Lanthanide samarium complexes

Different lanthanide metals also produce different emission spectrums and different intensities of luminescence at their emission maximums. Therefore, the relative sensitivity of time-resolved fluorescence also is dependent on the particular lanthanide element complexed in the chelate. The most popular metals along with the order of brightness for lanthanide chelate fluorescence are europium(III) > terbium(III) > samarium(III) > dysprosium(III). For instance, Huhtinen et al. (2005) found that lanthanide chelate nanoparticles used in the detection of human prostate antigen produced relative signals for detection using europium, terbium, samarium, and dysprosium of approximately 1.0 0.67 0.16 0.01, respectively. The emission... 

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... 

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 first lanthanide-NHC complexes were isolated by Arduengo and coworkers in 1994.62 A stable carbene displaces THF in bis(pentamethylcy-clopentadienyl)-samarium-THF to form the samarium(II)-NHC complex 55 (Scheme 29). The addition of a second equivalent of NHC resulted in the isolation of the bis(NHC) adduct 56. Compound 56 was characterised in the solid state by single crystal X-ray diffraction and exhibits samarium-NHC bond distances of 2.837(7) A and 2.845(7) A, which are longer than the M-C bond in a-bonded alkyl lanthanide complexes. 

The first tris(pentamethylcyclopentadienyl) lanthanide complex was isolated accidentally from the reaction of a divalent samarium complex (CsMes )2Sm with cyclooctatetraene [9]. Following this discovery, two more convenient methods were developed for the preparation of the sterically crowded complexes (C5Mes)3Ln [10],... 

The non-classical divalent lanthanide complexes have stronger reducing power than divalent samarium complexes because of their higher reduction potentials. Dinitrogen is not an inert atmosphere for these non-classical divalent lanthanide complexes. Therefore, attempts to prepare non-classical divalent organolanthanide complexes by metathesis reactions in dinitrogen atmosphere have been unsuccessful, and the dinitrogen-activated products were isolated. A typical example is shown in Equation 8.36 [112]. 

Because the 5d orbitals of lanthanide metals are shielded by 4f orbitals, the lanthanide metals cannot effectively back-bond like the transition metals, and the alkynes and the CO are expected to have no significant chemistry with organolanthanide complexes. However, the divalent samarium complex (C5Me5)2Sm(THF)2 can reduce diphenyl ethyne, and subsequently activate CO to generate a tetracyclic compound, as shown in Figure 8.33 [113]. 

It is worth noting that the sterically crowded tris(pentamethylcyclopentadienyl) lanthanide complexes (C5Mes)3Ln have similar reductive reactivity to the divalent samarium complex. This phenomenon has been termed sterically induced reduction (Section 8.2.1.2). 

Hou, Z.M., Zhang, Y, Tardif, O. etal. (2001) (Pentamethylcyclopentadienyl)samarium(II) alkyl complex with the neutral CsMesK ligand a precursor to the first dihydrido lanthanide(III) complex and a precatalyst for hydrosilylation of olefins. Journal of the American Chemical Society, 123, 9216. 

Fluorosulfate, tetrabutylammonium, 26 393 Formic acid, rhenium complex, 26 112 Furan. tetrahydro-, iron complex, 26 232 lanthanide-lithium complexes, 27 169 lutetium complex, 27 152, 153, 161, 162 magnesium complex, 26 147 neodymium complex, 27 158 neodymium and samarium complexes, 26 20... 

The dimeric rare-earth metal dichloride complexes [Ln(L30)Cl2]2 (Ln = Y (135), Sm (136), Dy (137), Er (138), Yb (139), Lu (140)) were obtained from the salt metathesis reaction of potassium bis(phosphinimino)methanide KL30 with anhydrous yttrium or lanthanide trichlorides (Scheme 49) [104]. When the metal center is larger than samarium, bis(phosphinimino)methanide lanthanide dichloride complexes could not be obtained. 

Marks has developed a class of remarkably effective catalysts for the enanti-oselective hydrogenation of 2-phenyl-1-butene [29,35,36,37]. Incorporation of a menthyl chiral auxiliary on the 3-position of an a sa-bis(cyclopentadienyl) ligand leads to two diastereomeric complexes of samarium 30 [29]. Similarly, the neomenthyl-substituted complexes 31 can be formed and isolated as pure diastereomers. These complexes are very active catalysts for the hydrogenation of 2-phenyl-l-butene under mild conditions (25 °C, 100-1000 1 substratercata-lyst, 760 mm H2,5 min) [29]. As shown in Table 5, as the lanthanide metal in neomenthyl-substituted complexes 31 becomes smaller, the enantioselectivity decreases from 58% ee (La) to 10% ee (Lu) (entries 1-5). Using a 70 30 mixture of the diastereomers 30a and 30b of the menthyl-substituted samarium complex the good enantioselectivity at 25 °C (64% ee) becomes superb at -80 °C (96% ee) (entries 6-10). This same mixture of 30a/30b catalyzed the deuteration of styrene at 25 °C in 72% ee. 

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