Synthesis and Characterization of Two "Tied-Back" Lithium Ketimides and Isolation of a Ketimide-Bridged [Cr 2 ] 6+ Dimer with Strong Antiferromagnetic Coupling.

Reaction of 1 equiv of KN(SiMe ₃ ) ₂ with 9-fluorenone results in the formation of (Me ₃ Si)N═C ₁₃ H ₈ ( 1 ) in high yield after work-up. Addition of 1 equiv of phenol to 1 results in rapid desilylation and formation of 9-fluorenone imine, HN═C ₁₃ H ₈ ( 2 ). Subsequent reaction of 2 with 1 equiv of LiN ⁱ Pr ₂ results in deprotonation and formation of [Li(Et ₂ O)] ₄ [N═C ₁₃ H ₈ ] ₄ ( 3 ) in good yield. Reaction of 1 equiv of KN(SiMe ₃ ) ₂ with 2-adamantanone for 7 days at room temperature results in the formation of (Me ₃ Si)N═C ₁₀ H ₁₄ ( 4 ) in good yield. Dissolution of 4 in neat MeOH results in rapid desilylation concomitant with formation of 2-adamantanone imine, HN═C ₁₀ H ₁₄ ( 5 ). Subsequent reaction of 5 with 1 equiv of LiN ⁱ Pr ₂ results in formation of [Li(THF)] ₄ [N═C ₁₀ H ₁₄ ] ₄ ( 6 ). Both 3 and 6 were characterized by X-ray crystallography. Finally, reaction of CrCl ₃ with 3.5 equiv of 6 results in formation of the [Cr ₂ ] ⁶⁺ dimer, [Li][Cr ₂ (N═C ₁₀ H ₁₄ ) ₇ ] ( 7 ), which can be isolated in modest yield after work-up. Complex 7 features a Cr-Cr bond length of 2.653(2) Å. Additionally, solid-state magnetic susceptibility measurements reveal strong antiferromagnetic coupling between the two Cr centers, with J = -200 cm ^-1 .