Amidation of (pentamethylcyclopentadienyl)zirconium trichloride with lithium dimethylamide; (pentamethylcyclopentadienyl)zirconium tris(dimethylamide)SyntheticPage 232 (2005)
A contribution from the Scott Group, University of Warwick
Cp*ZrCl3 (sublimed at 135oC and 10-6 mm Hg prior to use) toluene (distilled from Na and rigorously degassed before use) LiNMe2 (Chemat Technology, 99.9%)
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 120oC and 10-3 mm Hg to yield the title compound as a slightly waxy yellow solid. Yield: 1.67 g, 67%
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.
1H NMR (C6D6, 293K): 1.97 ppm (s, 15H, C5Me5), 2.92 ppm (s, 18H, 3 x NMe2)
A. M. Irigoyen, A. Martin, M. Mena, F. Palacios and C. Yelamos, J. Organomet. Chem., 1995, 494, 255-259
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|guoliang - 11 Apr 2006 07:08:40
ti's very good!