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 ¹³C_methyl-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.