Lanthanide organometallics reactivity

Compounds of these metals involving either a- or tt-bonds to carbon are generally much more reactive to both air and water than those of the d-block metals. Thus there is no lanthanide equivalent of ferrocene, an unreactive air- and heat-stable compound. They are often thermally stable to 100 °C or more, but are usually decomposed immediately by air (and are not infrequently pyrophoric). Within these limitations, lanthanide organometallic compounds have their own special features, often linked with the large size of these metals. 

Surface organometallic chemistry with rare-earth metals (or lanthanides) on various inorganic oxides has advanced considerably during the past decade but is still in its infancy. A major drawback has been the difficult access and handling of pure (homoleptic) Ln alkyl precursors with reactive Ln-C(alkyl) bonds [101]... 

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. 

A major effort to study the chemistry of the zero oxidation state lanthanides on a preparative scale involved their reactivity with neutral unsaturated hydrocarbons 14, 60). This class of reagents was of interest because reactions of unsaturated hydrocarbons with metals constitute such an important component of organometallic chemistry and because species such as alkenes and alkynes were not common as ligands or reactants in organolanthanide chemistry at that time. 

The thesis that the lanthanide elements offer something unique to organometallic chemistry has been proven in a variety of ways. New classes of complexes, unusual structural tj es, and novel reactivity patterns have been observed with these elements. In addition, the special properties of the lanthanide elements have allowed major contributions to be made to our knowledge of a variety of fundamental organometallic reactions of general interest including the polymerization of alkenes, the activation of C—H and H—H bonds, and the reduction of CO. 

Sanchez-Barba, L.F., Hughes, D.L., Humphrey, S.M. et al. (2005) New bis(allyl)(diketiminato) and tris(allyl) lanthanide complexes and their reactivity in the polymerization of polar monomers. Organometallics, 24,3792. 

Voskoboynikov, A.Z., Parshina, I.N., Shestakova, A.K. et al. (1997) Reactivity of lanthanide and yttrium hydrides and hydrocarbyls toward organosilicon hydrides and related compounds. Organometallics, 16, 4041. 

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. 

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