Preparation and structures of methyltitanium compounds

[Ti(CH3)(4)] and its derivatives [Ti(CH3)(5)](-), [Ti-2(CH3)(9)](-), [Ti(CH 3)(3)Cl], [Ti(CH3)(2)Cl-2] and [Ti(CH3)Cl-3] have been prepared and charact erized structurally. [Ti(CH3)(4)] can be crystallized only as a solvate [Ti (CH3)(4)]. Et2O that has a trigonal-bipyramidal structure with an apically positioned oxygen. For unsolvated [Ti(CH3)(4)] ab initio calculations predi ct a tetrahedral structure, but distortion to a trigonal pyramid does not r equire much energy. [Ti(CH3)(5)](-) is predicted to have a tetragonal-pyram idal structure, but it appears in two separate forms in the crystal. One fo rm is close to a tetragonal pyramid, the other to a trigonal bipyramid. [Ti -2(CH3)(9)](-) can be viewed as a double trigonal bipyramid that is formed from [Ti(CH3)(4)] and [Ti(CH3)(5)](-) bridged by one methyl group. Solvent- free [Ti(CH3)(3)Cl] is a tetramer with a cube-like structure, while [Ti(CH3 )(3)Cl] . Et2O is trigonal bipyramidal. [Ti(CH3)(2)Cl-2] forms chains of ci s-dichloro-bridged octahedra, and [Ti(CH3)Cl-3]. Et2O is a cis-dichloro-bri dged dimer. In none of these structures is any indication found of an agost ic interaction between a methyl group and an adjacent titanium atom. In [Ti -2(CH3)(9)](-) the interaction between the [Ti(CH3)(4)] and [Ti(CH3)(5)](-) can be described as agostic with respect to the bridging methyl group and the second titanium atom.