Vanadium tetrachloride is the inorganic compound with the formula VCl<sub>4</sub>. This reddish-brown liquid serves as a useful reagent for the preparation of other vanadium compounds.
With one more valence electron than diamagnetic TiCl<sub>4</sub>, VCl<sub>4</sub> is a paramagnetic liquid. It is one of only a few paramagnetic compounds that is liquid at room temperature.
VCl<sub>4</sub> is prepared by chlorination of vanadium metal. VCl<sub>5</sub> does not form in this reaction; Cl<sub>2</sub> lacks the oxidizing power to attack VCl<sub>4</sub>. VCl<sub>5</sub> can however be prepared indirectly from VF<sub>5</sub> at âÂÂ78 ðC.
Consistent with its high oxidizing power, VCl<sub>4</sub> reacts with HBr at -50 ðC to produce VBr<sub>3</sub>. The reaction proceeds via VBr<sub>4</sub>, which releases Br<sub>2</sub> during warming to room temperature.
VCl<sub>4</sub> forms adducts with many donor ligands, for example, VCl<sub>4</sub>(THF)<sub>2</sub>.
It is the precursor to vanadocene dichloride.
In organic synthesis, VCl<sub>4</sub> is used for the oxidative coupling of phenols. For example, it converts phenol into a mixture of 4,4'-, 2,4'-, and 2,2'-biphenols:
VCl<sub>4</sub> is a catalyst for the polymerization of alkenes, especially those useful in the rubber industry. The underlying technology is related to ZieglerâÂÂNatta catalysis, which involves the intermediacy of vanadium alkyls.