Metal- versus Ligand-Centered Reactivity of a Cobalt-Phenylenediamide Complex with Electrophiles

A new series of CoIII–CF3n+ complexes supported by a bidentate redox-active ligand with is presented. The cationic Co–CF3+ complex was first obtained by reacting CpCo(tBuUreaopda) (Cp = cyclopentadienyl, opda = o-phenylenediamide) with an electrophilic trifluoromethyl source, for which the redox-active phenylenediamide ligand serves as a 2e– reservoir to generate CpCp(tBuUreabqdi)(CF3)+ (bqdi = benzoquinonediimine). Electrochemical studies of Co–CF3+ revealed two reversible 1e– reductions. Chemical reduction with 1 or 2 equiv. reducing agent enabled isolation of the neutral and anionic complexes, respectively, where the CoIII–CF3 bond remains intact in all three oxidation states (n = +1, 0, −1). Structural analysis shows systematic changes to the redox-active ligand backbone upon reduction, consistent with sequential ligand-centered electron transfer in the series bqdi0 to s-bqdi•– to opda2–. In contrast, the reaction of CpCo(tBuUreaopda) with alkyl triflates resulted in ligand-centered alkylation at the ureayl groups instead of the targeted Co–alkyl bond formation, suggesting less favorable bond formation at cobalt and greater nucleophilic accessibility of the ligand compared to the metal center.