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Alkylation of zirconium tetrachloride with benzyl Grignard; Zirconium tetrabenzyl

SyntheticPage 1
DOI: 10.1039/SP1
Submitted May 30, 2001, published Jun 01, 2001
Peter Scott (peter.scott@warwick.ac.uk)
A contribution from Scott group, Warwick University


			Reaction Scheme: <span id="csm1276121193272" class="csm-reaction-type" title="Alkylation">Alkylation</span> of <span id="ent634117205363955692_414201469" class="csm-chemical-name csm-ambiguous" title="zirconium tetrachloride">zirconium tetrachloride</span> with benzyl Grignard

Chemicals Used

C6H5CH2MgCl (1M in diethyl ether, Aldrich)
ZrCl4 (not sublimed)
diethyl ether (dried over Na/K but Na would do)
toluene (dried over Na)

Procedure

Using Schlenk techniques, C6H5CH2MgCl (100 ml, 1M in diethyl ether, 4 equiv.) was added to ZrCl4 (6.0 g, 0.025 mol) in a diethyl ether (50 ml) slurry over 1 hr at -78°C, ensuring that the suspension was cool before addition of the Grignard reagent. Once the addition was complete, the mixture was allowed to warm slowly with stirring and any gas expansion was vented at the Schlenk line bubbler. The solution was stirred overnight at ambient temperature (in the absence of light) and the bright orange solution was then cooled to 0°C and filtered to remove MgCl2 [this residue should be "destroyed" by cautious hydrolysis before disposal]. The diethyl ether was removed in vacuo and the orange product was redissolved in toluene (30 ml) and filtered. Cooling to -30°C afforded orange crystals which were washed with cold toluene (2 x 10 ml). Yield variable, but about 70%.

Author's Comments

Keeping the reaction in the dark is important. Use aluminium foil. Sometimes the yield from the first crop is low and a second crop can be obtained by concentration and cooling. We store the product in the freezer in a Schlenk wrapped in foil and transfer the Schlenk to the glovebox to handle it. If you have a freezer in the box that is ideal. Don't forget that this type of method will only work for alkyls without beta-H atoms (beta elimination).

Data

1H NMR (293 K, d6-benzene) 7.15 (m, 12H, Ph), 6.42 (d, 8H, Ph), 1.57 (s, 8H, CH2).

Lead Reference

U. Zucchini, E. Albizatti and U. Gianni, J. Organomet. Chem., 1971, 26, 357.

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  • Registered user Max HammondFeb 16 2002 7:19PM

    The reaction is conducted with rigorous exclusion of air and water (Schlenk Procedures)

  • Registered user Peter ScottApr 19 2005 3:18PM

    We have generally used e.g. Aldrich ZrCl4 (99.5+) for this reaction. Note that if you are unsure of the purity of the ZrCl4 you should source some clean material or sublime some. ZrCl4 is pretty air sensitive, so if your jar is on a shelf in the lab then it is probably mostly "ZrCl2O" etc.. It would be inetresting to hear if the THF adduct ZrCl4(THF)2 is good material to use. It might be OK because the reaction is performed in ether.

  • Registered user Andrew GottApr 29 2005 3:33PM

    I suppose you could use the THF adduct, but I have used the ether adduct ZrCl4(OEt2)2 in this prep in the past. The ether adduct is prepared the same way as the THF analogue

  • Registered user Sara RoncaJun 29 2009 11:14AM

    I have tried to use benzyl magnesium chloride 2.0M in THF but it didn't work properly. I then discovered that THF can coordinate to the zirconium tetrabenzyl and the resulting adduct is insoluble in toluene (J. Organomet. Chem., 1974, 74, pag 417).

    • Registered user Peter ScottMar 9 2010 12:47PMTHF

      Since this time we have made Zr tetrabenzyl by this method many times using ZrCl4 and the Grignard in ether.

  • Guest danaOct 23 2012 1:49PMstirring over night

    Do you leave the reaction over night at -78C as well? or you let it reach to R.T, and then when u want to filter you cool it again to 0C?

    • Registered user Peter ScottOct 23 2012 3:59PM

      The method described cooling to 0oC, so no it was not stirred at -78 overnight. Nevertheless, the method has now been clarified.

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