Oxygenated Titanium Sulfide Clusters. Synthesis and Structures of (CH₃C₅H₄)₄Ti₄S₈O_x(x = 1, 2)

The reaction of Li₂S₂ with (CH₃C₅H₄)TiCl₃ followed by exposure to oxygen gives both (CH₃C₅H₄)₄Ti₄S ₈O (1) and (CH₃C₅H₄)₄Ti₄S ₈O₂ (2). Also isolated was the mixed-ligand complex (C₅H₅)(CH₃C₅H₄) ₃Ti₄S₈O₂ (2″), which arises from an impurity in the starting material. Compound 1 can be converted to 2 by using (NBu₄)IO₄, m-chloroperoxybenzoic acid, and tert-butyl hydroperoxide. Experiments with 1 and its (C₅H₅) analogue indicate that this transformation occurs without cluster fragmentation. The compounds were purified chromatographically and were characterized by spectroscopic and, for 2, crystallographic methods. ¹H NMR studies over the temperature range -70 to +90°C show that 1 is dynamic, as the methyl groups give rise to four resonances at low temperatures that merge into three resonances at higher temperatures. The ¹H NMR spectrum of 2, which does not vary over the temperature range of +80 to -70°C, shows two methyl resonances and eight cyclopentadienyl ring proton resonances, two of which are coincident. Relative to 2, the ¹H NMR spectrum of 2″ shows the following differences: (i) one of the two methyl resonances is halved in intensity and is shifted upfield, (ii) three of the eight ring proton resonances are halved in intensity, and (iii) one of the eight ring proton resonances overlaps with the single C₅H₅ peak. Complex 2 crystallizes in the trigonal space group P3₁21 with a = 10.700 (2) Å, c = 22.530 (6) Å, V = 2233.9 (9) ų, and ρ_obsd = 1.75 g/cm³ (ρ_calcd = 1.77 g/cm³ for Z = 3). The structure was solved by direct methods leading to a final R = 0.0234 (R_w = 0.0246) with all non-hydrogen atoms anisotropic. The molecule possesses crystallographic C₂ symmetry and consists of a Ti₄(μ₄-O) core with two Ti atoms further bridged by an oxo ligand. Each of the four faces of the tetrahedral Ti₄O core is capped by a μ₃-S₂ ligand.