowledge, only the fifth of a simple radialene, the previously determined structures being the first polymorph of 14 [19] and the hexamethyl, [8] hexaethyl, [1b] and hexa-bromomethyl [22] derivatives. All these structures displayed crystallographic inversion symmetry and almost ideal chair conformations, with absolute ring torsion angles of ca.…”

Geometry, Vibration Frequencies, Normal Coordinates and IR Absorption Intensities of [6]-Radialene

“…The MINDO/3-FORCES treatment of [6]-radialene showed that the chair form is more stable than the planar form. It is known that this method overestimates the H f values of cyclic planar unsaturated molecules by approximately 40% [16].…”

“…Since 1962 [1] these molecules attracted much attention because of their unique properties. Thus [6]-radialene may be considered as hexamethylene cyclohexane in which all ring carbons are sp 2 -hybridized.…”

“…The synthesis and characterization of [6]-radialene were performed applying different experimental techniques [2 -3]. Due to its instability, caused by its quick polymerization at room temperature, it was not possible to find its geometry applying X-ray diffraction.…”

“…In the present work, Dewar's MINDO/3 program [14] and the PM3 methods [15] were used for the calculation of the vibration frequencies of the two conformers of [6]-radialene. Dewar's MINDO/3 and MINDO/3-FORCES programs yielded similar results.…”