Of samarium metal

The oxide, the precursor to the metal/alloy, is currently available to the extent of about 150-200 tons per year and output may conceivably be doubled by 1985. Even so, when expressed in terms of samarium metal this quantity is relatively small, hence it is desirable to optimise the available resources by whatever means are possible. In Table II we illustrate one solution to the problem, namely the production of alloys containing much greater quantities of mischmetal. 

Reduction of multiple bonds with samarium diiodide has been reviewed. Chemo-and stereo-selective reduction of various compounds such as conjugated alkenes, c/,/3-unsaturated carboxylic acids, activated alkynes, carbonyl, azides, nitriles, and nitro compounds, under mild conditions, has been discussed. Recent developments in the use of samarium metal in this field have also been discussed.381... 

Exposure of the dioxanobornane 1055 to samarium diiodide in the presence of samarium metal at low temperature leads to the formation of a mixture of the tetrahydropyran-4-one 1056 and the ring opened product 1057. Treatment of this mixture with tosic acid leads to a single tetrahydropyran-4-one product (Scheme 269) <2004OL3735>. 

In 1992, Ishii reported the generation of a Sml2 equivalent that displayed similar reactivity to Sml2 by treatment of samarium metal with TMSC1 and Nal.4... 

In recent years, exposing the preparation of the reagent from samarium metal and an oxidant to different stimuli has led to significant improvements in reaction time. Concellon utilized the sonication of samarium metal and iodoform at room temperature to give a solution of Sml2 in THF in approximately 5 min (Scheme 2.3).5 This approach was also used by Flowers to synthesise other Sm(II) species.6 It was also reported that using different oxidants, such as 1,2-diiodoethane, diiodomethane and iodine, works just as well with this technique.5... 

The exploration of Lnl2(THF) c, in particular, Sml2(THF)4, which is prepared by the reaction of samarium metal with ICH2CH2I in THF [96], or the reaction of iodine with an excess of samarium metal in THF, provides appropriate starting materials for divalent organometallic complexes (Equation 8.29). 

Samarium diiodide is very conveniently prepared by oxidation of samarium metal with organic di-halides or with iodine (equations 10-12). Deep blue solutions of SmI (0.1 M in THF) are generated in virtually quantitative yields by these processes. This salt can be stored as a solution in THF for long periods when it is kept over a small amount of samarium metal. Tetrahydrofuran solutions of SmI are commercially available as well. If desired, the solvent may be removed to provide Sml2-(THF)n as a powder. For synthetic purposes, Smh is typically generated and utilized in situ. 

The dimeric mono(cyclooctatetraenyl)lanthanide chlorides [(COT)Ln(/r-Cl)(THF)2]2 are long known and still represent the most useful precursors in (COT)Ln chemistry. A recently reported alternative preparation of the Sm derivative involves the reaction of samarium metal with COT in THF in the presence of a small amount of I IgCL. The molecular structure of [(COT)Sm(/i-CI)(TT 11 )2]2 has been determined.805,806 Iodo-(cyclooctatetraenyl)lanthanide iodides of the type (COT)Lnl(TIIF) (Ln = La, Ce, Pr, n = 3 Ln = Nd, n = 2 Ln = Sm, n l) are readily accessible in a one-pot reaction of metallic lanthanides with COT in the presence of an equimolar amount of iodine. Bromo- and chloro-bridged binuclear complexes of samarium, [(COT)Sm(/.t-X)(THF )2]2 (X = Br, Cl), were also prepared by the reaction of samarium metal with COT in the presence of 1,2-dibromoethane or Ph3PCl2, respectively.807 Alternatively, the iodo complexes (COT)LnI(THF)3 (Ln = Nd, Sm) can be synthesized directly from the lanthanide triiodides and K2COT. The molecular structure of (COT)Ndl(THF)3 has been determined by X-ray diffraction.808 A clean preparation of the monomeric half-sandwich complex (GOT)TmI(THF)2 involves treatment of Tml2 with equimolar amounts of COT in THF at room temperature (Scheme 227). The product was isolated as red crystals in 75% yield.628... 

Handling, Storage, and Precautions is air sensitive and should be handled under an inert atmosphere. S111I2 may be stored over THE for long periods when it is kept over a small amount of samarium metal. 

In the presence of samarium metal-trimethylsilyl chloride, (Z)-allyl selenides 370 were stereoselectively afforded by a one-pot reaction of diselenides with MBH adduct under mild eonditions. Presumably, the diselenides are cleaved by the Sm-TMSCI system to form selenide anions, which then undergo S 2 substitution of MBH adduets to produce the corresponding (Z)-allyl selenides 370 in high yields (Scheme 3.165). ... 

A bis(pentamethylcyclopentadienyl) samarium(II) complex containing two tetra-hydrofuranes was made by W.J. Evans et al. (1981a) by vaporization of samarium metal into a mixture of pentamethylcyclopentadiene in hexane at — 120°C. From the reaction mixture a purple crystalline compound could be isolated and characterized by an X-ray structural analysis (fig. 45, table 41), as well as by H and C NMR spectra. 

The obstinate ones Sm, Eu and Yb — reduction of the oxide When all of the rare earth oxides became available in large quantities via ion-exchange separation techniques, samarium was included in metal preparation studies. While there had been some earlier reports of samarium metal being prepared (Klemm and Bommer 1937, Trombe 1938), the absence of general descriptions of the properties of the metal suggested that it had not been obtained. In later studies, both the trichloride and the trifluoride (of samarium) were treated with calcium just as the other rare earth metals (Keller et al. 1945, Spedding et al. 

The major breakthrough occurred in 1953 when the Ames Laboratory team (Daane et al. 1953) reported the preparation of samarium, europium and ytterbium in high purity and high yields by the reduction of their oxides with lanthanum metal in a vacuum. With the preparation of samarium metal, finally, 126 years after the first rare earth element was reduced to its metallic state, all of the naturally occurring rare earths were now available in their elemental state in sufficient quantity and purity to measure their physical and chemical properties. The success of this reaction is due to the low vapor pressure of lanthanum and the extremely high vapor pressures of samarium, europium and ytterbium (Daane 1951, 1961, Habermann and Daane 1961). It is interesting to note that this same technique has been the method of choice for the preparation of some transplutonium metals (Cunningham 1964). 

The metallothermic reduction of SmCls designed for the preparation of samarium metal with an (apparently) insufficient quantity of sodium, resulting in the formation of... 

Experiments have shown that there are divalent atoms present at the surface layer of samarium metal (Wertheim and Crecelius 1978, Allen et al. 1978). Therefore, in the BIS experiments there should also be some spectral contribution from a transition to a monovalent samarium ion at the surface. From the complete screening model, the position of the f level (again using eq. (8) and estimated atomic spectroscopic data) should be at about 4.1 + 0.4 eV above the Fermi energy. 

The A//298 WrtS calculated to be 196.23 1.26 kjmol , and AS298 was derived to be 80.54 JK mol . The estimated boiling point for the metal is 1745 K. Nugent et al. [81] had estimated the heat of sublimation to be 163 kJ mol and David et al. [82] had predicted a value of 197 kJmol . The vapor pressure of californium metal is intermediate between that of samarium metal (trivalent) and of europium metal (divalent) [80]. The data show that the californium metal was clearly trivalent up to 1026 K, and that it is one of the most volatile actinide metals. Its high volatility precludes bulk vaporization studies above 1073 K by the Knudsen technique. No evidence by mass spectrometry was obtained in this latter work for the presence of CfO. 

To avoid the problem noted above, Ruder and coworkers utilized acetonitrile as the solvent milieu for the Sml2 mediated coupling of acid halides with ketones. The reductant was prepared in acetonitrile by the reaction of samarium metal and diiodoethane. The resultant solution was green in color. While the reaction of acid halides and ketones was shown to result in the formation of iodoesters (eq. (61)) using THF, in acetonitrile, this side reaction is suppressed and higher yields of of-hydroxy ketones were obtained (table 12). 

Tetrahydropyran (THP) has also been utilized as solvent in the preparation of Sml2 (Namy et al., 1994). The major benefit of utilizing THP in place of THF is the complete absence of by-products arising from ring opening of the solvent (table 14). A solution of Sml2 in THP is readily prepared by the reaction of samarium metal and 1,2-diiodoethane. Its application in the coupling of acid chlorides with carbonyl substrates has been reported (eq. (67)). 

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