M. Gomberg, J. Am. Chem. Soc. 22, 757 (1900).

Formation of free radicals by abstraction of the halogen from triarylmethyl halides with metals:

A. R. Forrester et al., in Organic Chemistry of Stable Free Radicals (Academic Press, New York, 1968); Scholle, Rozantsev, Russ. Chem. Rev. 42, 1101 (1973); J. M. McBride, Tetrahedron 30, 2009 (1974).