Molecular structures of EtTiCl3 and EtTiCl3(dmpe) (dmpe = Me2PCH2CH2PMe2):: New insights into β-agostic bonding

Gas-phase electron diffraction (GED) results for EtTiCl3 (1) are consistent with a molecular model of C-s symmetry, with the bond distances (r(a) in Angstrom) Ti-C = 2.090(15), C-C = 1.526(11), and Ti-Cl = 2.195(3) and the valence angles (in deg) angle TiCC 116.6(11) and angle ClTiC = 104.6(4). These structural parameters give no hint of an unusual ethyl group geometry or agostic Ti ... H-C-beta interactions. The geometry of the EtTi fragment is conspicuously different in the diphosphine complex EtTiCl3(dmpe) (dmpe = Me2PCH2CH2PMe2) (2), the crystal structure of which has been redetermined at low temperature (105 K) by X-ray diffraction without the problems of pronounced disorder described in an earlier report. Here the TiCC valence angle at 84.57(9)degrees is acute, and the Ti ... C-beta distance at only 2.501(2) Angstrom is strikingly short, confirming a beta-agostic interaction.