Samarium electron system

Other electron-donating systems include zinc dust and Me3SiCl, that gives the silyl ethers8 such as 40, or samarium iodide that gives similar dimers of aromatic aldehydes in excellent yield.9 These reactions usually favour the anti -isomers 40 and 42. 

To avoid secondary reductive steps, low concentrations of the active low-valent metal are advantageous, i.e. the use of catalytic one-electron reduction cycles [31]. Low-valent vanadium species are efficient catalysts for pinacolization. After the primary electron transfer, the oxidized vanadium catalyst can be reduced by Zn(0) or by aluminum [32], TrialkyIsilanes have to be added to decomplex the oxidized vanadium catalyst from the pinacol [33]. The same catalytic system can also be used for the synthesis of 1,2-diamines via coupling of aldimines [34]. Alternatively, a titanium (Il)-samarium system gives the 1,2-diamines with moderate D,L-selectivity [35]. 

In contrast, Matsukawa and Hinakubo proposed Sm(II)-mediated pinacol coupling in water (Scheme 8.11).11 In all cases, the corresponding reduced product benzyl alcohols were formed in low yields. Unexpected disproportionation in water was also observed via UV-visible spectroscopic analysis. This indicated that low-valent samarium species can exist in water. Furthermore, the SmCl3-Sm and SmCl3-Mg systems were found to act as good one-electron reducing agents in water (Scheme 8.11). 

It is noteworthy that while the electron rich Cp 2SmH is only moderately stable in solution, the analogous more strained dinuclear bridging complex is less stable and must be kept under hydrogen in order to record the NMR spectrum [2]. The synthesis of a samarium hydride supported by a calix-tetrapyrrolyl system was recently published [9] (Scheme 2), with the hydride ligand bonded to one samarium and to two lithium atoms. This cage affords an efficient protection against bimolecular collisions and the complex is described as thermally robust. 

Meanwhile N. Bohr was working on the theory of electron shells in atoms which also became the corner-stone of the periodic system theory and, at last, explained the periodic changes in the properties of chemical elements. Bohr also solved the problem which had interested chemists for many years he found the exact number of rare-earth elements. There had to be fifteen of them from lanthanum to lutetium. Only one REE between neodymium and samarium (later known as promethium, see p. 208) remained unknown. Bohr came to this conclusion on the basis of the laws found by him which governed the formation of electron shells of atoms with increasing Z. 

No isothermal section is available for the ternary Sm-Zn-Ge system, however one ternary compovmd was observed and characterized by Rossi and Ferro (1996). SmZni.5Geo.5 was found to crystallize with the AIB2 type, a = 0.4412, c=0.3737 from X-ray powder diffraction of an induction melted alloy which was annealed at 1070K for one week. An electronic micrographic examination, as well as microprobe microanalysis, was carried out. The metals employed in the s5mthesis of samples had a nominal purity of 99.9mass% for samarium, and 99.999 mass% for other metals. 

A high-speed impact test system with an electron thermal (ET) gun is illustrated in Fig. 1. First, a substrate with coating film is mounted on a specimen holder. The specimen is to be mounted mechanically in line with the ET gun and the solenoid coils. Then, a spherical magnet of samarium-cobalt (Sm2Con, density 8.4g/cm, hardness 5.4 GPa, Young s modulus 151 GPa, strength 118 MPa) is mounted in a plastic sabot as a simulated foreign object. 

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