n-butyl lithium in tetrahydrofuran; hexane byproducts: LiCl; Sep. cooling (THF, -78°C) of Cp2ZrCl2 under Ar with stirring and of Sn-compd. Dropwise addn. of n-BuLi to stannane and after 10 min at -78°C rapid addn. of mixt. to Cp2ZrCl2 soln. Stirring (1 h, -78°C), warming (room temp.).; Evapn. of mixt. gives oil solidified on standing, washing (hexane) to remove Bu4Sn, extn. (C6H6), removal of LiCl by filtn., evapn., washing (hexane) and vac. drying. Elem. anal.;