Vanadium hexacarbonyl, reaction with

Vanadium hexacarbonyl reacts with various arenes yielding complexes [(arene)V(CO)4]" [V(CO)6] from which hexafluorphosphate or tetra-phenylborate salts can be prepared by metathesis reaction (50, 52). The cation [(CeHe)V(CO)4] reacts with NaBH4 to give the neutral cyclo-hexadienyl compound (CeH7)V(CO)4 (51). Similar results are observed with methyl-substituted derivatives. The addition of the hydride ion was shown to occur preferentially at unsubstituted positions of the aromatic ring. 

The known vanadium carbonyl cations are of two types, namely a tetracarbonyl, [AreneV(CO)4]+, and a dicarbonyl, [Cp2V(CO)2]+. The tetracarbonyl derivatives are readily prepared under mild conditions by the reaction of an arene with vanadium hexacarbonyl. The arenes used include benzene, its methyl derivatives 28, 29), naphthalene, and anisole 29). The cation is probably formed by oxidation of the intermediary arene vanadium tricarbonyl. 

---