Organometallic divalent lanthanides

The first definitive descriptions of organometallic divalent lanthanide complexes (Evans et al., 1970,1971) also alluded to applications similar to Grignard methodology [eq. (69)]. 

Acidolysis of organometallic divalent lanthanides is classical (D.F. Evans, 1970, 1971). It regenerates the organic moiety as it oxidizes the divalent metal ... 

Organometallic compounds of lanthanide metals other than Sm, Eu, and Yb are very rare until now. But the development of this chemistry became possible after the synthesis of divalent precursors of Tm, Dy, and Nd in the late 1990s, namely of their diiodides (see Scandium, Yttrium the Lanthanides Inorganic Coordination Chemistry) and by using hgands such as phospholyl or arsolyl, which stabilize divalent lanthanide ions. 

Giesbrecht, G.R., Cui, C.M., Shafir, A. etal. (2002) Divalent lanthanide metal complexes of atriazacyclonoane-functionalized tetramethylcyclopentadienyl ligand X-ray crystal structures of [C5Me4SiMe2( Pr2-tacn)]Lnl (Ln=Sm, Yb tacn=l,4-diisopropyl-l,4,7-triazacyclononane). Organometallics, 21, 3841. 

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. 

Reduction of dinitrogen molecule by divalent lanthanide complexes has been a popular subject in coordination and organometallic chemistry of the lanthanide elements. In the course of these studies, a large number of polynuclear lanthanide clusters featuring a core of lanthanide atoms organized around a dinitrogen unit have been obtained and structurally characterized. 

Divalent lanthanide compounds are generally non-volatile this observation is consistent with a polymeric constitution. However, some organometallic compounds have been sublimed. Yb(Me3SiC5H4)2 sublimes at 300°C/10 Torr (Lappert et al., 1980) and YbCp2 sublimes at 360°C/10 Torr with considerable decomposition (Calderazzo et al., 1966). 

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)... 

There are two low-valent oxidation states available to the lanthanides under normal conditions the +2 oxidation state and the formally zero oxidation state found in the elemental metals. The zero oxidation state is available to all the lanthanides, but only three members of the series have +2 oxidation states accessible under common organometallic reaction conditions Eu (4/ ), Yb (4/ ), and Sm (4/ ). The Ln VLn" reduction potentials [vs. normal hydrogen electrode (NHE)] (12), - 0.34 V for Eu, - 1.04 V for Yb and - 1.50 V for Sm, indicate that Eu is the most stable and Sm the most reactive of these divalent ions. Sm is also the most reactive based on radial size considerations, since it is the largest and most difficult to stabilize by steric saturation. 

Homogeneous Catalysis Lanthanide Halides Organometallic Chemistry Fundamental Properties Tetravalent Chemisiry Inoiganic Tetravalent Chemistry Organometallic The Divalent State in Solid Rare Earth Metal Halides The Electronic Structure of the Lanthanides. 

This review covers all organometallic complexes of Sc, Y and the lanthanides reported in the year 2000 and their reactions. Endohedral fullerene complexes of the lanthanides have, as usual, been excluded. Highlights this year include striking reports of lanthanides in non-classical oxidation states (Sections 3.2 and 5), a remarkable reversible dinitrogen activation described in Section 3.9.2 and evidence for the existence of the divalent hydrides LnH2(THF)2 (Ln = Sm, Yb) (Section 3.10). In addition Evans has assessed the utility of electrospray mass spectrometry for the characterization of organolathanides. The results are promising and the spectra and dissociation patterns show sensitivity to the metal and its oxidation state. ... 

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