Uranium alkyls

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... 

Table 12.5 Thorium and uranium alkyl/hydride complexes on various supports, including respective C CP MAS NMR data and assignments (5 in ppm) .

Question 13.1 Suggest why, at the time of the Manhattan project in the 1940s, Gilman attempted the synthesis of simple uranium alkyls and aryls as vehicles for isotope separation. Answer 13.1 At that time, few d-block alkyls and aryls were known. Gilman would have reasoned that by analogy with compounds of the Group IV elements like carbon and silicon, uranium(iv) alkyls and aryls might have simple molecular structures and thus be volatile. 

The analogous uranium(III) compounds also show unusual reactivity patterns. For example, addition of COT to (Cp )3U yields a mixed metallocene dimer (18) bridged by a COT ligand in this reaction, the (Cp )3U complex has effectively acted as a formal three-electron reductant (equation 3)." A variety of substituted (Cp )3U complexes form adducts with CO and CNR (isocyanides) - these are rare examples of actinide metals with r-acidic ligands." Paramagnetic uranium alkyl complexes are active in a range of catalytic processes." ... 

Marks and co-workers (10, 10a) also studied the photochemistry of uranium alkyls in toluene solution at ambient (10°C) and low (-196°C) temperatures. As with the thorium alkyls, mixtures of the corresponding alkane and alkene were produced in near quantitative yield [e.g., Eq. (6)]. 

As the above results indicate, the photochemistry of these uranium-alkyl complexes is not fully resolved. The olefin formation during Marks s siudy of UCP3R in toluene solution suggests that photoinduced /3-hydride elimination occurs to some extent, presumably via a mechanism similar to that of Scheme 1. However, the other data appear to indicate a predominant radical mechanism via photoinduced M—R bond homolysis. 

The first actinide organometallic complex, red-brown (C5H5)3UC1, was prepared and characterized by Reynolds and Wilkinson in 1956 or shortly after the discovery of ferrocene see Ferrocene, (C5H5)2pe. However, it was not until the preparation and structural characterization of bis(cyclooctatetraenyl)uranium, (C8H8)2U ( uranocene , see Uranocene) in 1968 and the isolation and characterization of uranium alkyls see Alkyl Complexes) in 1973 that the field developed momentum. The purpose of this chapter is to provide an overview of organoactinide chemistry that reflects historical as well as recent developments and achievements in the field it is not meant to be an exhaustive review of the primary literature. More detailed discussion, background material, and extensive references to the literature can be found in several excellent reviews. 

Prior to and during the Manhattan Project, considerable eflFort was directed toward the synthesis of volatile uranium alkyl compounds such as U( 2115)4 for use in isotope separation. These attempts were unsuccessful (8, 9) and it was assumed that the uranium alkyl bond was intrinsically unstable. Thus, for several decades the nature of the uranium-to-carbon linkage remained unexplored, and there was even some question as to whether such bonding could take place. 

Dormand, Elbouadili, and Moise [31] have also studied the insertion chemistry of pentamethylcyclopentadlenyl uranium alkyls with isocyanides (eq.(37). As for the aforementioned Cp3UR series, the products have... 

The photochemistry of U(C H ) R (R=CH, n-C H ) derivatives was first described by Giannotti, Marquette-Ellis, and Fischer. They observed that photolysis of uranium alkyl complexes in toluene and THF solutions at 60 C apparently results in the cleavage of the alkyl-uranium bonds and in the formation of a (C H ) U THF adduct ... 

Matson EM, Forrest WP, Fanwick PE, Bart SC. Use of alkylsodium reagents for the synthesis oftrivalent uranium alkyl complexes. Organometallics. 2012 31 4467-4473. 

Trivalent uranium alkyls can be synthesized via the following approach [48, 49] ... 

Duhovic S, Monreal MJ, Diaconescu PL. Reactions of aromatic heterocycles with uranium alkyl complexes. Inorg Chem. 2010 49 7165-7169. 

Monreal MJ, Diaconescu PL. A weak interaction between iron and uranium in uranium alkyl complexes supported by ferrocene diamide ligands. Organometallics. 2008 27 1702-1706. 

Uranium.—Uranium alkyls of the type [U(Bu )(A -C6H6)3] are thermally stable and appear to resist jS-elimination and probably decompose by a free-radical pathway. Decomposition of [U(Bu")(A -C5H5)3] in [ Hgltoluene produces butane with only about 5 % incorporation of deuterium, suggesting that hydrogen abstraction occurs principally within a solvent cage from the cyclopentadienyl rings. ... 

---