Organolanthanide Reagents

An organocerium reagent gave better yields than either the lithium or Grignard reagents in addition to carbonyl at the 17-position on steroids.156 

Additions of both Grignard and organolithium reagents can be catalyzed by 5-10 mol % of CeCl3. 

Organocerium reagents also show excellent reactivity toward nitriles and imines.157 158 Organocerium compounds were also found to be the preferred organometallic reagent for addition to hydrazones in an enantioselective synthesis of amines159  

Cerium reagents have also been found to give improved yields in the reaction of organolithium reagents with carboxylate salts to give ketones. 

Organozinc Reagents In Organic Synthesis, CRC Press, Boca Raton, Florida, 1996. 

The lanthanides are congeners of the Group IIIA metals scandium and yttrium, with the +3 oxidation state usually being the most stable. These ions are strong oxyphilic Lewis acids and catalyze carbonyl addition reactions by a number of nucleophiles. Recent years have seen the development of synthetic procedures involving lanthanide metals, especially cerium.195 In the synthetic context, organocerium 

For example, in addition of trimethylsilylmethyllithium to relatively acidic ketones such as 2-indanone, the yield was greatly increased by use of the organocerium intermediate.199 

Organocerium reagents have been found to improve yields in additions to bicyclo[3.3.1]nonan-3-ones.200 

Imamoto, T. Kusumoto, Y. Tawarayama, Y. Sugiura, T. Mita, Y. Hatanaka, and M. Yokoyama, 

Amides, especially of piperidine and morpholine, give good yields of ketones on reaction with organocerium reagents.203 It has been suggested that the morpholine oxygen may interact with the oxyphilic cerium to stabilize the addition intermediate. 

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Similar reactions of organolanthanide reagents, RLnl (Ln = Yb, Eu, Sm), with hex-aalkyl(aryl) distannanes resulted in formation of reactive organometallic derivatives with... 

Other organolanthanide reagents are covered in Chapter 1.10 in this volume, while selective carbonyl addition reactions pr< noted by samarium and ytterbium reagents are surveyed in Chapter 1.9. 

Alkylation. Organolanthanide reagents derived from lanthanide chlorides, alkyllithiums, and BINOL add to aldehydes with good stereoselectivity. 

Although the structures of these species were not determined, this metal vapor chemistry clearly showed that unsaturated hydrocarbons were viable reagents for lanthanides. Furthermore, this high energy technique showed that new regimes of organolanthanide complexes were accessible under the appropriate conditions. In addition, attempts to understand the synthesis of the products in reac-... 

Tris(i/5-cyclopentadienyl)lanthanides were the first authentic organolanth-anides to be prepared1 and bis(t/5-cyclopentadienyl)lanthanide(II) compounds have played a germinal part in the development of lower oxidation state organolanthanide chemistry.2 These cyclopentadienyls are sources of coordination compounds of structural interest and are reagents for the synthesis of other organolanthanides, for example, bis- and mono(t)5-cyclopentadienyl)lanthanide(III) derivatives.2... 

The most important applications of organolanthanides are as Ziegler-Nutta catalysts in polymerization of olefins and as reagents in stoichiometric organic synthesis. Organolan-thanide compounds are also useful as volatile precursors for MOCVD applications in the... 

Some of the earliest studies of organolanthanide chemistry described reactions of the elemental metals with alkyl and aryl iodide reagents (RI) (67). Analysis of the soluble products obtained for Ln = Eu, Yb, Sm indicated a formula of primarily RLnl although it was acknowledged that this could represent a number of different species in equilibrium. The amount of contamination of the divalent product with trivalent species was observed to follow the order of stability of the divalent states the Eu system was the cleanest, while the Sm system had only 50% of the metal in the divalent state. These species reacted like Grignard reagents. The... 

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. 

Recent advances in organolanthanide synthesis, structural characterization, and reactivity clearly have demonstrated that an extensive, distinctive chemistry is available to the lanthanide elements. The view that the lanthanides have only a limited, ionic chemistry is no longer valid. Not only has a much wider range of ligands and reagents been established as viable in organolanthanide systems, but the recent results also indicate that no class of molecules, not even saturated hydrocarbons like CH4, should be excluded from consideration. 

Divalent organolanthanide complexes can also initiate MMA polymerization. A divalent lanthanide complex, as a single-electron transfer reagent, can readily react with the monomer to generate a radical anion species, which subsequently couples into a bimetallic trivalent lanthanide enolate intermediate, which is the active center. Therefore, divalent organolanthanide complexes serve as bisinitiators for MMA polymerization [160]. 

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