Mixed chloro(dialkylamido) complexes of zirconium and hafnium

Chloro(dialkylamido) complexes of the type (R(2)N)(2)MCl(2)(THF)(2) (R = Me, Et; M = Zr and R = Me; M = Hf) were synthesized in a conproportionation reaction by adding an equimolar amount of the corresponding M(NR(2))(4) to an ether slurry of MCl(4) in the presence of THF. X-ray crystal structure determinations of (Et(2)N)(2)ZrCl2(THF)(2) (1a) and (Me(2)N)(2)ZrCl2 (THF)2 (1b) reveal a distorted octahedral coordination geometry where the sterically demanding dialkylamide ligands force the chloride and the THF ligands out of their ideal position. Dynamic NMR investigations indicate an equilibrium of complexes with coordinated THF at low temperature in accordance with the structure determined by X-ray crystallography and of chloro-amido complexes that do not bind THF (at higher temperature).