Titanocene pentasulfide is the organotitanium compound with the formula (C<sub>5</sub>H<sub>5</sub>)<sub>2</sub>TiS<sub>5</sub>, commonly abbreviated as Cp<sub>2</sub>TiS<sub>5</sub>, where Cp stands for cyclopentadienyl. This metallocene exists as a bright red solid that is soluble in organic solvents. It is of academic interest as a precursor to unusual allotropes of elemental sulfur as well as some related inorganic rings.
Titanocene pentasulfide is prepared by treating Cp<sub>2</sub>TiCl<sub>2</sub> with polysulfide salts: It was first produced by the addition of elemental sulfur to titanocene dicarbonyl:
The complex is viewed as a pseudotetrahedral complex of Ti(IV). The TiâÂÂS distances are 2.420 and 2.446 àand the SâÂÂS bond distances are of a normal range, 2.051âÂÂ2.059 à. The molecule exhibits a dynamic NMR spectrum owing to the chairâÂÂchair equilibrium of the TiS<sub>5</sub> ring which equivalizes the Cp signals at high temperatures.
reacts with sulfur and selenium chlorides, E<sub>x</sub>Cl<sub>2</sub>, to afford titanocene dichloride and various S<sub>5+x</sub> and S<sub>5</sub>Se<sub>x</sub> rings. Illustrative is the synthesis of S<sub>7</sub> from disulfur dichloride:
It also reacts with alkenes and ketenes to give heterocycles composed of Ti, C and S. With trialkylphosphines, the cycle dimerize into rings of various sizes, depending on the trialkylphosphine used.