Stabilizing High-Valent Metal Ions with a Ketimide Ligand Set: Synthesis of Mn(NCtBu2)4

Reaction of MnCl2 with 4 equiv of Li(NCtBu2) generates [Li(THF)]2[Mn(NCtBu2)4] (1) in 80% yield. Oxidation of 1 with 0.5 equiv of I2 produces [Li][Mn(NCtBu2)4] (2) in 88% yield. Both complexes 1 and 2 exhibit tetrahedral structures about the Mn center in the solid-state, as determined by X-ray crystallography. Reaction of 2 with 12-crown-4 generates [Li(12-crown-4)2][Mn(NCtBu2)4] (3) in 94% yield. Interestingly, in the solid-state, complex 3 exhibits a squashed tetrahedral structure about Mn. Addition of 1 equiv of I2 to 1 generates the Mn(IV) ketimide, Mn(NCtBu2)4 (4), in 75% yield. Complex 4 was fully characterized, including analysis by X-ray crystallography and cyclic voltammetry. Like 3, complex 4 also exhibits a squashed tetrahedral structure in the solid-state. Interestingly, thermolysis of complex 4 at 50 °C for 6 h results in the formation of Mn3(NCtBu2)6 (6), which can be isolated in 49% yield. Also observed in the reaction mixture is pivalonitrile, isobutylene, and isobutene, the products of ketimide ligand oxidation. We have also synthesized the homoleptic Cr(IV) ketimide complex, Cr(NCtBu2)4 (5), and have analyzed its electrochemical properties with cyclic voltammetry.