Samarium complex

Samarium, tris(triphenylphosphine oxide)bis-(diethyldithiophosphato)-structure, 1,78 Samarium complexes dipositive oxidation state hydrated ions, 3, 1109 Samarium(III) complexes salicylic acid crystal structure, 2, 481 Sampsonite, 3, 265... 

The fourth chapter gives a comprehensive review about catalyzed hydroamina-tions of carbon carbon multiple bond systems from the beginning of this century to the state-of-the-art today. As was mentioned above, the direct - and whenever possible stereoselective - addition of amines to unsaturated hydrocarbons is one of the shortest routes to produce (chiral) amines. Provided that a catalyst of sufficient activity and stabihty can be found, this heterofunctionalization reaction could compete with classical substitution chemistry and is of high industrial interest. As the authors J. J. Bmnet and D. Neibecker show in their contribution, almost any transition metal salt has been subjected to this reaction and numerous reaction conditions were tested. However, although considerable progress has been made and enantios-electivites of 95% could be reached, all catalytic systems known to date suffer from low activity (TOP < 500 h ) or/and low stability. The most effective systems are represented by some iridium phosphine or cyclopentadienyl samarium complexes. 

Table 11. Ethylene polymerization by divalent samarium complexes...

In addtion to Sm metal, Cp 2Sm(TFlF)B (n = 2 or 0) can be a good starting material for allylsamarium generation. In the case of Cp 2Sm(THF) (n = 2 or 0), allylic ethers are useful precursors since they are able to coordinate to the low-valent lanthanide metal via the internal oxygen. Samarium complexes 45 react with allyl benzyl ether 46 to produce allylsamarium complex 47 and benzyloxide 48 as illustrated in Equation (9).26... 

Catalyzed by a samarium complex, the cycloisomerization of l-(3 -butenyl)-4,5-allenylamine 289 would lead to bicyclic product 292 by a two-fold cyclization reaction [143]. 

C4H602, 2-Propenoic acid, methyl ester platinum complex, 26 138 C4H7NO, 3-Butenamide nickel complex, 26 206 C4HsO, Furan, tetrahydro-iron complex, 26 232 magnesium complex, 26 147 neodymium and samarium complexes, 26 20... 

Evans reported an enantioselective Meerwein-Ponndorf-Verley reduction using a catalytic amount of chiral samarium complex 26 prepared from samarium (III) iodide and a chiral amino diol (Scheme 9.16) [34], Even when a partially resolved ligand (80% ee) was used, the enantiopurity of the resulting alcohol 27 reached 95% ee, which is the same value as that obtained when the enantiopure amino diol was used. 

Corresponding 5-coordinate samarium complexes can also be accomplished (Table 5) [74,75] and heteroatom stabilization of the strongly reducing Sm(II) was observed in the ate complex [KSm(OC6H3tBu2-2,6-Me-4)3(THF)]n [75]. Indefinite chains or higher aggregations by K arene interactions seems to be a common coordination mode in lanthanide aryloxide complexes. 

The divalent samarium complexes (CsMe5)2Sm and (C5Me5)2Sm(THF)2 have also been found to be effective precatalysts in these hydroamina-tion/cyclization reactions [68]. In this case the initial step is the formation of samarium(III) intermediates via allylic C-H activation [Eq. (15)]. 

An intriguing chiral samarium complex for the Meerwein-Pondorf-Verley (MPV) reduction of ketones has been reported by Evans.100 The soluble catalyst, prepared as indicated in Figure 46, promoted the asymmetric MPV reduction of aryl methyl ketones in up to 97% ee with as little as 5 mol % loading (Figure 47). 

Intercalation compounds involving layered double-hydroxides (LDHs), illustrated by the structure shown in Figure 19 (Park et al., 2002), were synthesized to facilitate the measurement of the uniaxial stress (i.e., along the direction perpendicular to the layers), that host layers exert on intercalated species. Below a certain thickness of -A 00 mm, the intercalated structures become more transparent to visible light, so that the information obtained by PL represents the properties of the bulk, not of the surface. Because it is sensitive to the deformation of the intercalants, the PL from samarium complexes was employed to measure the uniaxial stress, by using PL peak positions as a function of pressure (Park et al., 2002 Sapelkin et al., 2000). 

Figures 20A and B show the PL spectra, recorded at 290 K, at 600 nm, and as a function of pressure, for Cs9(SmW10O36) and SmWi0O36-LDH, respectively (Park et al., 2002). For the sake of comparison, the line shapes are normalized and displaced along the vertical axis. In both cases, the peak position is red-shifted by 4—5 nm when the hydrostatic pressure increases from 1 bar to 61 kbar. It was shown that the red-shift from A to A lies solely in the deformation of the samarium complexes by the uniaxial stress exerted by the host layers, whereas the shift from B to B is also influenced by the change in the cation environment. Under the same conditions, B is not at the same position for the non-intercalated (HN (n -b u t y 1) 3) 9 (SmW10O3e) and Cs9(SmWi0O36) compounds (Park et al., 2002). Thus only peak A is available to measure the unixial stress. This observation can be used to determine the uniaxial stress, when the external pressure is zero. For the SmW10O36—LDH system, the uniaxial stress varies significantly from 75 at 28 K to 140 kbar at 290 K (Park et al., 2002).

Because it is sensitive to the deformation of the intercalants, the PL from samarium complexes, such as SmWi0C>369, was employed to measure the uniaxial stress exerted by the host such as LDHs on the intercalants. PL peak positions as a function of the hydrostatic pressure within the range of 1-75 kbar were measured (Park et al., 2002 Sapelkin et al., 2000). 

The crystal radii of the rare earth metal ions decrease in a regular manner along the series. There is vast data suggestive of the formation of predominantly ionic complexes in the case of rare earth ions. Based on electrostatic theory, a direct relationship between the stability constant values and the atomic number of the rare earth metal ion is predicted [12]. In most of the complexes, this correlation of log K with Z holds good for La to Eu although in some cases the europium complexes are less stable than the samarium complexes. Further, this simple relationship is not valid when the heavy rare earth ions Tb to Lu are considered. 

A more sterically hindered system is exemplified by the tris-pentamethyl-cyclopenta-dienyl samarium complex obtained in the reaction [52]... 

The complex Cp2Sm(THF)2 causes multiple bond cleavage to produce multiple bonded species [182], The complex reacts with CO, RC=CR, RN=NR and R2C=CR2 bearing compounds resulting in some useful transformations. The samarium complex Cp SmfTHF reacts with azine containing C=N bond and reduces the azines by one electron per substrate. The reaction is illustrated below. With benzaldehydeazine the... 

The tetrameric samarium complex [204] has four Sm atoms in a tetrahedral disposition with bridging (NHNH)2- anions on each side of the tetrahedron with Sm-Sm distances of 3.563 and 3.552 A. The two NH3 units are coordinated to two Sm centers at a distance of 2.664 A. 

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