Active uranium hydrocarbon solvents

This approach frequently leads to the most active metals as the relatively short reduction times at low temperatures leads to reduced sintering of the metal particles and hence higher reactivity. Fujita, et aL(62) have recently shown that lithium naphthalide in tqluepe can be prepared by sonicating lithium, naphthalene, and N, N, N, N-tetramethylethylene-diamine (TMEDA) in toluene. This allows reductions of metal salts in hydrocarbon solvents. This proved to be especially beneficial with cadmium(49). An extension of this approach is to use the solid dilithium salt of the dianion of naphthalene. Use of this reducing agent in a hydrocarbon solvent is essential in the preparation of highly reactive uranium(54). This will be discussed in detail below. 

In order to eliminate competing reaction with the solvent, a method for generating active uranium in hydrocarbon solvents was desired. Thus a hydrocarbon soluble reducing agent [(TMEDA)Li ]9 [Nap] (Nap=naphthalene) was prepared. This complex has previously been maae from 1,4-dihydro-naphthalene(llO). We have prepared this complex from lithium, naphthalene and TMEDA in a convenient reaction which is amenable to large scale synthesis. 

Since 1972, we have published many reports describing convenient methods for the generation of highly reactive metal powders and their use in organic as well as organometallic synthesis [28-34]. Most of the active metals prepared by our group have been prepared in ethereal solvents [35]. Our initial report on the preparation of active uranium (I) employed 1,2-dimethoxyethane (DME) as a solvent (Scheme 13.1) [31]. We have since developed a method for preparing active uranium (3) in hydrocarbon solvents, which leads to a much cleaner and more controllable chemistry compared to 1 [34, 36]. 

Active thorium has been prepared in a manner analogous to that of active uranium. Active thorium reacts with DME, as does active uranium I. When benzophenone is reacted with active thorium in refluxing DME, the product mixture contains TPE and TPA in low yield (< 10%), as well as many other coupled products containing solvent fragments. The reactivity of active thorium with aromatic ketones in hydrocarbon solvents is similar to that of active uranium, although the yields tend to be lower (3 days in refluxing xylenes 11%... 

The following describes a typical preparation of active uranium in hydrocarbon solvents. In the dry box, UCI4 (0.5020g, 1.322mmol) and 2 (1.0143g, 2.7086 mmol) were placed in a two-necked 50 ml flask equipped with a Teflon-clad stir bar, vacuum adapter, and septum. On the vacuum line, freshly distilled solvent (20 ml) was added and stirring started. After Ih of stirring at room temperature, the active uranium was ready for use. 

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