Ytterbium metal

Figure 4.17. The binary phase diagrams of the magnesium alloy systems with the divalent metals ytterbium and calcium (Ca is a typical alkaline earth metal and Yb one of the divalent lanthanides). Notice, for this pair of metals, the close similarity of their alloy systems with Mg. The compounds YbMg2 and CaMg2 are isostructural, hexagonal hP12-MgZn2 type.

After separation from other rare earths, ytterbium is usually obtained as its oxide, Yb203. If separated as oxalate, oxalate is converted into oxide by high temperature. Ytterbium oxide is reduced to metallic ytterbium by heating with lanthanum metal in high vacuum. The metal is purified by sublimation and collected over a condenser plate. Aluminum, zirconium, and cerium also are effective reducing agents and may be used instead of lanthanum. 

Active catalyst species or catalysis intermediates can often be trapped by stoichiometric reactions of the precatalyst with the substrate. The following example describes the successful isolation of such an intermediate with participation of Ln-O cr-bonds. Reduction processes mediated by low oxidation states of the lanthanide elements are of special interest in organic synthesis [256]. One of the most intensively studied reactions is the stoichiometric reduction of arylketones by rare earth metals ytterbium and samarium [277]. Thus formed dianions possess high nucleophilic character and excess lanthanide metal can even accomplish complete cleavage of the C-O double bond (Scheme 36). 

The reaction of a lanthanide metal, ytterbium, has been explored by the group of Fujiwara [164-166]. Among the various processes (coupling, desul-furisation, etc.) which were evidenced, a nice application was achieved by successive reaction of thiobenzophenone with ytterbium, and treatment of the intermediate with a dihalide. Thiolanes, for instance, were thus obtained in an expedient manner. 

Highly electropositive elements such as metallic ytterbium undergo oxidative addition reactions even with imines to give azametallacyclopropanes15 ... 

The rednctive conpling (see Reductive Coupling) of acenaphthylene by activated metallic ytterbium and samarium yields unra-lanthanidocenes [( ) -Ci2H8)2Ln(THF)2] (Ln = Yb, Sm) (equation 25). 

The reduction of disubstituted acetylenes with ytterbium in liquid ammonia also produces trans-a -kenes in good yields. This reducing system does reduce some double bonds, such as the strained double bond in norbomadiene however, in general, carbon-carbon double bonds do not undergo reduction with this reducing system. The expense of powdered metallic ytterbium does not make this a very practical reducing agent for synthetic purposes. 

In the presence of methyl iodide, metallic ytterbium can easily react with allylbromide in anhydrous THF to form allylytterbium bromide, which reacts readily with imines to give the corresponding bromoallylamines in satisfactory yields under mild and neutral conditions (Scheme 303).1091... 

The first neutral lanthanide(II) silyl complex (Ph3Si)2Yb(THF)4 was synthesized by the reaction of PhsSiCl with metallic ytterbium in THF. The solid complex has a cen-tros3munetrical octahedral structure with a Yb atom bonded to four oxygen atoms of the THF molecules in the equatorial positions and to two Si atoms of the SiPhs fragment in the axial positions. The Yb—Si distance of 3.158(2) A is 0.1 A larger than the Sm—Si distance in Cp2 SmSiH(SiMe3)2 which is in agreement with the difference in ionic radius between Ln(II) and Ln(III) complexes. ... 

Metallic ytterbium is also utilized as a reducer for Cp2YbCl [17]. The yield of dicyclopentadienides in these reactions is 30-40%. The reactions of anhydrous halides LnX2 with sodium and potassium cyclopentadienides may be applied [3, 14, 23, 27, 52] to synthesize REM dicyclopentadienides. 

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