Sm complexes

Figure 1.26. Asymmetric Meerwein-Ponndorf-Verley-type reduction of ketones catalyzed by a Sm complex.

Following their earlier work13 on the synthesis of oxalohydroxamates of rare earths, Brahma and Chakraburtty73 have also reported the synthesis of some lanthanon/salicylhydroxamate complexes of the composition Ln(0-Cs H4CONHOH)3 - 2H20 (where Ln = La, Ce, Nd, Sm or Eu). La, Ce and Sm complexes tend to lose both molecules of water in the temperature range 90-160 °C with endothermic peaks at 120, 110 and 115°C, respectively. 

Incorporate structural information of protein-SM complexes intD VS paradigm... 

The anionic copper complexes of N1,N4-Ai5(salicylidene)isosemicarbazidate ion (L) are used in the reactions above. As a result of their interaction with lanthanum and samarium chlorides in chloroform-methanol suspension, the heteronuclear Lu,La-or Cu,Sm-complexes are formed [449]. 

Using bulky ligands or chelating ligands to saturate the complexes coor-dinatively or sterically, the rare-earth complexes without n ligands have been obtained and characterized. The La and Sm complexes with bulky alkyl ligands... 

Recent studies have illustrated a number of interesting synthetic pathways to metal-tin bonds. For example the metal exchange reaction involving Yb and Sm complexes leads to new rhenium-tin compounds (equation 121)285. 

M 1min 1), and Km = 225 (M 1). These results indicate a fairly large association constant (Km) for the Sm complex and a rate acceleration of sixteenfold (kBm/kB) by Mg2+ ion. These values may become larger as the water content of solvent becomes lower. 

The reactions of Cp(Sm(THF)2 with a variety of alkenes in hexane or toluene solvent to produce allyl and alkene products have been studied. Binuclear Sm complexes have been synthesized [159] by the reaction of Cp Sm with pyrene, anthracene, 2,3-benzanthracene, 9-methylanthracene. The structure of the complex [(Cp Sm)2(/r-/73 /73-CioHi4)] is shown in Fig. 6.16. 

The NMR spectrum of the La complex is similar to ionic NaC9H7 but the spectrum of the Sm complex showed a decrease in ionic character. The structure of Sm(Ind)3 consists of symmetrical coordination by indenyl rings with an average Sm-C distance of 2.75 A and the angle between Sm atoms and the normal to the planes of the indenyl rings is nearly 120°. There is no preference in bonding to the electron-rich C-l position thus indicating the bonds to be primarily ionic in nature [225]. 

The X-ray structure of the Sm complex [247] shows one of the Cp Sm units rotated with respect to the second one by 87° such that the molecule shows approximate S4 symmetry. 

The Sm complex [254] is characterized by a formal twenty electron configuration. The Sm atom is coordinated by four hydrides. The heterometallic complex of Y and Re has an open triangular structure as shown in Fig. 6.26. The Re(2)-Y distance is 4.186 A and the other Re(l)-Y distance of 3.090 A. This suggests the presence of a hydride bridge for Re(l)-Y. Short Re-Re distance of 2.576 is also accounted for by the earlier explanation. The bridging hydride structure is also supported by NMR data [255]. 

X-ray analysis of the Yb complex [249] shows the two coordination tetrahedra around Yb and Ce are linked by a CO bridge. A large number of lanthanide complexes with Ln-OC-M bridges have been characterized [259]. Tetrathiometallate anions have been used for the synthesis of mixed metal [261], Mo-Sm, W-Sm complexes such as [Cp Sm]2Mo(/r-S)4]PPh4. 

The Sm + ion with 4f -orbital configuration has numerous energy levels, even covering the NIR spectral range (Figure 11.27), which may be the reason that the PL quantum yields of most Sm complexes are very low. 

The papers cited above include studies of La and Lu " EDTA-type complexes, (308, 309, 311, 312) Cu complexes, (314, 315) Fe " complexes, (310) and Sm " complexes. (316, 317) Kinetic parameters and stability constants have been calculated in many cases. In one study (315) the variation in the relaxation time of [Cu(EDTA)(H20)] was followed on gradual addition of ammonia at pH 9. Values were found to shorten and then remain constant after addition of a ten-fold excess of ammonia. This is due to the formation of [Cu(EDTA)(NH3)2] " with a formation constant of 18-8. 

For example, random copolymerization of 1-hexene with ethylene was initiated by complex 5(Lu H) [37]. The ratio of ethylene/1-hexene in the polymer of 3 1 indicates the sensitivity of chain propagation toward steric bulk of the incoming monomer. Precatalyst 4(Lu H) effects the random copolymerization of ethylene with methylenecyclopropane to achieve 65 exo-methylenes per 1000 CH2 units [87]. CsMej/ER-ligated Sm complexes 18 can not only homopolymerize styrene... 

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