Uranium trivalent

Fluoroalkyl copper compounds, 17 143, 144 a-Fluoroalkylidinehydrazines, 33 167 2-Fluoroalky 1 -2 phospha-1,3-dialky 1 -1,3-diaze-tidinones, synthesis of, 14 87 Fluoroanions, trivalent, uranium, 34 94—95 Fluoroantimony compounds, 7 17 Huoroaryl copper compounds, 17 143, 144 Fluoroberyllates anhydrous, 14 267-276 aqueous chemistry of, 14 274-278 glasses, 14 265-267 preparation and properties of, 14 265-267... 

Halo-carboxylic acids, reduction by trivalent uranium, 34 80... 

Uranium exists in the +3, +4, +5, and +6 oxidation states. The +5 state dispropor-tionates to the +4 and +6 states and is of little importance. Trivalent uranium reduces water and therefore there is no stable aqueous chemistry of U3+ although compounds do exist. 

Trivalent Uranium A Versatile Species for Molecular Activation... 

There are three main characteristics of trivalent uranium that affect its chemical behavior. One consists of its large atomic dimensions, as witnessed by a particularly extended van der Waals radius (1.86 A) (8). The large atomic... 

TRIVALENT URANIUM A VERSATILE SPECIES FOR MOLECULAR ACTIVATION 323... 

Molecular Activation. The strong reducing power of trivalent uranium enables interaction with both inert and less inert functions such as sp3 C—H bond, N2, and H20 displaying a variety of transformations and unusual bonding features. 

Coordination Chemistry. The coordination chemistry of trivalent uranium is certainly characterized by the large atomic dimensions as appearing in series of compounds featuring C-, N-, S-, and O-donor based ligand complexes. 

Although the trivalent uranium species of the tetrapyrrolide polyanions display a very high reactivity, no evidence was found for the ability to interact with N2. However, the reduction of the trivalent [ [(—CH2 )5]4-calix[4]tetrapy-rrole U(dme)][K (dme)] with [K-(naphthalenide)] in DME afforded N2cleavage with formation of the mixed-valenceU(IV)-U(V) nitride below (Scheme 13) (36). The highly reactive species that performs the N2 cleavage in this case was not identified since reactions carried out under an Ar atmosphere promoted solvent deoxygenation, as well as depolymerization of polysilanol. 

The presence of two rather than three Cp rings around the trivalent uranium centers seems to provide an optimum stability to the complex. The synthesis of the Cp UI2(thf)3 and Cp 2UI(thf) was achieved in high yield upon treatment of UI3(thf)4 with the appropriate amount of Cp K (Scheme 17). Further functionalization of Cp UI2(thf)3 was obtained via a metathetic reaction with silazanate. The crystal structure of the resulting Cp U[N(SiMe3)2]2 showed the presence of agostic interactions between the U center and the methyl groups of the silazanate moiety (47). 

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