Organometallic divalent samarium

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]. 

Ihara, E., Nodono, M., Katsura, K. etal. (1998) Synthesis and olefin polymerization catalysis of new divalent samarium complexes with bridging bis(cyclopentadienyl) Ugands. Organometallics, 17, 3945. 

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. 

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)... 

The exploration of Lnl2(THF) c, in particular, Sml2(THF)4, which is prepared by the reaction of samarium metal with ICH2CH2I in THF [96], or the reaction of iodine with an excess of samarium metal in THF, provides appropriate starting materials for divalent organometallic complexes (Equation 8.29). 

The greatest impact of the CsMes ligand on divalent organolanthanide chemistry has been with samarium. In contrast to Eu and Yb, the unsubstituted cyclopentadienyl derivatives of samarium, [(C5H5)2Sm] 84) and [(CH3C5H4)2Sm] 113), are insoluble in common solvents. Hence, prior to the synthesis of the alkane-soluble (CsMe5)2Sm(thf)2 114), there was no opportunity to explore the organometallic chemistry of Sm(II), the most reactive of the divalent lanthanides. 

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-... 

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. 

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). 

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