An Intermediate Cobalt(IV) Nitrido Complex and its N‑Migratory Insertion Product

Abstract

Low-temperature photolysis experiments (<i>T</i> = 10 K) on the tripodal azido complex [(BIMPN^Mes,Ad,Me)­Co^II(N₃)] (<b>1</b>) were monitored by EPR spectroscopy and support the formation of an exceedingly reactive, high-valent Co nitrido species [(BIMPN^Mes,Ad,Me)­Co^IV(N)] (<b>2</b>). Density functional theory calculations suggest a low-spin d⁵, <i>S</i> = 1/2, electronic configuration of the central cobalt ion in <b>2</b> and, thus, are in line with the formulation of complex <b>2</b> as a genuine, low-spin Co­(IV) nitride species. Although the reactivity of this species precludes handling above 50 K or isolation in the solid state, the N-migratory insertion product [(NH-BIMPN^Mes,Ad,Me)­Co^II]­(BPh₄) (<b>3</b>) is isolable and was reproducibly synthesized as well as fully characterized, including CHN elemental analysis, paramagnetic ¹H NMR, IR, UV–vis, and EPR spectroscopy as well as SQUID magnetization and single-crystal X-ray crystallography studies. A computational analysis of the reaction pathway <b>2</b> → <b>3</b> indicates that the reaction readily occurs via N-migratory insertion into the Co–C bond (activation barrier of 2.2 kcal mol^–1). In addition to the unusual reactivity of the nitride <b>2</b>, the resulting divalent cobalt complex <b>3</b> is a rare example of a trigonal pyramidal complex with four different donor ligands of a tetradentate chelatean N-heterocyclic carbene, a phenolate, an imine, and an aminebinding to a high-spin Co­(II) ion. This renders complex <b>3</b> chiral-at-metal