A Pair of Cobalt(III/IV) Terminal Imido Complexes.

The reaction of the cobalt(I) complex [(TIMMN )Co ](BPh ) (2) (TIMMN =tris-[2-(3-mesitylimidazolin-2-ylidene)methyl]amine) with 1-adamantylazide yields the cobalt(III) imido complex [(TIMMN )Co (NAd)](BPh ) (3) with concomitant release of dinitrogen. The N-anchor in diamagnetic 3 features an unusual, planar tertiary amine, which results from repulsive electrostatic interaction with the filled d(z )-orbital of the cobalt ion and negative hyperconjugation with the neighboring methylene groups. One-electron oxidation of 3 with [FeCp ](OTf) provides access to the rare, high-valent cobalt(IV) imido complex [(TIMMN )Co (NAd)](OTf) (4). Despite a half-life of less than 1 h at room temperature, 4 could be isolated at low temperatures in analytically pure form. Single-crystal X-ray diffractometry and EPR spectroscopy corroborate the molecular structure and the d low-spin, S= , electron configuration. A computational analysis of 4 suggests high covalency within the Co =NAd bond with non-negligible spin density located at the imido moiety, which translates into substantial triplet nitrene character.