Synthesis and Structure of Cp*₂TiH, Cp*₂TiH₂Li(tmed), and [Cp*₂TiOLi(THF)]₂

Abstract

The solid-state crystal structure of the d1 hydride Cp*2TiH 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) Å in each independent molecule; the average Ti−H distance is 1.76 Å. 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 Cp*2TiH or the addition of [Li(tmed)]2C10H8 to Cp*2TiCl gives the anionic dihydride Cp*2Ti(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 Cp*2Ti and Li(tmed) fragments. Water in tetrahydrofuran (THF) reacts with Cp*2Ti(μ-H)2Li(tmed) to give the dimer, [Cp*2TiOLi(THF)]2. Its X-ray structure shows that the two Cp*2TiO 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 Cp*2TiO-. Variable-temperature magnetic susceptibility shows that the unpaired electrons on each Cp*2TiO- fragment are not coupled down to 5 K.