Metal- versus ligand-centered reactivity of a cobalt-phenylenediamide complex with electrophiles.

A new series of [Co ^III -CF ₃ ] ^{n +} complexes supported by a bidentate redox-active ligand is presented. The cationic [Co-CF ₃ ] ⁺ complex was first obtained by reacting [CpCo( ^{t BuUrea} opda)] (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( ^{t BuUrea} bqdi)(CF ₃ )] ⁺ (bqdi = benzoquinonediimine). Electrochemical studies of [Co-CF ₃ ] ⁺ 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 [Co ^III -CF ₃ ] 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 [bqdi] ⁰ to [s-bqdi]˙ ^- to [opda] ^2- . In contrast, the reaction of [CpCo( ^{t BuUrea} opda)] 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.