Ytterbium oxidation-reduction

The principal sources of ytterbium are euxenite, gadolinite, monazite, and xenotime. the latter being the most important. Ytterbium is separated from a mixture of yttrium and the heavy Lanthanides by using the sodium amalgam reduction technique. Ytterbium metal is obtained by heating a mixture of lanthanum metal and ytterbium oxide under high vacuum. The ytterbium sublimes and is collected on condenser plates whereas the lanthanum is oxidized to the sesquioxide. 

Oxidative-reductive transmetalation of ytterbium metal with diorganomercury compounds has been utilized as an entry to dialkynyl- and polyfiuorinated diaryl-ytterbiums (equations 85 and 86). The dial-kynylytterbiums are indefinitely stable in an inert atmosi iere at room temperature. On the other hand, the polyfiuorinated diarylytterbiums exhibit variable stability. Isolated yields are often low owing to thermal dec< nposition of these organ< netallics. However, most can be generated in nearly quantitative yields by this procedure and simply characterized in situ. 

Kashiwazaki67 has fabricated a complementary ECD using plasma-polymerized ytterbium bis(phthalocyanine) (pp—Yb(Pc)2) and PB films on ITO with an aqueous solution of 4M KC1 as electrolyte. Blue-to-green electrochromicity was achieved in a two-electrode cell by complementing the green-to-blue color transition (on reduction) of the pp—Yb(Pc)2 film with the blue (PB)-to-colorless (PW) transition (oxidation) of the PB. A three-color display (blue, green, and red) was fabricated in a three-electrode cell in which a third electrode (ITO) was electrically connected to the PB electrode. A reduction reaction at the third electrode, as an additional counter electrode, provides adequate oxidation of the pp Yb(Pc)2 electrode, resulting in the red coloration of the pp—Yb(Pc)2 film. 

Solutions of alkali metals in ammonia have been the best studied, but other metals and other solvents give similar results. The alkaline earth metals except- beryllium form similar solutions readily, but upon evaporation a solid ammoniste. M(NHJ)jr, is formed. Lanthanide elements with stable +2 oxidation states (europium, ytterbium) also form solutions. Cathodic reduction of solutions of aluminum iodide, beryllium chloride, and teUraalkybmmonium halides yields blue solutions, presumably containing AP+, 3e Be2, 2e and R4N, e respectively. Other solvents such as various amines, ethers, and hexameihytphosphoramide have been investigated and show some propensity to form this type of solution. Although none does so as readily as ammonia, stabilization of the cation by complexation results in typical blue solutions... 

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). 

Divalent lanthanide chemistry has been dominated by the most readily accessible divalent lanthanide metals samarium(II), europium(II), and ytterbium(II) (classical ) for decades, and a large number of divalent lanthanide compounds have been prepared [92], There are three routes to generate divalent organolanthanide complexes oxidative reaction of lanthanide metal, metathesis reaction of a divalent lanthanide halide, and reductive reaction of a trivalent lanthanide complex. 

The decomposition of europium oxalate [82] occurred at a significantly lower temperature (520 K). Results were interpreted as indicating cation reduction to the divalent state. In vacuum, the products of decomposition were europium(II) carbonate and finely-divided carbon. In carbon dioxide at 593 K, europium(II) oxalate is stabilized. In an oxidizing atmosphere, europium is reoxidised and EU2O3 is formed at 663 K. A reaction mechanism was proposed in which carbon monoxide reacted with the oxalate ion to form carbon dioxide and 203. The reactions of ytterbium oxalate were similar. 

The formation temperatures and the thermal stabilities of the rare earth sulphates, oxides, and oxide sulphates have been investigated. The thermal decomposition of the chromates of several tervalent lanthanides (praseodymium, gadolinium, terbium, dysprosium, holminum, erbium, and ytterbium) has been found to occur with loss of oxygen and reduction of Cr to Cr by a mechanism involving electron transfer from the co-ordinated oxygen to chromium. ... 

A bimolecular route is also postulated to explain the reduction of less electron rich hydrides when the lower oxidation state is accessible (samarium and ytterbium). Thus, the hydrogenolysis of analogous neodymium and samarium hydrides bearing tetramethylphospholyl ligands leads to the stable neodymium hydride and to the reduced samarium(II) metallocene, respectively (Scheme 8). 

The hydrated ions of europium, ytterbium or samarium can be obtained by electrolytic reduction or by dissolution of MCI2 in water, and are reasonably stable. Colourless or pale yellow-green Eu (aq) is stable for more than ten days in the absence of oxidizing agents or of platinum catalysts. Pale ween Yb (aq) decays in water with /c = 2.4 x 10 s, and red Sm (aq) has = 0.6 X both reactions being first order. These rates of decom-... 

A large error in this procedure may occur in the ignition of oxalates to oxides. Aside from mechanical losses on ignition, there is some evidence that furnace atmosphere conditions are of importance. If crucible linings are etched during the ignition, erratic results will be obtained. Since this may be due to partial reduction of samarium, europium, or ytterbium, an... 

The major breakthrough occurred in 1953 when the Ames Laboratory team (Daane et al. 1953) reported the preparation of samarium, europium and ytterbium in high purity and high yields by the reduction of their oxides with lanthanum metal in a vacuum. With the preparation of samarium metal, finally, 126 years after the first rare earth element was reduced to its metallic state, all of the naturally occurring rare earths were now available in their elemental state in sufficient quantity and purity to measure their physical and chemical properties. The success of this reaction is due to the low vapor pressure of lanthanum and the extremely high vapor pressures of samarium, europium and ytterbium (Daane 1951, 1961, Habermann and Daane 1961). It is interesting to note that this same technique has been the method of choice for the preparation of some transplutonium metals (Cunningham 1964). 

---