ARYL RING TWISTS IN TRIS(2,6-DIMETHOXYPHENYL)-Z TRIPOD ETHERS - X-RAY-ANALYSIS OF AN ISOSTRUCTURAL SERIES OF TRIARYLPROPELLERS

Tris(2,6-dimethoxyphenyl)amine has been synthesized and its molecular and crystal structure determined by X-ray diffraction. This structure completes the series of isosteric compounds Ar3Z, where Z = B, C, N, and Ar = 2,6-dimethoxyphenyl. Structures for the tris(2-methoxy-6-meth ylphenyl)borane and tris(2,6-dimethoxyphenyl)methyl cation triiodide ( Ar3C+I3-) are also reported. The Ar3B and Ar3N structures are isomorph ous. The triiodide and the earlier reported tetrafluoroborate salt (Ar 3C+BF4-) are also quite similar, as are the two boranes above and the known trimesitylborane, which all tend toward D3 symmetric conformatio ns. In contrast, the radical Ar3C, intermediate between Ar3B and Ar3N , is markedly unsymmetrical. Taken together, these findings support an earlier conjecture that the solid-state conformation of Ar3C does no t represent a minimum energy structure for the free radical in solutio n. Crystal seeding by radical oxidation products is offered as an expl anation for the radical's markedly unsymmetrical crystal geometry.