Synthesis and structure of Cp2*TiH, Cp2*TiH2Li(tmed), and [Cp2*TiOLi(THF)]2

The solid-state crystal structure of the d1 hydride Cp2*TiH shows that it has a bent sandwich structure with an open Cp*(centroid)-Ti-Cp*(centroid) angle of 150°. The crystal structure contains two molecules in the asymmetric unit, and the hydridic hydrogen atom is located and refined with isotropic thermal parameters to a Ti-H distance of 1.69(5) and 1.84(4) angstrom in each independent molecule; the average Ti-H distance is 1.76 angstrom. In each molecule, the Ti-H vector lies on the idealized C2 axis of the bent metallocene. The addition of n-BuLi and Me2NCH2CH2NMe2 (tmed) in hexane to Cp2*TiH or the addition of [Li(tmed)]2C10H8 to Cp2*TiCl gives the anionic dihydride Cp2*Ti(μ-H)2Li(tmed). The hydride atoms are not located in the X-ray diffraction experiment, but electron paramagnetic resonance spectra show coupling to two equivalent hydrogen nuclei, AHiso = 9.6 G. In addition, coupling to 7Li, confirmed by the preparation of the 6Li isotopomer, shows that the unpaired electron couples with each hydridic hydrogen and lithium nucleus. The proposed structure has two hydride ligands bridging the Cp2*Ti and Li(tmed) fragments. Water in tetrahydrofuran (THF) reacts with Cp2*Ti(μ-H)2Li(tmed) to give the dimer, [Cp2*TiOLi-(THF)]2. Its X-ray structure shows that the two Cp2*TiO fragments are joined together by the Li(THF) fragments such that the Li2O2 unit is a square as found in dimeric lithium alkoxides; in this case, the alkoxide is the metallocene Cp2*TiO-. Variable-temperature magnetic susceptibility shows that the unpaired electrons on each Cp2*TiO- fragment are not coupled down to 5 K.