Amidation of (pentamethylcyclopentadienyl)zirconium trichloride with lithium dimethylamide; (pentamethylcyclopentadienyl)zirconium tris(dimethylamide)

Andrew Gott (A.L.Gott@warwick.ac.uk),
A contribution from the Scott Group, University of Warwick

Chemicals Used
Cp*ZrCl₃ (sublimed at 135^oC and 10^-6 mm Hg prior to use) toluene (distilled from Na and rigorously degassed before use) LiNMe₂ (Chemat Technology, 99.9%)

Procedure
A Schlenk tube was charged with Cp*ZrCl₃ (2.30 g, 6.9 mmol) and lithium dimethylamide (1.05 g, 20.7 mmol). Toluene (50 mL) was added, and the resulting yellow suspension stirred at room temperature overnight. After this time, the suspension was filtered through a Celite-packed frit and the solids washed with toluene until the washings were colourless. The toluene was removed in vacuo and the residue redissolved in pentane and transferred by cannula to a sublimation tube. The pentane was carefully removed in vacuo (very slowly, or otherwise it will bump, if this happens condense the pentane using cotton wool and liquid nitrogen). The resulting yellow solid was sublimed at 120^oC and 10^-3 mm Hg to yield the title compound as a slightly waxy yellow solid. Yield: 1.67 g, 67%

Author's Comments
The Cp*ZrCl₃ was prepared by the method of Wolczanski and Bercaw; Organometallics, 1982, 1, 793-799. The solvent must be thoroughly degassed before use. LiNMe₂ is extremely sensitive to oxygen and will decompose in oxygenated solvents, thus affecting the yield. The original reference states hexane was the reaction solvent- I have used heptane (distilled from K) to perform this procedure many times, but find that toluene works just as well. The yield is reduced from the 90% reported in the lead reference, but no sublimation was carried out in this case. The analogous Ti precursor can also be prepared by this method.

Data
¹H NMR (C₆D₆, 293K): 1.97 ppm (s, 15H, C₅Me₅), 2.92 ppm (s, 18H, 3 x NMe₂)

Lead Reference
A. M. Irigoyen, A. Martin, M. Mena, F. Palacios and C. Yelamos, J. Organomet. Chem., 1995, 494, 255-259

Other References

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