Titanocene pentasulfide explained

Titanocene pentasulfide is the organotitanium compound with the formula (C₅H₅)₂TiS₅, commonly abbreviated as Cp₂TiS₅. 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.

Preparation and structure

Titanocene pentasulfide is prepared by treating Cp₂TiCl₂ with polysulfide salts:^[1] It was first produced by the addition of elemental sulfur to titanocene dicarbonyl:^[2]

(C₅H₅)₂Ti(CO)₂ +  S₈ → (C₅H₅)₂TiS₅ + 2 CO

The complex is viewed as a pseudotetrahedral complex of Ti(IV). The Ti–S distances are 2.420 and 2.446 Å and the S–S bond distances are of a normal range, 2.051–2.059 Å.^[3] The molecule exhibits a dynamic NMR spectrum owing to the chair–chair equilibrium of the TiS₅ ring which equivalizes the Cp signals at high temperatures.^[4]

Reactions

Cp₂TiS₅ reacts with sulfur and selenium chlorides, E_xCl₂, to afford titanocene dichloride and various S_5+x and S₅Se_x rings. Illustrative is the synthesis of S₇ from disulfur dichloride:^[5]

(C₅H₅)₂TiS₅ + S₂Cl₂ → (C₅H₅)₂TiCl₂ + S₇

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.^[6]

Notes and References

1. Book: Alan . Shaver . James M. . McCall . Gabriela . Marmolejo . Inorganic Syntheses . Cyclometallapolysulfanes (And Selanes) of Bis(η ⁵ -Cyclopentadienyl) Titanium(IV), Zirconium(IV), Molybdenum(IV), and Tungsten(IV) . . 1990 . 27 . 59–65 . 10.1002/9780470132586.ch11. 978-0-470-13258-6 .
2. π-Complexes of Group IVA metals with cyclopentadiene, indene, and fluorine . . 1966 . 11 . 3548–64.
3. E. F. . Epstein . I. . Bernal . Pentachalcogenide dianions in transition-metal complexes: crystal structure of bis-(π-cyclopentadienyl)titanium pentasulphide . . 1970. 1970. 7 . 410–411. 10.1039/C29700000410.
4. Alan . Shaver . James M. . McCall . Preparation and Variable-Temperature NMR Studies of the Metallacyclosulfanes Cp₂MS₅ and (MeSCp)MS₃, Where M = Ti, Zr, and Hf. Organometallics . 1984 . 3 . 12 . 1823–1829 . 10.1021/om00090a008 .
5. Solid Sulfur Allotropes Sulfur Allotropes. Ralf . Steudel. Bodo. Eckert. Topics in Current Chemistry . 2003 . 230 . 1–80 . 10.1007/b12110.
6. Book: Advanced Inorganic Chemistry . 6th. F. Albert . Cotton. Geoffrey . Wilkinson. Carlos A. . Murillo. Manfred . Bochmann. Wiley. 1999. 978-0-471-19957-1.