Vanadium oxytrichloride

Vanadium oxytrichloride is VOCl3. It is a distillable liquid, which hydrolyzes readily in air (see picture). VOCl3 is a vanadium(V) compound and as such 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 1.57 and 2.14 Å, respectively.

Properties
VOCl3 is highly reactive toward water and evolves Cl2 upon standing. Although VOCl3 reacts with hydroxylic solvents (see below), it is soluble in hydrocarbons such as benzene, CH2Cl2, and hexane.

In many aspects, the chemical properties of VOCl3 and POCl3 are similarly shaped molecular compounds. 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 ca. 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 entails 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 react with alcohols especially in the presence of a proton-acceptor (e.g. Et3N) to give esters
 * 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

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