MOLECULAR-STRUCTURES OF ETTICL3 AND ETTICL3(DMPE) (DMPE = ME2PCH2CH2PME2) - NEW INSIGHTS INTO BETA-AGOSTIC BONDING

Gas-phase electron diffraction (GED) results for EtTiCl3 (1) are consi stent 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 = 2.19 5(3) and the valence angles (in deg) angle TiCC 116.6(11) and angle Cl TiC = 104.6(4). These structural parameters give no hint of an unusual ethyl group geometry or agostic Ti ... H-C-beta interactions. The geo metry of the EtTi fragment is conspicuously different in the diphosphi ne complex EtTiCl3(dmpe) (dmpe = Me2PCH2CH2PMe2) (2), the crystal stru cture of which has been redetermined at low temperature (105 K) by X-r ay diffraction without the problems of pronounced disorder described i n 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 st rikingly short, confirming a beta-agostic interaction.