Vanadium methoxide

Vanadium Alkoxides. Except for the soHd methoxide, the lower vanadium alkoxides are slightly colored, yeUow, or yeUow-brown Hquids. They are easily hydroly2ed and decompose on heating above 100°C they darken. They are made from V20 or VOQ. -Vanadium alkoxides are used mostly in olefin polymeri2ation as catalysts also as hardeners and for coatings. 

The [VO]+ ion has been reacted with methylmethacrylate and the dimer of methylmethacrylate (157). Sequential addition of up to three methylmethacrylate molecules was observed, there were also several products involving bond cleavage such as loss of Me groups. Up to two molecules of the dimer of methylmethacrylate were added to [VO]+ and some final product ions involved the addition of other groups such as two methoxide groups. High coordination may be attained by vanadium in these product ions. 

Vanadium(V) alkoxides have been known since 1913,69 and in Table 2 we show some of the known alkoxides, the parent alcohol, and the nature of the complex in organic solvents and in aqueous solution. Alkoxides have been prepared from methanol, ethanol, isopropanol, t-butanol, silsequioxanes, cyclopentanol, cyclohexanol, norborneol, adamantanol, phenol, and other alcohols (see Table 2).70- 0 The simple complexes associate in organic solvents and dimerization in the presence of alkoxide is observed with the isopropanol complex.70 The more sterically hindred alcohols are less reactive and do not hydrolyze completely in the presence of small amounts of water.73 The first simple alkoxide to be structurally characterized was the methoxide complex (14) and the vanadium was found to be a six-coordinate dinuclear species however, the structure of this compound did not refine very well.91 This was the first report of the diamond core V—O—V—0 unit, albeit associated with two six-coordinate vanadium atoms. The diamond core V—O—V—O (11), which has since then been found to be a typical structural unit for these complexes, was distinctly asymmetric revealing a difference in the interactions between the two mononuclear parts of the molecule. The first monodentate alkoxide found to contain... 

The advantage of this method over the others described in the preceding sections is that the lithium chloride is soluble in methanol, making the separation of insoluble methoxides easily possible. The method was later extended by other workers for the preparation of methoxides of beryllium, " lanthanum,uranium, neptunium, vanadium, iron, ° and copper. ... 

In order to circumvent the problem of the use of selenium, analogous systems based on the use of sulphur compounds have been developed [85-88]. Aromatic nitro compounds can be reduced by CO in water/methanol media at 120-150 °C and 1-1.5 bar pressure [85, 86]. From nitrobenzene, aniline was obtained with selectivity over 97 % at 100 % PhN02 conversion. The reaction proceeds in the presence of a multicomponent catalyst consisting of a base (preferably a strong base such as sodium hydroxide or methoxide) and sulphur compounds. The ratio of catalytic effectiveness of sulphur compounds is as follows S CS2 H2S COS = 1 1.3 10 10. Vanadium(V) compounds can be added to improve selectivity in aniline formation. Aromatic dinitro derivatives undergo this reaction and selectivity to one of the two main products (phenylenediamine and nitroaniline) can be switched by the choice of reaction conditions. The main byproduct of the reaction of nitrobenzene is PhNHCOOMe [85, 86]. It has been shown that, under the catalytic conditions, methyl phenylcarbamate can be hydrolysed to afford aniline. More forcing conditions (up to 300 bar CO) have also been employed in order to increase the activity [87]. The same catalytic system has been used to reduce nitrophenols to the corresponding aminophenols [88]. 

---