Structure, optical resolution, and conformational stability of perchlorotriphenylamine

Abstract

The structure of perchlorotriphenylamine has been determined by X-ray analysis. Because this molecular propeller occupies a crystallographic site of C2 symmetry, the nitrogen atom is located in the plane of the neighboring carbon atoms. Partial resolution was achieved by chromatography on microcrystalline cellulose triacetate. Perchlorotriphenylamine thus becomes the first example of an optically active compound of the type 3 or A^ZX in which Z is not a chiral center. The compound is optically stable under ordinary conditions, and elevated temperatures are required for racemization. The activation energy (£a) for this process, 28.0 kcal/mol, slightly exceeds an empirical force field estimate of 25-27 kcal/mol calculated for the racemization barrier in the sterically similar trimesilylamine.

A Simple Route to 4-aryl and 4-hetaryl substituted 6-methyl-2,2-difluoro-1,3,2-(2H)-dioxaborines

“…The central nitrogen in compound 10 is almost planar (sum of bond angles is 359.5°) and located 5.7 pm above the plane through C(1)-C(11)-C(21). Two of the phenyl rings are turned only moderately from coplanarity with the central nitrogen (26° and 31° resp., for ring A and B) while the larger rotation of the third ring C (58°) compares well with the distortion angles reported for other substituted triphenylamines [17]. Push-pull interaction between the nitrogen donor and the electron-accepting dioxaborine groups is more pronounced in the former case, because the C-N bond lengths emanating from ring A and B amount to 140.4 pm and are shorter then those usually found in neutral triphenylamines [18].…”

Comparison of twists in isosteric propellers: X-ray structures of tris(2,6-dimethoxyphenyl)borane, tris(2,6-dimethoxyphenyl)methyl cation and tris(2,6-dimethoxyphenyl)methyl radical

“…Increased racemization barriers are consistent with large ortho substituents; perchlorotriphenylmethyl does not racemize on the room temperature time scale (Ballester, Riera, Castaner, Badia & Monsr, 1971;Hayes, Nagamo, Blount & Mislow, 1980). It was therefore surprising to us to have found an aryl twist of 12 ° in (3), a per-ortho-substituted triarylmethyl.…”

Aryl ring twists in tris(2,6-dimethoxyphenyl)-z tripod ethers: X-ray analysis of an isostructural series of triarylpropellers

“…Intramolecular congestion, which apparently blocks the formation of tris(2,6-dimethylphenyl)amine and trimesitylamine by the usual condensation methods [7], evidently does not prohibit triarylamine formation in this system. However, prolonged reaction times did result in formation of the cyclized amine 3; similar ring closures have been used to prepare 9-(2,6-dimethoxyphenyl)-l,8-dimethoxyxanthydrol and sesquixanthydrol from tris(2,6-dimethoxyphenyl)methanol [8].…”