[Zr(NMe₂)₄] synthesis
ZrCl₄
diethyl ether
THF

A Schlenk vessel with stirrer bar was charged with [Zr(NMe₂)₄] (synthesis) (0.49 g, 1.84 mmol) and zirconium tetrachloride (0.43 g, 1.85 mmol). To this was added diethyl ether (50 ml) followed by THF (10 ml). The solution was stirred for 2 h during which time it turned a pale green colour. The solution was stirred for a further 2 h, filtered and concentrated. Upon keeping at –30 ºC for 48 h, a yellow/green crystalline solid had formed. This was filtered, washed with pentane at –78 ºC and dried in vacuo. Yield = 1.01 g, 70 %

It is sometimes noted that a fine solid remains undissolved, but upon gentle warming all solids dissolved. It's important to do this otherwise the product is contaminated with ZrCl4. See here for comments on purity of ZrCl₄.