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

Triphenylmethyl (trityl, Ph 3 C•) radicals have been considered the prototypical carbon-centered radical since their discovery in 1900. Tris(4-substituted)-trityls [(4-R-Ph) 3 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) 3 C•, where R = NMe 2 , OCH 3 , t Bu, Ph, Cl, and CF 3 . 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) 3 CCl or (RPh) 3 CBr, by controllably removing the halide with subsequent 1e - reduction of the trityl cation, (RPh) 3 C + . These syntheses afford consistently crystalline trityl radicals of high purity for further studies.