Uranium complex

Tetrakis-Cp uranium complexes are readily prepared via metathesis of UCl and KCp in refluxing benzene. These complexes are a relatively rare example of a pseudotetrahedral complex with four Tj -Cp rings, (rj-ring) (25). The Cp derivative has been shown to react with CO and CO2 to give acyl and carboxylato complexes. This complex also reacts with alkyl haUdes to afford the U(IV) complex, Cp UX (X = halide). 

Hydrocarbyl Complexes. Stable homoleptic and heteroleptic uranium hydrocarbyl complexes have been synthesized. Unlike the thorium analogues, uranium alkyl complexes are generally thermally unstable due to P-hydride elimination or reductive elimination processes. A rare example of a homoleptic uranium complex is U(CH(Si(CH2)3)2)3, the first stable U(I11) homoleptic complex to have been isolated. A stmctural study indicated a triganol... 

Bimetallic Complexes. There are two types of bimetaUic organometaUic uranium complexes, those with, and those without metal—metal interactions. Examples of species containing metal—metal bonds are complexes with Mo, W, Ee, or Ru carbonyl fragments. Examples of these include (Ti-ring)3U( a-OC)(M(CO)2(Tl-fing)) M = Mo, W), [N(Si(CH3)3)2]3U( a-OC) M(CO)2(Tl-fing) (M = Mo, W), and (Ti-ring)3U(CpM(CO)2) (M = Fe, Ru). 

Uranium. tetrathiocyanatotetrakis[tris-(dimethylamino)phosphine oxide]-structure, 1.87 Uranium carbide nuclear fuels dissolution, 6, 928 Uranium complexes, 3,1131-1215 carbamic acid... 

In dealing with solvent extraction as applied to uranium, it may at first be pointed out that uranium can exist in aqueous solution either as a neutral complex, a complex anion, or a cation. The organic solvents used in solvent extraction can accordingly be divided into three classes, according to the type of uranium complex extracted. 

Uranium complexes analogous to these compounds were also described, but with the cot (cyclooctatetraene dianion) ligand rather than the Cp or Cp ones. Both the dianionic U(IV) [(cot)U(dddt)2]2 [47] and monoanionic U(V) [(cot)U(dddt)2] [48] complexes were isolated and structurally characterized (Fig. 5). Spectacular distortions of the US2C2 metallacycles were rationalized on the basis of DFT calculations, which reproduced the spectacular folding of the endo US2C2 metalla-cycle when the dianionic species undergoes an oxidation. 

At variance with the d1 V or Nb complexes described above, the uranium complexes owe their paramagnetism to 5/-electrons. Although these / orbitals, and particularly the 5/in the actinides when compared with the 4/in the lanthanides, interact with the dithiolene orbitals to lead to strong distortions of the US2C2 metallacycles (see Fig. 5) [35, 36, 47, 48], the SOMOs themselves are essentially... 

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,... 

Aryloxide ligands, thorium, 24 770 Aryloxides, uranium complexation with, 25 436-437... 

Bilinear chemometrics methods, 6 39-57 Billet products, titanium, 24 858 Bill of Material, 15 460, 470 Bills of lading, 25 330 Bimetal complexes, 16 88 Bimetallic deactivation processes, 16 93-94 Bimetallic fluorides, 15 396 Bimetallic metal nitrides, 17 199 Bimetallic organometallic uranium complexes, 25 442 Bimetallic organometallic thorium complexes, 24 773-774... 

Heterojunction with intrinsic thin layer (HIT) photovoltaic cell, 23 46-47 Heteroleptic uranium complexes, 25 441 Heterologous promoters, 22 453 Heteronano interface (HNI), 23 838 Heteronium bromide, 4 359t Heteronuclear metal carbonyls, synthesis of, 26 69-71... 

Substituent effects, 9 510 Substituted alkylhydrazines, 13 572-573 Substituted amide waxes, 26 221 Substituted cyclopentadienyl uranium complexes, 25 440-441 Substituted cyclopentadienyl (Cp)... 

Triscarbonato uranium(VI) solids, 25 432 Tris-Cp uranium complexes, 25 440 2,4,6-Tris(dimethylaminomethyl)phenol (TDMAMP), 10 412... 

Reduction of nitrobenzene (Grant and Streitwieser 1978, Todres et al. 1985) and 4-methoxy-nitrobenzene (Todres et al. 1985) by uranium, thorium, and lanthanum-di(cyclooctatetraene) complexes leads to azo compounds. Scheme 1.8 illustrates these reductive reactions using the di(cyclooctatetraene)-uranium complex as an example. 

The uranium tends to concentrate in the fine fractions of soils in which clays can adsorb uranium complex compounds [U02] " transported from uranium deposits. 

Recently, a uranium complex with p3Trol anion has been prepared and characterized by proton magnetic resonance spectroscopy 90). 

A second example of a bis cyclopentadienyl uranium complex has resulted from the use of a bidentate, bridged bis(cyclopendadienyl) ligand to avoid further reaction to a tris species. It is prepared by the addition of the dianion of bis(cyclo-pentadienyl)methane to uranium tetrachloride in THE to give [CH2( — 5114)2]... 

The first S5m.thetic ventures into actinide and lanthanide organometalhc chemistry were attempted during World War II and were motivated by the need for stable, volatile uranium complexes in the uranium gaseous diffusion process. It soon became apparent that the homoalkyl complexes (MR4) of uranium were extremely unstable and at best could exist only as transient intermediates at low temperatures [128). With the isolation of the tricyclopentadienides of the lanthanides in 1954, the focus of /-transition metal organometaUic chemistry shifted to the n-carbocychc complexes and has remained unchanged until the recent isolation of stable alkyls and aryls of both the lanthanides and actinides. 

For example, in 1963 the photochemistry of magnesium phthalocyanine with coordinated uranium cations was studied in pyridine and ethanol and indicated the occurrence of PET to the uranium complex . A rapid photoinduced electron transfer (2-20 ps) followed by an ultrafast charge recombination was shown for various zinc and magnesium porphyrins linked to a platinum terpyridine acetylide complex . The results indicated the electronic interactions between the porphyrin subunit and the platinum complex, and underscored the potential of the linking para-phenylene bisacetylene bridge to mediate a rapid electron transfer over a long donor-acceptor distance. 

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