in 1,4-dioxane; toluene Ar atmosphere; cooling soln. of ligand (-78°C), mixing with soln. of n-BuLi (-78°C), warming to room temp. (2 h), cooling to -78°C, addn. of ZrCl4, warming to room temp., stirring (overnight); filtration (Celite), washing (toluene), solvent removal; elem. anal.;