Multicomponent Mechanochemical Synthesis of Cyclopentadienyl Titanium tert-Butoxy Halides, Cp x TiX y (O t Bu)4-(x+y) (x, y = 1, 2; X = Cl, Br).

Titanium tert-butoxy halides of the formula Cp x TiX y (O t Bu)4-(x+y) (x, y = 1, 2; X = Cl, Br) have been prepared thorough milling the reagents without solvent. In the case of the chloride derivatives, Cp2TiCl2 is used as a starting material; in the case of the bromides, a mixture of LiCp, TiBr4, and Li[O t Bu] is used. The stoichiometric ratios of the starting materials are reflected in the major products of the reactions. Single-crystal X-ray structures are reported for Cp2TiCl(O t Bu), Cp2TiBr(O t Bu), and CpTiBr2(O t Bu), as well as for Cp2TiCl(O i Pr) and a redetermination of Cp2TiCl(OMe). The tert-butoxy derivatives are notable for their nearly linear Ti-O-C angles (>170°) that reflect Ti-O π-bonding, an interpretation supported with density functional theory calculations.

Reaction environment and ligand lability in group 4 Cp2MXY (X, Y = Cl, OtBu) complexes.

Despite their usefulness in catalytic and materials chemistry, the mixed cyclopentadienyl/alkoxide complexes of Ti, Zr, and Hf (Cp2M(OR)2) have few reliable synthetic routes available to them. We describe the use of mechanical ball milling to promote halide metathesis from Cp2MCl2, and compare these results to those obtained in hexanes and THF. Even without solvent, ring lability is extensive with titanium complexes, and alkoxide compounds with 0-3 Cp rings are isolated. The ball milling reactions are much faster than those in solution, but the distributions of products are similar to those obtained in hexanes, although different from those in THF. The range of compounds obtained from Zr and Hf starting materials is more limited, as Cp ring exchange does not occur.