Samarium preparation

Various types of alkylpytroles are prepared under mild conditions by reacting nitroalkenes with Imines in the presence of SmfOi-Pri- fEq. 10.11. Thus, the Grob-Camenish type reacdon is accelerated by samarium catalysts. 

While ytterbium(II) benzamidinate complexes have been known for many years/ the synthesis of the first divalent samarium bis(amidinate) required the use of a sterically hindered amidinate ligand, [HC(NDipp)2l (Dipp = C6H3Pr2-2,6)/ As illustrated in Scheme 54, the dark green compound Sm(DippForm)2(THF)2 (DippForm = [HC(NDipp)2] ) can be prepared by three different synthetic routes. Structural data indicated that hexacoordinated... 

Evans and Wu have prepared complexes derived from PyBOx ligands and samarium or gadolinium triflates that were efficient for the Diels-Alder reaction between various quinones and dienes [102] (see Scheme 38 for an example). 

Calciothermic reduction of samarium oxide, in the presence of cobalt powder, yields samarium-cobalt alloys in the powder form. The process is popularly known as reduction diffusion. Samarium oxide, mixed with cobalt powder and calcium hydride powder or calcium particles, is heated at 1200 °C under 1 atm hydrogen pressure to produce the alloys. Cobalt oxide sometimes partly replaces the cobalt metal in the charge for alloy preparation. This presents no difficulty because calcium can easily reduce cobalt oxide. A pelletized mixture of oxides of samarium and cobalt, cobalt and calcium, with the components taken in stoichiometric quantities, is heated at 1100-1200 °C in vacuum for 2 to 3 h. This process is called coreduction. In reduction diffusion as well as in coreduction, the metals samarium and/or cobalt form by reduction rather quickly but they need time to form the alloy by diffusion, which warrants holding the charge at the reaction temperature for 4 to 5 h. The yield of alloy in these processes ranges from 97 to 99%. Reduction diffusion is the method by which most of the 500 to 600 t of the magnetic samarium-cobalt alloy (SmCOs) are produced every year. 

All the rare earth metals except samarium, europium, and ytterbium can be prepared in a pure form by reducing their trifluorides with calcium. Magnesium fluoride is less stable than the rare earth fluorides and so magnesium does not figure as a reductant. Lithium forms a fluoride which is stabler than some of the rare earth fluorides and thus finds some use as a reductant. 

Low-valent lanthanides represented by Sm(II) compounds induce one-electron reduction. Recycling of the Sm(II) species is first performed by electrochemical reduction of the Sm(III) species [32], In one-component cell electrolysis, the use of sacrificial anodes of Mg or A1 allows the samarium-catalyzed pinacol coupling. Samarium alkoxides are involved in the transmet-allation reaction of Sm(III)/Mg(II), liberating the Sm(III) species followed by further electrochemical reduction to re-enter the catalytic cycle. The Mg(II) ion is formed in situ by anodic oxidation. SmCl3 can be used in DMF or NMP as a catalyst precursor without the preparation of air- and water-sensitive Sm(II) derivatives such as Sml2 or Cp2Sm. 

The rare earth oxides of lanthanum, samarium and gadolinium were converted into soluble nitrate salts by dissolving them in the minimum amount of concentrated nitric acid. Then two sets were prepared by adding 2.0 ml of aqueous solution of La(N03)3.6H20 [0.2 M] and 0.01 ml of (n-BuO)4Ti to 25 ml of aqueous solution of Cu(N03)2 [1.0 M]. Similarly, two sets were prepared with Co(N03)3. Same procedures were followed for Sm(N03)3 [0.2 M] and Gd(N03)3 [0.2 M], One set of all these solutions were sonicated under ultrasonic bath (Model - Meltronics, 20 kHz, 250 W) for half an hour. The solutions prepared in normal and sonicated conditions were kept in muffle furnace (Model - Deluxe Zenith) first at 100°C for 2 h and then the temperature of the furnace was raised up to 900°C and calcined for 2 h. The solid composites prepared were then cooled to room temperature and treated as catalyst for phenol degradation. 

A useful and simple method for the one-pot preparation of highly functionalized, enanhomerically pure cyclopentanes from readily accessible carbohydrate precursors has been designed by Chiara and coworkers [73]. The procedure depends on a samarium(II) iodide-promoted reductive dealkoxyhalogenahon of 6-desoxy-6-iodo-hexopyranosides such as 7-160 to produce a 6,e-unsaturated aldehyde which, after reductive cyclization, is trapped by an added electrophile to furnish the final product. In the presence of acetic anhydride, the four products 7-161 to 7-164 were obtained from 7-160. 

Samarium(II) iodide also allows the reductive coupling of sulfur-substituted aromatic lactams such as 7-166 with carbonyl compounds to afford a-hydroxyalkylated lactams 7-167 with a high anti-selectivity [74]. The substituted lactams can easily be prepared from imides 7-165. The reaction is initiated by a reductive desulfuration with samarium(ll) iodide to give a radical, which can be intercepted by the added aldehyde to give the desired products 7-167. Ketones can be used as the carbonyl moiety instead of aldehydes, with good - albeit slightly lower - yields. 

The (C Me ) Sm(THF) metal vapor product provided the first opportunity ta see if Smdl) complexes (y =3.5—3.8 Ufi) could be characterized by H NMR spectroscopy (24). Fortunately, the paramagnetism doesn t cause large shifting and broadening of the resonances and hence samarium provides the only Ln(III)/Ln(II) couple in which both partners are NMR accessible. Once the existence and identity of (C Mej- SmdHF) was known, a solution synthesis was developed from KC Me and Sml THF) (44). This system is the preferred preparative route and also provides another soluble organosamarium(II) complex, [(C Me )Sm(THF)2(u-I)]2, under appropriate conditions. This is another xample of how solution studies subsequently catch up to the research targets often identified first in metal vapor reactions. 

Zard and coworkers have developed a synthesis of substituted dienes by reductive elimination of allylic nitroacetates (equation 33)66. Allylic nitroacetates can be prepared by condensation of nitromethane with the carbonyl compound followed by addition of formaldehyde and acetylation67. Reductive elimination can be carried out by employing either chromous acetate or samarium iodide. 

Samarium enolates 60 can be easily prepared by reduction of ct-bromocarboxylic acid esters with SmT. These enolates mediated well-defined synthesis of star-shaped block co-polymers 61 (Scheme 21 ).32 32l Sml3 also mediated the formation of samarium enolates. Phenacyl thiocyanate 6233 and cr-haloketone 6434 are converted to samarium(lll) enolate intermediates 63 and 65, respectively, which undergo addition to benzaldehyde derivatives affording the corresponding oy i-unsaturatcd ketones as shown in Schemes 22 and 23. 

Preparation. Sml2 can also be prepared by reaction of I2 with samarium powder and THF. A yellow suspension of SmI, is formed, which on further reaction with the metal under reflux is converted into Sml2. ... 

The allenyl carboxylate 35 was obtained in an enantiomerically enriched form by the palladium-catalyzed reduction of the racemic phosphate 34 using a chiral proton source [53]. The two enantiomers of the (allenyl)samarium(III) intermediate are in rapid equilibrium and thus dynamic kinetic resolution was achieved for the asymmetric preparation of (i )-35 (Scheme 3.18). 

Two convenient methods have been developed for the preparation of trifluoro-methyl-substituted alkoxyallenes. Reductive elimination of allylic acetates 30 with samarium diiodide leads to 31 (Scheme 8.11) [38], whereas reaction of Wittig cumu-lene 32 with phenyl trifluoromethyl ketone (33) and thermolysis of the intermediate 34 provides 35 (Scheme 8.12) [39]. 

Reduction of diaryltellurium dichlorides with samarium diiodide (typical procedure). Diaryl tellurium dichloride (1 mmol) was added to the deep blue solution of Sml2 (2.2 mmol) in THF (22 mL) at room temperature under nitrogen with stirring. The deep blue colour of the solution disappeared immediately and became yellow. The resulting solution was stirred at room temperature under nitrogen for 30 min. To the solution was added dilute hydrochloric acid, and the mixture was extracted with ether. The ethereal solution was washed with brine and dried over MgS04. The solvent was evaporated in vacuo, and the residue was purified by preparative TLC on silica gel (petroleum ether-methylene dichloride as eluent). 

Recently, rare-earth metal complexes have attracted considerable attention as initiators for the preparation of PLA via ROP of lactides, and promising results were reported in most cases [94—100]. Group 3 members (e.g. scandium, yttrium) and lanthanides such as lutetium, ytterbium, and samarium have been frequently used to develop catalysts for the ROP of lactide. The principal objectives of applying rare-earth complexes as initiators for the preparation of PLAs were to investigate (1) how the spectator ligands would affect the polymerization dynamics (i.e., reaction kinetics, polymer composition, etc.), and (2) the relative catalytic efficiency of lanthanide(II) and (III) towards ROPs. 

Samarium sesquioxide is used in optical and infrared absorbing glass to absorb infrared radiation. Also, it is used as a neutron absorber in control rods for nuclear power reactors. Tbe oxide catalyzes dehydration of acychc primary alcohols to aldehydes and ketones. Another use involves preparation of other samarium salts. 

Samarium sesquioxide may be prepared by two methods (1) thermal decomposition of samarium carbonate, hydroxide, nitrate, oxalate or sulfate ... 

As an example let us consider the pentacene/samarium interface (Koch et al, 2002). Samarium has a low work function ((/>m — 2.7 eV), which is comparable to E a from pentacene (— 2.7 eV). Thus, if A 0, the condition Ep, should provide efficient electron injection because in this case fp and LUMO are nearly aligned. In order to avoid contamination that may alter the instrinsic m, h and homo values, such heterostructures have to he prepared in ideally clean conditions, imposing the use of UHV. The UPS experiments performed with synchrotron radiation are shown in Fig. 4.24. After measuring (pM of the clean samarium surface (2.7 eV) as described above, increasing amounts of pentacene are controllably deposited onto the samarium surface. The survey spectra of the valence states and a close-up view of the energy region near E are shown in Figs. 4.24(a) and (b). 

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