Yb metal

Figure 5.8. Lanthanide Ln203 oxides (cubic cI80-Mn2O3 type, on the left side) and Pb alloys (LnPb3, cubic cP4-type, on the right). The trends of the lattice parameter and of the heat of formation are shown (see the text and notice the characteristic behaviour of Eu and Yb). A schematic representation of the energy difference between the divalent and trivalent states of an ytterbium compound is shown. Apromff represents the promotion energy from di- to trivalent Yb metal, A,//11, and Ar/Ynl are the formation enthalpies of a compound in the two cases in which there is no valence change on passing from the metal to the compound the same valence state (II or III) is maintained.

Among the various methods available for the activation of dienes in a Diels-Alder reaction, Lewis acid catalysis is certainly the most important. Our group has reported the first example of a Diels-Alder reaction catalyzed by Bi(0Tf)3xH20 (Scheme 12) [72], which showed high catalytic activity and regioselectivity in comparison to other Sc-, Ti-, Sm-, or Yb-metal-based Lewis acids, well-known for their efficient catalytic activity. Bi(OTf)3 proved to be slightly more endo-selective than Sc(OTf)3. Further, no polymerisation of dienes or dienophiles was observed. Bi(OTf)3 was also found to be superior to SnCI4 and Cu(BF4)2. 

Ybi4MnSbn crystallizes with the CaMAlSbn structure type a = 1.6615, c = 2.1948 after Chan et al. (1998) from X-ray single crystal diffraction. A single crystal was obtained by heating a mixture of elements to 1273-1473 K for 5-10 days and cooling the reaction to room temperature at a rate of 60°C/h. The starting materials were dendritic Yb metal 99.999% Sb 99.9999% Mn flakes 99.98%. 

Complexes of the type Cp2Ln, Ln = Yb, Eu are obtained by dissolving the metal Yb or Eu in liquid ammonia in the presence of cyclopentadiene [117]. Another method consists of reduction of Cp2YbCl with Na or Yb metal in THF. These compounds are air sensitive and ionic in character as evidenced by IR and Mossbauer spectral data [57]. 

The first compound with one Cp ligand to be synthesized was the Yb complex. The complex Cp Yb(/r2-I)3Li(Et20)2 was obtained by the reaction [190] of Yb metal with... 

Yb has a 4f13 configuration and the metal gives a doublet structure due to spin-orbit interaction. On the other hand, oxidized Yb metal gives extended multiplet structure indicating the promotion of one of the f electrons to the valence shell. Fig. 9.9 shows the XPS spectrum of Yb metal, Yb metal with oxygen and Yb203. The multiple structure has been attributed to 4f"-4d9 interaction. 

The Auger spectrum of YbAl3 in the 4d-4f-4f region showed no significant difference from that of Yb metal with 4f14 configuration. In this case the valence electron transfer is due to the 4d hole state and the processes involved in valence electron transfer are shown below. 

The above interface studies have demonstrated that the application of a bilayer cathode consisting of an ultrathin CsF and a Yb metal leads to the liberation of low metal atoms that would act as n-type dopants in the polymer... 

Among all low-valent lanthanides, the zero valent Sm and Yb metals are the most often used reducing agents for the study of two-electron reduction of ketones. 

Reaction of Yb metal powder with 1 equivalent of benzophenone in THF/HMPA gives the Yb(II) benzophenone dianion complex [Yb(m-h1,h2-OCPh2)(HM-PA)2]2 (14) as purple crystals (Scheme 12) [21,24]. X-ray analysis has revealed that complex 14 possesses a dimeric structure, in which the two Yb atoms are bridged by two benzophenone dianions. The bridge is built in such a manner... 

Similar to diaryl ketones, aromatic thioketones and imines can also be reduced to the corresponding dianionic species. Fujiwara and coworkers have reported that the ytterbium diaryl thioketone dianion species, generated by reaction of Yb metal with the thioketones in THF/HMPA at low temperature, show good nucle-ophilicity towards organic substrates such as acetone and alkyl halides (Scheme 22) [31]. The thioketone dianion species seemed to be less stable than those of ketones. At room or higher temperatures, C-S bond cleavage reaction took place. 

Reaction of N-(diphenylmethylidene)aniline with 1 equivalent of Yb metal in THF/HMPA gives the corresponding dianionic complex Yb(h2-Ph2CNPh)(HM-PA)3 (26) whose structure has been crystallographically determined (Scheme 23) [32]. The imine dianion complex 26 is more basic and less nucleophilic than ketone- and thioketone-dianion species. It reacts with C02 to give after hydrolysis the corresponding Yb(III) amino acid derivative [33],but with acetone to release... 

Co and Ni are normally active for the hydrogenolysis of alkanes, whereas Eu and Yb metal powders prepared by the metal vapor technique are not active under similar reaction... 

Fig. 17.31 Yb 66-7-keV spectra of (a) Yb metal, (b) YbClj.eHiO polycrystalline, (c) YbCl3.6H20 single crystal with magnetic axis perpendicular to direction of observation. [Ref. 184, Fig. 1]... 

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