Introduction: Frontiers in Lanthanide Chemistry

Lanthanides are elements of rapidly growing im-portance. They are part of the family of rare earths,which also includes scandium, yttrium, and lantha-num. This thematic issue is mainly concerned withlanthanides, hence the brief and focused title. Theavailability of lanthanides at quite cheap pricesfacilitates their use in chemistry and applications.Much progress has recently been achieved in thecoordination chemistry of lanthanides, in the use oflanthanide-based reagents or catalysts, and in thepreparation and study of new materials. The the-matic issue is a timely enterprise, which covers alarge body of new advances presented by experts andspecialists of these various fields. The 22 articles maybe broadly classified into three groups: coordinationchemistry of lanthanides (synthesis and structure ofcomplexes), organic transformations mediated orcatalyzed by rare-earth compounds, and finally thepreparation and properties of new materials or sen-sors.

The first category (coordination chemistry) includesseven contributions. Aspinall describes the coordina-tion chemistry of chiral lanthanide complexes as wellas their application in catalysis. Edelmann, Freck-mann, and Schumann present the synthesis andstructures of non-cyclopentadienyl organolanthanides,describing the many classes of complexes (mainlyLn(II) and Ln(III)) now known. Bunzli and Piguetshow how lanthanides can be involved in polymetallicassemblies thanks to polydentate ligands and su-pramolecular chemistry. The authors emphasize theimportance of lanthanide ions as optical spectroscopicor magnetic probes for various applications. Mitchelland Ibers review the area of mixed rare-earth transi-tion-metal chalcogenides which have been character-ized by single-crystal diffraction methods, whileArndt and Okuda present the family of mono(cyclo-pentadienyl) rare-earth complexes together with ap-plications in homogeneous catalysis. Parker, Dickins,Puschmann, Crossland, and Howard examine thestructure and various aspects of the photochemistryor chiroptical properties of lanthanide complexes inaqueous solution. Wickleder concentrates on inor-ganic lanthanide compounds (devoid of organicligands) involving complex anions and provides manyX-ray single-crystal structures.

The second group of articles (organic transforma-tions controlled by lanthanide derivatives) includespapers which remain mainly oriented toward coor-dination chemistry or which are basically concernedby the efficiency and selectivity of organic transfor-mations. Bochkarev details the synthesis and iden-tification of arene-lanthanide compounds (Sc and Yare also included) as well as their chemical reactivi-ties. The divalent lanthanide derivatives are widelyused in organic synthesis, especially diiodosamarium,a reagent that we introduced in organic chemistrymore than 20 years ago (J. Am. Chem. Soc. 1980, 102,2693). Since several reviews in this journal havesummarized recent developments (Chem. Rev. 1992,92, 29; Chem. Rev. 1996, 96, 307; Chem. Rev. 1999,99, 745), it was decided not to include this importantarea in this special issue. Evans and Davis presentthe chemistry of (Me5C5)3Ln complexes, a quite newchemistry, as until 1991 it was believed these com-pounds could not exist. Marques, Sella, and Takatssimilarly discuss the structure and chemistry ofdivalent and trivalent lanthanide complexes involv-ing pyrazolylborate ligands. Catalysis by lanthanidecomplexes is a highly promising area that is coveredby four contributions. Molander and Romero showthe importance of lanthanocene catalysts to performselective organic synthesis. This paper is organizedby reaction types (hydrogenation, hydrosilylation,hydroboration, etc.). Shibasaki and Yoshikawa de-scribe for various enantioselective reactions the widescope of bifunctional asymmetric lanthanide(III)catalysts, mostly heterobimetallic complexes basedon lanthanide and alkali metal. Chiral lanthanidecatalysts giving rise to asymmetric amplifications(nonlinear effect) are reviewed by Inanaga, Furuno,and Hayano. Kobayashi, Sugiura, Kitagawa, andLam explore the numerous developments in catalyticorganic synthesis arising from the Lewis-acid proper-ties of rare-earth metal triflates.

The third group of contributions is devoted to manydifferent kinds of materials or sensors using lan-thanide components. Binnemans and Gorller-Wal-rand present the synthesis, structure, and physicalproperties of liquid crystals and surfactants contain-ing lanthanides. Kuriki, Koike, and Okamoto reviewthe use of lanthanide complexes in optical fiber lasers

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and amplifiers, while the paper by Kido and Okamotois devoted to electroluminescent materials based onorganolanthanide complexes. Benelli and Gatteschidiscuss the magnetism of lanthanides in molecularmaterials with transition-metal ions and organicradicals. Properties of lanthanide complexes are veryuseful in molecular recognition and chirality sensingof biological substrates, as explained by Tsukube andShinoda. Adachi, Imanaka, and Tamura review thetopic of ionic conductive lanthanide oxides. Lombardiand Davis present the periodic properties of forceconstants of small transition-metal and lanthanideclusters. Finally, Adam discusses the interest oflanthanide components in non-oxide glasses.

The present importance of lanthanides is clearlyevidenced by the rich and diversified chemistry whichhas been reviewed by 50 authors and co-authors,generating 3700 references and notes, and 670 printedpages. The multidisciplinary character of lanthanide

research is well illustrated in this special thematicissue, since the topics range from inorganic andorganometallic chemistry through organic chemistryand from physics to biology. Moreover, lanthanidesremain very topical in material sciences. It is ex-pected that this thematic issue will stimulate re-search in all of these areas, where we can expectmany more exciting discoveries. The guest editorthanks the authors for having agreed to participatein this enterprise and for their excellent contribu-tions. He also thanks Professor Gladysz and Ms.Haltrich from Chemical Reviews for their kind andefficient support.

Henri B. KaganInstitut de Chimie Moleculaire d'Orsay

Universite Paris-Sud, OrsayCR020014I

1806 Chemical Reviews, 2002, Vol. 102, No. 6 Editorial