Terminal Zirconium Imides Prepared by Reductive C−N Bond Cleavage

Toluene reflux of ZrCl₄ with Li(Nacnac) (Nacnac^- = [Ar]NC(<i>t</i>Bu)CHC(<i>t</i>Bu)N[Ar], Ar = 2,6-[CH(CH₃)₂]₂C₆H₃) provides the complex (Nacnac)ZrCl₃ in 75% yield. Cl^- substitution for OTf^- is readily achieved with 3 equiv of AgOTf to yield 77% of the complex (Nacnac)Zr(OTf)₂(η²-OTf). The coordination mode of the three triflato groups was determined by a combination of single-crystal X-ray analysis and ¹⁹F COSY experiments. Addition of 2 equiv of LiCH₂XMe₃ (X = C, Si) to (Nacnac)ZrCl₄ in Et₂O affords the bis(alkyl) systems (Nacnac)Zr(CH₂XMe₃)₂Cl in good yield (X = C, 86%; X = Si, 91%). In contrast, reaction of (Nacnac)Zr(OTf)₂(η²-OTf) with 2 equiv of LiCH₂CMe₃ leads instead to formation of the terminal zirconium−imido complex [(Nac<i>t</i>Bu)ZrNAr(μ₂-OTf)]₂ (Nac<i>t</i>Bu^- = [2,6-(CHMe₂)₂C₆H₃]NC(<i>t</i>Bu)CHC(<i>t</i>Bu)). Likewise, reduction of (Nacnac)ZrCl₃ with 2 equiv of KC₈ in THF also affords a terminal zirconium−imido species, (Nac<i>t</i>Bu)ZrNAr(Cl)(THF). The zirconium−imido compounds described herein result from reductive cleavage of the C−N bond of the imine functionality contained in the Nacnac^- ligand. The complexes (Nacnac)ZrCl₃, (Nacnac)Zr(OTf)₂(η²-OTf), (Nacnac)Zr(CH₂XMe₃)₂Cl, [(Nac<i>t</i>Bu)ZrNAr(μ₂-OTf)]₂, and (Nac<i>t</i>Bu)ZrNAr(Cl)(THF) have been fully characterized, and a single-crystal X-ray diffraction analysis is reported for each.