Vanadium compounds complexes

For the two metallocene systems, V(Cp)2 (d3), and Ni(Cp)2 (ds), the only acceptable assignments locate the 4> level between the two II levels in each case, and thus, using the data of Prins and Van Voorst (4 7), yield the parameters Ds = 3543 cm"1, Dt = 2074 cm"1 for the vanadium complex, and Ds = 3257 cm 1,Dt = 1806 cm-1 for the nickel derivative. Moreover, these authors, treating the available data for Fe(Cp)2, derived parameters corresponding to Ds = 5100 cm-1 and Dt = 2740 cm-1, from which it may be noted that, although the individual values of Ds and Dt vary appreciably from one complex to another, the ratio Dt/Ds remains approximately constant and shows the values 0.585,0.554,and 0.537 for the V, Ni, and Fe compounds respectively. More recently Sohn, Hendrickson, and Gray (48, 49) have successfully analysed the d-d spectra of several d6 systems in terms of parameters which lead to the ratios 0.525, 0.540, and 0.585 for Dt/Ds in the complexes Fe(Cp)2, Co(Cp)2+, and Ru(Cp)2 respectively, and it therefore seems reasonable to adopt an average value of 0.55 for this ratio for all metallocene systems. 

Reports have appeared claiming that triperoxo vanadates behave as nucleophilic oxidants. In particular, triperoxo vanadium complexes, A[V(02)3]3H20 (A=Na or K), are proposed as efficient oxidants of a,-unsaturated ketones to the corresponding epoxide, benzonitrile to benzamide and benzil to benzoic acid, reactions which are usually carried out with alkaline hydrogen peroxide. Subsequent studies concerning the oxidation of cyclobutanone to 4-hydroxybutanoic acid, carried out with the above-cited triperoxo vanadium compound, in alcohol/water mixtures, clearly indicated that such a complex does not act as nucleophilic oxidant, but only as a source of HOO anion. 

The +4 oxidation state is the most stable under ordinary conditions and the majority of vanadium(IV) compounds contain the V02+ unit (vanadyl ion), which can persist through a variety of reactions. Its complexes typically have square pyramidal or bipyramidal geometry... 

Vanadium(II) compounds are usually prepared by reduction of acidic solutions of higher oxidation states. The usual geometry is octahedral and the electronic spectra often show three d-d spin-allowed bands. These spectra, as well as those of tetrahedral and linear complexes, have been reviewed.58 For this cr configuration, a spin-only magnetic moment of 3.87 BM is expected. Slow substitution can be predicted for vanadium(II) complexes but such reactions are not as slow as those for the isoelectronic Crm ions. 

Vanadium(III) compounds are usually prepared from Vv or Viv by electrolytic reduction many complexes were prepared using VC13 as starting material. Usually, vanadium(III) complexes are unstable towards air or moisture and have to be prepared under an inert atmosphere. Many have octahedral coordination and their electronic spectra are typical of d2 ions with three spin-allowed d-d transitions ... 

Vanadium oxyfluorides also react with hydrogen peroxide to yield complex compounds.2 These are not so well defined as in the case of the peroxyfluorides of niobium and tantalum. 

Heteroalkenes, with iron, 6, 132 Heteroannulation, allylic benzylamines, 10, 156 Heteroarene chromium carbonyls, preparation and characteristics, 5, 260 Heteroarenes borylation, 10, 242 C—H functionalizations, 10, 127 as metal vapor synthesis milestone, 1, 237 with titanium, 4, 246 vanadium complexes, 5, 48 7]6-Heteroarenes, with platinum, 8, 664 Heteroaromatic compounds... 

Since the oxidative polymerization of diphenyl disulfide catalyzed by VO(acac)2 results in selective formation of thioether bonds without any oxygenated compounds such as sulfoxides and/or sulfones, it should be noted that H20 should be produced predominantly by the reduction of 02 catalyzed by the vanadium complex without the formation of partially reduced side products such as H202. 

There is little information available on the complexation of alcohols by live- or six-coordinate vanadium(V) compounds. Complexes of ethanolamine do form heteroligand products with alcohols [12], The formation constants for these materials are in the order of 0.2 to 0.5 M 1 and, therefore, are not very different from similar formation constants observed for alkoxovanadates. 

---