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

Reaction of 1 equiv of KN(SiMe) with 9-fluorenone results in the formation of (MeSi)N═CH () in high yield after work-up. Addition of 1 equiv of phenol to results in rapid desilylation and formation of 9-fluorenone imine, HN═CH (). Subsequent reaction of with 1 equiv of LiNPr results in deprotonation and formation of [Li(EtO)][N═CH] () in good yield. Reaction of 1 equiv of KN(SiMe) with 2-adamantanone for 7 days at room temperature results in the formation of (MeSi)N═CH () in good yield. Dissolution of in neat MeOH results in rapid desilylation concomitant with formation of 2-adamantanone imine, HN═CH (). Subsequent reaction of with 1 equiv of LiNPr results in formation of [Li(THF)][N═CH] (). Both and were characterized by X-ray crystallography. Finally, reaction of CrCl with 3.5 equiv of results in formation of the [Cr] dimer, [Li][Cr(N═CH)] (), which can be isolated in modest yield after work-up. Complex 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 = -200 cm.