Synthesis and X-ray crystal structures of ansa-complexes of titanium, zirconium, and hafnium involving methylene-bis(indenyl) ligand

Synthesis of bis(indenyl)methane and the corresponding ansa-complexes of titanium(IV), zirconium(IV), and hafnium(IV) was performed. Mixtures of rac- and meso-methylene-bis(indenyl)zirconium and -hafnium dichlorides were obtained under a treatment of the respective metal tetrachlorides with bis[3-(tri-n-butyltin)indenyl]methane in toluene. The complexes, rac-H2C(indenyl)2MCl2, were isolated in 27% (M=Zr) and 31% (M=Hf) yields using a simple work-up process. These zirconium and hafnium complexes were characterized by X-ray crystal structure analysis. Methylene-bis(indenyl)titanium(IV) dichloride was prepared by two different pathways. The first one includes a treatment of TiCl4(THF)2 with dilithium salt of bis(indenyl)methane in THF. This procedure gives rac-H2C(indenyl)2TiCl2 in 16% only. An alternative reaction involving a treatment of TiCl4 with bis[3-(tri-n-butyltin)indenyl]methane results in rac-H2C(indenyl)2TiCl2 with 38% yield. A treatment of rac-H2C(indenyl)2TiCl2 with two equivalents of MeLi in diethyl ether gives rac-H2C(indenyl)2TiMe2, which has been isolated in 64% yield, and characterized by X-ray crystal structure analysis.