Vanadium oxytrichloride

Properties

VOCl₃ is a vanadium compound with vanadium in the +5 oxidation state and as such is diamagnetic. It is tetrahedral with O-V-Cl bond angles of 111° and Cl-V-Cl bond angles of 108°. The V-O and V-Cl bond lengths are 157 and 214 pm, respectively. VOCl₃ is highly reactive toward water and evolves HCl upon standing. It is soluble in nonpolar solvents such as benzene, CH₂Cl₂, and hexane. In some aspects, the chemical properties of VOCl₃ and POCl₃ are similar. One distinction is that VOCl₃ is a strong oxidizing agent, whereas the phosphorus compound is not.

Preparation

VOCl₃ is synthesized by the chlorination of V₂O₅. The reaction proceeds at c. 600 °C:

3 Cl₂ + V₂O₅ → 2 VOCl₃ + 1.5 O₂

When the V₂O₅ is used as an intimate mixture with carbon, the synthesis proceeds at 200–400 °C; in this case the carbon serves as a deoxygenation agent akin to its use in the Kroll process for the manufacturing of TiCl₄ from TiO₂.

Vanadium(III) oxide can also be used as a precursor:

3 Cl₂ + V₂O₃ → 2 VOCl₃ + 0.5 O₂

A more typical laboratory synthesis involves the chlorination of V₂O₅ using SOCl₂.

V₂O₅ + 3 SOCl₂ → 2 VOCl₃ + 3 SO₂

Hydrolysis and alcoholysis

Vanadium oxytrichloride quickly hydrolyzes resulting in vanadium pentoxide and hydrochloric acid. In the picture, orange V₂O₅ can be seen forming on the walls of the beaker. An intermediate in this process is VO₂Cl:

2 VOCl₃ + 3 H₂O → V₂O₅ + 6 HCl

VOCl₃ reacts with alcohols especially in the presence of a proton-acceptor (e.g. Et₃N) to give alkoxides:

VOCl₃ + 3 ROH → VO(OR)₃ + 3 HCl (R = Me, Ph, etc.)

Interconversions to other V-O-Cl compounds

VOCl₃ is also used in the synthesis of VOCl₂.

V₂O₅ + 3 VCl₃ + VOCl₃ → 6 VOCl₂

Dioxovanadium monochloride can be prepared by an unusual reaction involving Cl₂O.

VOCl₃ + Cl₂O → VO₂Cl + 2 Cl₂

At >180 °C, VO₂Cl decomposes to V₂O₅ and VOCl₃. Similarly, VOCl₂ also decomposes to give VOCl₃, together with VOCl.

Adduct formation

VOCl₃ is strongly Lewis acidic, as demonstrated by its tendency to form adducts with various bases such as MeCN and amines. In forming the adducts, vanadium changes from four-coordinate tetrahedral geometry to six-coordinate octahedral geometry:

VOCl₃ + 2 H₂NEt → VOCl₃(H₂NEt)₂

VOCl3 in alkene polymerization

VOCl₃ is used as a catalyst or precatalytst in production of ethylene-propylene rubbers (EPDM).