Uranium alkoxides

The highest oxidation state (+6) appears not to be the most stable one for the alkoxides. Uranium hexaethoxide is easily converted into pentaethoxide on action of different reducing agents such as ethylmercaptane, diethylamine, and soon. Its interaction with uranium tetraethoxide leads to coproportionation [856] ... 

A variety of mixed ligand/alkoxide uranium(V) products are also isolable. Substitution compounds (U(0R)4L, U(0R)3L2, U(0R)2L3) were prepared from the reactions of U(OCH2CH3)5 with FlCl, /3-ketoesters (2,2,2,-trifiuoroaceto acetate, methyl acetate, ethyl acetate), acetyl chlorides... 

Uranium hexa-/ f/-butoxide is an exception and does not react with water (55). References 3 and 5 discuss chemical properties of alkoxides. In some cases hydrolysis is reversible, but usually it is not (23,56). 

Oxygen-Gontaining Organics. Neutral and anionic oxygen-containing organic molecules form a wide variety of complexes with uranium. Much work has focused on alkoxides (222), aryloxides and carboxylates complexes with alcohols, ethers, esters, ketones, aldehydes, ketoenolates, and carbamates are also well known. 

Alkoxide gels, 23 60 Alkoxide gels, in optical fiber manufacturing, 11 145 Alkoxide initiators, 14 259 Alkoxide ligands, thorium, 24 770 Alkoxides, 12 190 25 72-86 controlled hydrolysis of, 23 56 iron, 14 533 mixed-metal, 25 100 titanium, 25 82 uranium complexation with,... 

All the known tetraalkoxides are very easily hydrolyzed by water vapour and the uranium(IV) compounds oxidize rapidly in air, so their preparation must be carried out under nitrogen. Molecular weight determinations (M = Th, U) indicate a considerable degree of polymerization, approximately tetrameric in the case of Th(OR)4 with R = Pr or MeEtCH, but the molecular complexity decreases to about 3.4 for R = Bu, and with R = CEt3 and CMeEtPr the alkoxides are monomers in boiling benzene.653 The plutonium compound Pu(OCMeEt2)4 is volatile at 150 °C/0.05 torr, suggesting a low molecular complexity. 

U(OEt)5 is easily prepared by oxidation of U(OEt)4 by bromine in ethanol, followed by addition of the calculated quantity of sodium ethoxide, a reaction which yields181 only Np(OEt)4Br in the case of Np(OEt)4. U(OEt)s is commonly used as the starting material for the preparation of other uranium(V) alkoxides by alcohol exchange reactions. A comprehensive review of metal alkoxides includes a useful discussion of the uranium(V) compounds.182... 

The derivatives of the other new class—the alkoxide halides, MCORj HaU which are more reactive than the alkoxides themselves—were first described by Meerwein and Schmidt for magnesium and aluminium [1103, 1098]. An important input into the development of synthetic and physicochemical methods in the investigation of metal alkoxides was made by an outstanding meta-lorganic chemist H. Gilman [855, 856], who studied the derivatives of uranium in Los Alamos during the Manhattan Project. 

Only a few of rather numerous reactions of oxidation of alkoxides by oxygen, peroxides, halogens, and other compounds may be used for synthesis of M(OR) (with considerable yields). These reactions are known for uranium alkoxides [197, 856], such as... 

The alkoxides of actinides are rarely studied except the derivatives of uranium and thorium, as interest in the alkoxides of these 2 elements has increased by the hope to use them in the isotope-separation processes. The study of uranium alkoxides was initiated by groups led by Gilman and Bradley in the 1950s. The major part of this work is still carried out at the Nuclear Research Center at Los Alamos in the United States by the group of Sattelberger et al. [1671]. The detailed data on alkoxides ofuranium is provided in a number of... 

Nearly all the methods described in Chapter 2 have been applied for the preparation of uranium derivatives. The reaction of metallic uranium with alcohols in the presence of halogenes (method 1) doesn t lead, as it turned out, to homoleptic alkoxides, but is a facile route to alkoxide halides [79, 1669] ... 

Practically all the uranium alkoxides, excluding the polymeric derivatives of uranium (IV) and those of dioxouranium (VI), are rather highly soluble in both polar and nonpolar organic solvents (Table 12.20). Lowvalent ( IT-HI) derivatives are not volatile because of redox transformations that apparently accompany the heating. The volatility of alkoxoderivatives increases from tetrav-alent to hexavalent ones and in each homologous series with the increase in the size and ramification of the radical. 

An important feature of the alkoxide complexes containing uranium atoms in different oxidation states is their relative stability to redox transformations, U(cot)(OR)2, which can be formally considered as the complexes of uranium ( II ) should better be treated as the derivatives of uranium (IV), as the configuration of the alkene ligand is corresponding rather to the cot2+ anion. The latter acts also as a Jt-acceptor, which ensures the further stabilization of the molecule [64], Alkoxocomplexes of uranium (HI) can be easily transformed into the derivatives of uranium (IV) on action of different oxidants [79] ... 

The reaction with oxygen in contrast to that with nitrous oxide doesn t lead to the formation of oxoalkoxides, due probably to the intermediate formation of peroxocomplexes in this case. The reaction products are then alkoxides of uranium (IV) and uranium (IV) oxide ... 

It is of importance that uranium atoms remain electropositive even in rather high oxidation states. The M-OR bonds remain polar, and the molecules can act as the donors of alkoxide anions in the reactions with HC1 and organic halids, such as, for example, acylbromide [147] ... 

The stereochemistry of uranium alkoxides is very diverse, and it is possible to conclude that the geometry of the metal atom is independent on its oxidation state and the coordination numbers are in general lower than those observed for the inorganic compounds. In the series of monomeric U(IV) molecules — e.g., [U(OC6H3Bu 2-2,6)4] [1669], [UI2(OC6H3Bu 2-2,6)2THF] [79],... 

The preparation of monocyclo-octatetraenyl uranium(IV) alkoxide complexes from reaction of uranium cyclo-octatetraene precursors with alcohols has been reported [318]. A very unusual monomeric complex, U(OTeF5)6, which can be con-... 

UI3(THF)4 can easily be prepared in large scale, which makes easy the synthesis of U(III) complexes from it. According to Ref. 360, the use of solvated complexes of other uranium halides or uranium alkoxides involves some difficulties, in... 

The most important examples are the An02+ ions of U, Np, Pu, and Am (to be discussed later). Otherwise, there are only a few compounds such as the hexafluorides of U, Np, and Pu, as well as UC16, various oxohalides and oxohalide complexes (UOF4, UOFj, and UOCI5) and the uranium alkoxides, U(OR)6. 

Although they have been much less smdied than the range of alkoxides in the +4, +5, and +6 oxidation states, a number of amides of uranium(iv) have been made by salt-elimination reactions in solvents such as diethyl ether or THF, examples being ... 

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