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.