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.