Work

Minisci Substitution with C–C Bond Formation in Reactions of Trityl Radicals with a Ruthenium-Bound Pyridyl-Imidazole Ligand

Year: 2025

Type: article

Abstract: Carbon radicals are key to many biological and organic reactions, and stable triphenylmethyl (trityl) radicals are often used to model these processes. Here, we report reactions of a Ru III -pyridine-imidazolate complex (Ru III (pyIm), where pyIm = pyridine-imidazolate) with a series of para-substituted trityls (R = MeO, t Bu, Ph, and CF 3 ) that surprisingly proceed via C–C bond formation. Reactions of metal complexes with carbon radicals more commonly form C–X bonds (X = O, N, or halide), as in the ubiquitous rebound mechanism. Ru III (pyIm), however, reacts by a Minisci-type substitution to form Ru II (5-trityl-imidazole) complexes. The reduced imidazole complexes can be oxidized to the corresponding Ru III (5-trityl-imidazolate) by abstraction of the imidazole NH hydrogen by an additional trityl. These reactions form triphenylmethanes and a mixture of tritylated Ru II and Ru III complexes. The imidazolate is rendered electrophilic, as required for Minisci reactions, by the Ru III center that accepts 1 e – in the reaction. Alternatively, the reaction can be viewed as a trityl radical coupling with the Ru III (pyIm) SOMO that has contributions from the imidazolate π-HOMO and a half-filled t 2g orbital on Ru III . Because of kinetic competition between the C–C bond formation and H-abstraction steps, more electron-rich trityls form mostly Ru II -trityl-imidazoles, while electron-poor trityls form Ru III -trityl-imidazolates.

Source: Inorganic Chemistry

DOI: 10.1021/acs.inorgchem.5c02512