Vanadium derivatives

Maleic anhydride is commonly prepared by passing a mixture of benzene vapour and air over a catalyst (e.g. a vanadium derivative) at elevated temperatures (e.g. 450°C). It is a crystalline solid melting at 52.6°C (the acid melts at 130 C). 

Oxo-vanadium derivatives include numerous examples of Schiff base complexes, the importance of which is increasing in that they can act as insulin-enhancing agents.3 For instance, the vanadyl(IV) derivatives of TV.TV -ethylenebisCsalicylideneimine), [VO(salen)], A TV -disalicylidene-o-phenylenediamine, [VO(saloph)], and iV,Ar -ethylenebis(acetylaceto-natoimine), [VO(acen)], are shown in Scheme 1. 

The last vanadium derivative that we will consider is the N206 octacoordinated complex called Amavadin. It consists of a vanadium(IV) ion and two trideprotonated molecules of A -hydroxyl-2,2/-iminodipro-pionic acid (H3hidpa), [V(hidpa)2]2-. 

A collection of features for several peroxo species synthesized with this procedure can be found in two books that appeared about ten years ago" . With reference to composition and structure of peroxo vanadium derivatives, a meticulous compilation appeared in a 1998 book °. Several other metal peroxo species have been prepared until now and contain in the coordination sphere a plethora of ligands references will be also indicated in the appropriate following paragraphs. 

An inner-sphere hydrogen atom abstraction from the alcohol by a peroxo metal complex, thus forming a coordinated ketyl radical [(CH3)2—C —O—V(0)(00H)]" , has been proposed for the aerobic oxidation of alcohols catalyzed by peroxidic molybdenum and vanadium derivatives (Scheme 16). While in the case of Mo-catalyzed reaction the H2O2 produced is quantitatively converted to products (ketone and H2O), in the vanadium mediated process, hydrogen peroxide accumulates . In this latter case, the direct involvement of a vanadium monoperoxo species has been substantiated by ESI-MS data. 

Since the vanadium center of vanadocenes is electron-deficient, various vanadium derivatives are formed by the attack with PR3, CO, or unsaturated tt-donating hgands/ This reaction provides a useful synthetic method for the synthesis of jj -alkene complexes as described later. Thus formed Cp 2V(CO) (22) is converted to the cyano derivative (23, see Cyanide Complexes of the Transition Metals) on treatment with the isocyanide (Scheme 12). ( -C5Me5)2V is incubated with O2 at -78 °C to yield [(/u.-)] -C5Me503)V(0)]2 via oxygen insertion into the carbon-vanadium bond." ... 

Vanadium derivatives with empirical formulae A Vj,P ,0, where A is a monovalent cation and V may be present in more than one valency state, include... 

Lamellar or linear structures are also formed by various other metal ions, such as zinc, (268) manganese, (269) molybdenum, (270) and vanadium (271,272). Among these other solids, vanadium derivatives attracted significant attention due to their potential as industrial catalysts. The structures of the metal phospho-nates are similar to those of the corresponding phosphates, in a manner similar to the zirconium phosphate/phosphonates. Polymerization of phenylphosphonate, for example, with Mo(IV) resulted in a linear double-stranded structure where the phenyl groups are positioned on the outside of the linear structure (273). These othCT metal derivatives are bound to yield many future investigations regarding the fundamental and applied chemistry of layered mataials. 

Information on the carbonyl chemistry of niobium and tantalum is, to date, very meager. The main difficulty appears to be the reduction of the usual pentavalent derivatives of these metals to the very low formal oxidation states of metal carbonyl derivatives. Nevertheless, the yellow anions [M(C0)6] (M = Nb, Ta) have been obtained by a method analogous to, but more difficult than, one of the preparations of the [VCCO) ]" anion. The method involves reduction of the pentachlorides with sodium metal in diglyme in the presence of high pressures of carbon monoxide (63). The niobium and tantalum derivatives are much more air-sensitive than the analogous vanadium derivative. The niobium derivative has not yet been obtained analytically pure (63). No chemistry of the [Nb(CO)J and the [Ta(CO)6] ions has been reported, even conversion to the neutral carbonyl derivatives [M(CO) (M = Nb or Ta = 1 or 2) or to the carbonyl hydride derivatives HM(CO)6 (M = Nb, Ta) still presenting unsolved problems. 

Uranium from weathered granites and vanadium derived from greenstones are present in the groundwater and valley-fill sediments. Uranium, vanadium and potassium concentrate downstream by evaporation and combine in the oxidizing environment to form carnotite, which fills cavities and fractures in the calcrete. Carnotite also forms in a clay-quartz unit beneath the calcrete. Resources at Yeelirrie are estimated at 47000 ton UgOg at grades of 0.05-0.10%. 

The reaction achieves completeness, when the alkoxides thus formed display quite considerable resistance to hydrolysis and can then be purified by some efficient technique (distillation for vanadium derivatives and recrystaUization for the diolates). 

---