Toward Hexaphenylethane: Structure and Decomposition of Crystalline Triphenylmethyl Iodide

Triphenylmethyl iodide
(C19H15I) crystallizes in the monoclinic
system:  a = 15.919(6) Å,
b = 10.826(6) Å, c = 19.397(11)
Å, β = 114.86(4)°, space group C2/c,
Z = 8. In the structure,
heterochiral propeller molecules are interdigitated. This
arrangement, coupled with earlier
reports of the thermal instability of triphenylmethyl iodide, suggested
a convenient,
topochemically controlled, solid-state synthesis of the elusive
hydrocarbon hexaphenylethane.
Crystals of the 13Cmethyl-labeled
triphenylmethyl iodide were heated to 100 °C in a rotor
spinning at the magic angle within an NMR spectrometer. Spectral
changes and accompanying analyses by plasma desorption mass spectrometry, calorimetry, and
ESR spectroscopy
reveal that the major product in the decomposition is triphenylmethane,
produced by
hydrogen atom abstractions from neighboring triphenylmethyl radicals,
that subsequently
oligomerize. These data provide a new view of the thermal
stability of triphenylmethyl iodide
in the solid state and an old view of the accessibility of
hexaphenylethane.