Monomeric Bis(pentamethylcyclopentadienyl)titanium(III) Complexes with Halide, Borohydride, Amide, Alkoxide, and Carboxylate Ligands: X-ray Structure of Bis(pentamethylcyclopentadienyl)titanium(III) Chloride

The synthesis and characterization of monomeric Cp*2TiX complexes (X = Cl, Br, I, BH4, OCMe3, O2CH) are reported. These 15-electron d1 systems have one unpaired electron and form perfect Curie paramagnetic systems. They are NMR and ESR active. 1H NMR spectra show broad lines (width 600-5000 Hz) for the Cp* hydrogens between 14.0 and 18.4 ppm. Observation of the protons of the non-Cp* ligands is possible if they are positioned at least β with respect to the metal. The ESR spectra are singlets (g = 1.939-1.978), with for some complexes the expected Ti isotope hyperfine splitting. Hyperfine splittings due to interaction with hydrogen or other nuclei of the ligands are not observed. The structure of Cp*2TiCl (1) was determined by X-ray diffraction. 1 crystallizes in the monoclinic space group P21/n, with a = 9.339 (2) Å, b = 13.632 (1) Å, c = 15.140 (3) Å, β = 99.55 (1)°, and Z = 4. The structure was refined to R = 0.045 and Rw = 0.050 for 290 parameters and 2909 observed reflections (with F > 3σ(F)). The molecule exhibits an approximate twofold noncrystallographic axis along the Ti-Cl bond. The chlorine ligand is coordinated in the equatorial plane of a bent-sandwich permethyltitanocene fragment (Ti-Cl = 2.363 (1) Å). The Cp* rings coordinate in a true η5 way to the metal. Methyl-methyl contacts between the staggered Cp* ligands cause a deviation of one of the methyl groups out of the plane of the ring and away from the metal of 0.40 (1) Å.