Amines uranium complexes

A number of actinide complexes have been investigated with respect to their catalytic activity in the intermolecular hydroamination of terminal alkynes with primary ahphatic and aromatic amines [98, 206-209]. Secondary amines generally do not react and the reaction is believed to proceed via an metal-imido species similar to that of group 4 metal complexes. The reaction of Cp 2UMc2 with sterically less-demanding aliphatic amines leads exclusively to the anti-Markovnikov adduct in form of the -imine (31) [207] however, sterically more demanding amines, e.g., t-BuNH2, result in exclusive alkyne dimerization. The ferrocene-diamido uranium complex 12 (Fig. 4) catalyzes the addition of aromatic amines very efficiently (32) [98]. 

Aromatic amines form addition compounds and complexes with many inorganic substances, such as ziac chloride, copper chloride, uranium tetrachloride, or boron trifluoride. Various metals react with the amino group to form metal anilides and hydrochloric, sulfuric, or phosphoric acid salts of aniline are important intermediates in the dye industry. 

The extraction of metals by liquid amines has been widely investigated and depends on the formation of anionic complexes of the metals in aqueous solution. Such applications are illustrated by the use of Amberlite LA.l for extraction of zirconium and hafnium from hydrochloric acid solutions, and the use of liquid amines for extraction of uranium from sulphuric acid solutions.42,43... 

Table 7 Some Amine Complexes of Thorium(IV) and Uranium(IV) Compounds...

Concentration/purification by solvent extraction usually involves four steps (a) extraction of uranium from the leach liquor in a solvent, (b) scrubbing to remove impurities from the solvent, (c) stripping to remove uranium from the solvent, and (d) regeneration of the solvent. The solvent phase in solvent extraction will contain the extractant that complexes uranium to make it soluble in the organic phase, a diluent, an inexpensive material to dilute the extractant, and a modifier to improve the solubility of the extractant in the diluent. Typical extractants are amines with isode-canol acting as a modifier to improve the amine solubility in a diluent such as kerosene. The typical chemistry of the extraction would involve the reactions... 

Some authors consider that the extracted complex is best formulated as an adduct, such as [(RjNH)2S04]2, U02S04(H20)3, which is the stoichiometry suggested by Sato on the basis of the analysis of solutions of tri- -octylamine saturated with uranium.204 Further studies of the extraction of uranium from sulfate media by amine salts have been reviewed by Cattrall and... 

The reactions of ligand exchange have frequently been applied to synthesize chelates with the coordination unit containing N,0-donor centers. The complexes of titanium [280], thorium, and uranium [281] tetrachlorides with fe(salicylidene)alkylene-amines, obtained in THF solution, are evidently formed through THF complexes of the type MX (THF). An example of such syntheses is the transformation (3.107) [280] ... 

Citric acid forms a mixed-metal complex with iron and uranium, similar to the U-citrate complex the Fe-U citrate complex is inert to biodegradation [333a]. A series of publications are dedicated to uranium peroxo complexes with various coligands tri- and quadridentate Schiff bases [334,335], amines, or amino-... 

The structures obtained by x-ray and neutron diffraction analysis of compound [U N(SiMe3)2 N(SiMe3)(SiMe2CF[2B(C2B(C6F5)3) ] reveal the electron deficiency of the uranium atom to be effectively compensated by the formation of multicenter bonds between the U atom and Si — CH2 units of the amido ligands the x-ray structure of [U C(Ph)(NSiMe3)2 2 r3-BH4 2] proves unequivocally the -coordination of the BH4 units [444]. The structure of a rare uranium (III) complex with a tripodal aromatic amine tm[(2,2 -bipyridin-6-yl)mcthyl]amine was reported [445]. 

Amine Extraction. Extraction of uranium (VI) and plutonium (VI) from acetic acid with tri-iso-octylamine in xylene has been studied previously by Moore (JJ), who suggests that the extracted species is the triacetate ion. The spectra in Figure 1 show this is not the predominate species extracted into TOA-xylene solutions (9). Comparing the spectrum of this extracted uranium with the spectra of pure tetraacetate and triacetate complexes in Figure 3 shows that the TOA-xylene extracts a mixture of these ions that is largely tetraacetate uranyl complex. 

Moore has shown that thet extractability of U(VI) by 5% tri-wo-octylamine in xylene passes through a maximum at about 0.5N aqueous acetic acid, and it continues to decrease to 14N acid. Our spectral measurements show that the species extracted by TOA in either xylene or chloroform are nearly independent of aqueous acid concentration, although the triacetate complex seems to be slightly favored by increase of acid to ION. There is also a small increase in the percentage of the triacetate ion extracted when uranium to amine ratio is increased. 

Such experiments show that oxalate, tartrate, and citrate give fairly strong complexes, and indeed these mixtures do not suffer quite such rapid oxidation as the other systems (57, 70). Stability constants for the complexing of U(III) by acetate, 2-hydroxy-2-methylpropionate, nitriloacetate, trans-cyclohexyl-1,2-diaminotetraacetate, ethylenedi-amine tetraacetate, and diethylenetriamine pentaacetate have been reported, but no pure compounds have been isolated (71). Thiocyanate also accelerates oxidation of the uranium, but the blue complex that is formed can be extracted with triethyl phosphate, tributyl phosphate, or better, trioctyl phosphine oxide the organic extract decomposes only slowly (45, 72). 

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