A Guide to Tris(4-Substituted)-triphenylmethyl Radicals.

Triphenylmethyl (trityl, PhC•) radicals have been considered the prototypical carbon-centered radical since their discovery in 1900. Tris(4-substituted)-trityls [(4-R-Ph)C•] have since been used in many ways due to their stability, persistence, and spectroscopic activity. Despite their widespread use, existing synthetic routes toward tris(4-substituted)-trityl radicals are not reproducible and often lead to impure materials. We report here robust syntheses of six electronically varied (4-RPh)C•, where R = NMe, OCH, Bu, Ph, Cl, and CF. The characterization reported for the radicals and related compounds includes five X-ray crystal structures, electrochemical potentials, and optical spectra. Each radical is best accessed using a stepwise approach from the trityl halide, (RPh)CCl or (RPh)CBr, by controllably removing the halide with subsequent 1e reduction of the trityl cation, (RPh)C. These syntheses afford consistently crystalline trityl radicals of high purity for further studies.