An Unusual Cobalt Azide Adduct That Produces a Nitrene Species for Carbon-Hydrogen Insertion Chemistry

A family of Co(II) complexes supported by the bulky, dianionic bis(pyrrolyl)pyridine pincer ligand pyrr2py [pyrr2py(2-) = 3,5-(t)Bu2-bis(pyrrolyl)pyridine] are reported in this work. These compounds include 1-OEt2, 1·toluene, and 1-N3Ad (Ad = 1-adamantyl), the latter which is prepared via addition of N3Ad to 1-OEt2 [1 = (pyrr2py)Co]. While complexes 1-OEt2 and 1-N3Ad are four-coordinate systems having a Co(II) ion confined in a cis-divacant octahedral geometry, complex 1·toluene possesses a Co(II) ion in a T-shaped environment where the toluene is interstitial and intercalated between two (pyrr2py)Co molecules. Complex 1-N3Ad is notable in that the organic azide binds to the metal through γ-N in a κ(1) fashion. Photolysis of 1-N3Ad results in N2 extrusion and formation of C-H insertion product [(pyrrpypyrrNHAd)Co] (2). We propose complex 2 form via insertion of the nitrene (NAd) into one (t)Bu C-H bond, thus resulting in a pincer ligand having a pendant secondary amine. Complexes 1-OEt2, 1·toluene, and 1-N3Ad and C-H insertion product 2 have been structurally characterized, and in the case of 1-OEt2, we also present electrochemical data.