Organometallic divalent ytterbium

Ba (CN 6) 1.49 A, EN = 0.97) leads to chemistry dominated by electrostatic interactions. There are significant similarities between the chemistry of calcium and divalent ytterbium as well as strontium and divalent europium and samarium owing to quite similar size/charge ratios. SeeScandium, Yttrium the Lanthanides Organometallic Chemistry and Scandium, Yttrium the Lanthanides Inorganic Coordination Chemistry)... 

Yao, Y Zhang, Y Zhang, Z. Shen, Q. Yu, K. Synthesis and structural characterization of divalent ytterbium complexes supported by fi-diketiminate ligands and their catalytic activity for the polymerization of methyl methacrylate. Organometallics 2003, 22, 2876-2882. 

The thermal decomposition of trihalides is a good way to prepare divalent ytterbium and samarium halides (especially iodides). For example, Baernighausen (1961) has prepared excellent samples of Sm or Yb dihalide by the thermal decomposition of trihalide hydrates. Only a few preparations involve this type of reaction in the field of divalent organometallic compounds. 

Divalent ytterbium and samarium derivatives are generally highly imstable in the presence of oxygen and must be kept under an inert atmosphere. It is the samarium compounds which are the most reactive. Oxidation end-products should be mixtures of various species such as LnXO, Lu203 and LnXj. Organometallics are often extremely sensitive to air, for example, Yb(C4F5)2(THF)4 (Deacon et al., 1977) and SmCp2 (Watt et al., 1969). 

Until recently the divalent organolanthanides were only briefly studied as Grignard-like reagents. D.F. Evans et al. (1970, 1971) prepared organometallic compounds of divalent ytterbium by the reaction of ytterbium metal on alkyl or aryl iodides in THE at — 20°C. Magnetic susceptibility measurements showed that 75-92% of the ytterbium is present in the divalent state. The solutions react on aldehydes or ketones as typical Grignard reagents. 

W. J. Evans, M. A. Johnston, M. A. Greci, and J. W. Ziller, Synthesis, Structure, and Reactivity of Unsolvated Triple-Decked Bent Metallocenes of Divalent Europium and Ytterbium, Organometallics 18, 1460-1464 (1999). 

Divalent samarium complexes can also catalyze ethylene polymerization, initially through one-electron transfer from the Sm(II) species to an ethylene molecule to form a Sm(III)-carbon bond, which is the active intermediate that induces ethylene polymerization. The less reducing divalent organometallic ytterbium and europium complexes are generally inert [143]. 

The most fundamental precursors to organometallic complexes of group 3 elements are the trichlorides, MCI3. The commercially available trichlorides are hydrated, and even for those claimed dehydrated it is advisable to take the appropriate steps necessary to dry them further before use. The divalent iodide complexes Ml2 are available for certain group 3 elements such as samarium and ytterbium, and they serve as conve-... 

In the specific case of scandium, mono- and mixed-valence species can also be isolated together with divalent complexes for instance, a Sc organometallic compoimd could be obtained imder relatively mild conditions. Finally, the author describes the few knovm zerovalent bis(arene) rare-earth complexes which have been obtained by co-condensation of arenes or heteroarenes with metal vapors. In his conclusion, F. Nief notes that the low-valence molecular chemistry of rare earths, which was once thought to be restricted to divalent samarium, europium, and ytterbium, has been extended to several other rare earths, as well as to lower valence oxidation states. It is the opinion of the author that this research area is likely to find fascinating developments in a near future. 

Similar divalent metallocene complexes of ytterbium, i.e., (Cp),Yb(base/ligand) y, were also shown to act as mild, one-electron reducing agoits toward transition metal carbonyl compounds such as Co2(CO)g (Tilley and Andarsen, 1981), CpCo(CO)2 (Boncella and Andersen, 1984) and other organometallic derivatives of cobalt. 

A metal vapor technique provides a very interesting route to the preparation of Sm(II) or Yb(II) organometallic species. Thus W.J. Evans et al. (1980, 1981a, 1982) were able to prepare several substituted dicyclopentadienyl samarium and ytterbium complexes. Sm(C5Mes)2 was the first known soluble divalent organosamarium complex. 

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