Complexes of uranium

Allyl Complexes. Allyl complexes of uranium are known and are usually stabilized by cyclopentadienyl ligands. AEyl complexes can be accessed via the interaction of a uranium halide and an allyl grignard reagent. This synthetic method was utilized to obtain a rare example of a "naked" homoleptic allyl complex, U(T -C2H )4 [12701 -96-17, which decomposes at 0°C. Other examples, which are more stable than the homoleptic allyl complex have been synthesized, ie, U(allyl)2(OR)2 (R = alkyl), U(allyl)2X (X = halide), and U(allyl)(bipy)2. 

Heteroleptic complexes of uranium can be stabilized by the presence of the ancillary ligands however, the chemistry is dominated by methyl and benzyl ligands. Examples of these materials include UR4(dmpe) (R = alkyl, benzyl) and U(benzyl)4MgCl2. The former compounds coordinate "soft" chelating phosphine ligands, a rarity for the hard U(IV) atom. 

Phosphine complexes, osmium, 19 642 Phosphine coordination complexes, of uranium, 25 436 Phosphine derivatives, 19 28 Phosphine oxide(s), 11 495-496 19 66 predicted deviations from Raoult s law based on hydrogen-bonding interactions, 8 814t in salicylic acid manufacture, 22 8 Phosphine oxide diols/triols, 11 501 Phosphine selenides, 22 90 Phosphinic acid, 19 20, 54-55 Phosphinic anhydride, 11 499 Phosphinothricin acetyltransferase (PAT) proteins, 13 360 Phosphite esters, 19 20 Phosphites, in VDC polymer stabilization, 25 720... 

Diphenyl sulfoxide complexes of uranium(VI) have been reported (495) and a thorough infrared and conductivity study detailed (433), suggesting that the thiocyanate complexes of empirical formula [U02(R2S0)2(NCS)2] are in fact dimeric with bridging iV S-NCS ligands. 

The tris cyclopentadienide complex of uranium was first prepared by the direct reaction of uranium trichloride with a benzene suspension of potassium cyclopentadienide. More recently it has been prepared by the reduction of tetra-... 

In solution, it is possible to obtain what may be a complex of uranium(VI) fluoride and cyclohexanone, but under more drastic conditions uranium(VI) fluoride behaves as a Lewis acid and leads to condensation products, none of them fluorinated.13... 

Benzoylphenylhydroxylamine (17 R1 = R2 = Ph) forms complexes with V, Sn, Ti and Zr in 5 to 9 M HC1 but only that of vanadium is extractable into chloroform, permitting a selective determination of that element in chrome ores. A-Cinnamoyl-V-phenylhydroxylamine is even more sensitive. In less acid solutions solvent extractable complexes are formed with a number of other cations and, for example, an orange-red complex of uranium(VI) is extracted by V-benzoyl-iV-phenylhydroxylamine into chloroform.52... 

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] ... 

Berthet, J.C., Nierlich, M., Miquel, Y., Madic, C., Ephritikhine, M. 2005. Selective complexation of uranium(III) over lanthanide(IH) triflates by 2,2 6, 2"-terpy ridine. X-ray crystal structures of [MfOTf fterpy ] and [M(OTf)2(terpy)2(py)][OTf](M = Nd, Ce, U) and of polynuclear (x-oxo uranium(IV) complexes resulting from hydrolysis. Journal of the Chemical Society, Dalton Transactions 2 369-379. 

Schiff base and related complexes of uranium and thorium are widely described in recent literature and covered in a review [463]. Those of U(VI) have a practical use as catalytic organic oxidants [460] or as part of a polystyrene-supported chelating resin [464,465]. Among other Schiff base precursors, salicylaldehyde [466] and triethylenetetramine [464], 3-formylsalicylic acid and o-hydroxybenzylamine [465], or salicylaldehyde and l-amino-2-naphthol-4-sulfonic acid [467] were used. In the example of Schiff base complexes, kinetics of formation of U(VI) complexes and their pK values were studied [468]. 

A pure acetonitrile complex of uranium(IV) iodide cannot be isolated,8 but the salt [(CeHj As UI (red) can be readily prepared by the procedure described above in subsection 1, the pure halide being used instead of the acetonitrile complex. f( C H )4NJPaBr6 is extremely soluble in acetonitrile but it can be isolated in 100% yield by room-temperature evaporation of the solvent containing equimolar amounts of the component bromides. 

Terminal organoimido complexes of uranium(IV) are a more recent discovery. An Q -elimination reaction see a-Elimination) was designed for the synthesis of Cp 2U(=N-... 

Sorption in most soils attains a maximum when the neutral hydroxy complex of uranium is at a maximum. However, at pH 6 and above, and in the presence of high carbonate or hydroxide concentrations, uranium may form anionic complexes such as [U02(0H)4]. The mobility of anionic uranium complexes in soil is dependent upon the nature of the soil. For example, the decrease in sorption in soil with little anion-exchange capacity may result in increased mobility however, increased sorption in soil with high anion-exchange may result in decreased mobility (Allard et al. 1982 Ames et al. 1982 Brookins et al. 1993 Ho and Doern 1985 Hsi and Langmuir 1985 Tichnor 1994). 

Finally, we note the formation of complexes of uranium with tropolones with multiple stoichiometries and oxidation states. Letting Trop be tropolone and/or its 3-isopropyl derivative, these include U(Trop)4 Cl (0 < n < 4) (n = O, w = 1, 2, 3 ), U(Trop)5- Cl (n = 0, 1) U(Trop)5-U02(Trop)2 U02(Trop)+and U02(Trop)2(TropH) (but not the conjugate base). However, thermochemistry has rarely been of explicit interest. 

Examples of this analysis mode are presented in Fig. 5. The slope of the log D versus log[L],i plots for the cobalt(II)-8 M HCl and the Fe(III)-6 M HCl systems indicate the formation of CoClj and FeClj, respectively, as the predominant complexes in the Dowex 1-X8 phase. These results are believed to prove the reliability of this approach, the presence of these complexes in concentrated hydrochloric acid being well documented. The chloride complex of uranium(IV), UClj, v 4iose unique absorption spectrum is shown in Fig. 6 [11], in the HCl, HCIO4 (I = 10 M)... 

Sulfenamide. A homoleptic sulfenamido complex of uranium has been isolated from the reaction of Li(Bu NSPh) with UCI4 in the presence of PMe3 in toluene.The complex U(PhS=N-Bu )4 possesses two ry -coordinated sulfenamide ligands, and is nearly isostructural with the analogous zirconium complex. 

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