Evidence for carbon–hydrogen–titanium interactions: synthesis and crystal structures of the agostic alkyls [TiCl3(Me2PCH2CH2PMe2)R](R = Et or Me)

Abstract

The compounds [TiCl₃(dmpe)R](R = Me, CH₂D, or Et; dmpe = Me₂PCH₂CH₂PMe₂) have been prepared. An X-ray crystal structure determination of [TiCl₃(dmpe)Et] shows that the Ti–C–C angle of the Ti–Et moiety is 86.3(6)°. Variable-temperature n.m.r. studies show the molecule to be fluxional at room temperature. At –90 °C the n.m.r. spectra correspond to the structure found in the crystal and J(C–H) for the ethyl CH₂ hydrogens is 150.2 Hz. It is concluded that the ethyl group is bonded by a [graphic omitted] system. The crystal structure of [TiCl₃(dmpe)Me] has been determined from X-ray and neutron diffraction data. The data show the methyl group to be distorted such that it is tilted with respect to the Ti–C vector and one hydrogen atom closely approaches the Ti centre giving an angle for Ti–C–H of 93.5(2)°(neutron data). Variabletemperature n.m.r. studies show that [TiCl₃(dmpe)R](R = CH₃ or CH₂D) are fluxional but provide no evidence for differentiation of the C–H moiety of the methyl group.