Rare earth metal complexes catalytic applications

Catalytic applications of organo-rare-earth metal complexes reported prior to 2002 are summarized in two excellent reviews [19,20] and, therefore, will not be discussed unless being relevant for understanding of key reaction details. A recent comprehensive review on theoretical analyses of organo-rare-earth metal-mediated catalytic reactions is available [17], Although o-bond metathesis plays a pivotal role in many rare-earth metal-catalyzed polymerizations, the discussion of these processes is beyond the scope of this review and the interested reader may consult one of the pertaining reviews [21-24],... 

Following the exploration of many catalytic applications in the rare-earth metal complexes containing L24, Lappert and coworkers recently described the... 

Only a few tris-P-diketiminato rare-earth metal complexes (74,75, and 77) were prepared [64,71,72] and no catalytic activities were reported until Shen and coworkers very recent discovery on synthesis and catalytic applications of such complexes [86], To compare the electronic effects of ligands on the reactivity of their lanthanide complexes, L21 and its derivatives L28 (a methyl electron-donating group at the para-position on the phenyl) and L29 (a chloro electron-withdrawing group at the para-position on the phenyl) were used in the study. LnCb (Ln = Pr, Nd, Sm) and lithium salt of L29 via salt elimination led to [Ln(L29)3] (Ln = Pr (130), Nd (131), Sm (132)). [Nd(L21)3] (133) and [Nd(L28)3] (134) were prepared by the same method shown in Scheme 45. 

This book contains four chapters in which part of the recent development of the use of molecular rare-earth metal compounds in catalysis is covered. To keep the book within the given page limit, not all aspects could be reviewed in detail. For example, the use of molecular rare-earth metal complexes as Lewis acidic catalysts is not discussed in this book. The first two chapters review different catalytic conversions, namely the catalytic o-bond metathesis (Chapter by Reznichenko and Hultzsch) and the polymerization of 1,3-conjugated dienes (Chapter by Zhang et al.). Within these chapters, different catalytic systems and applications are discussed. The final two chapters are more concentrated on recent developments of... 

The chemistry of organometallic group 4 metal compounds is well developed, thanks to their importance in polyolefin synthesis. Hence, their application in catalytic asymmetric hydroamination reactions is highly desirable. Group 4 metal complexes are commonly less sensitive and easier to prepare than rare earth metal complexes. Most important of all, many potential precatalysts or catalyst precursors are com mercially available. 

Pyrochlores - The pyrochlores are a group of materials with the general formula A2B2O7. They have been mentioned as a material for catalytic combustion. The structure allows vacancy at the A site and the O sites to some extend. The A position can be a rare earth metal or an element with lone pair of electrons and the B position can be a transition metal or a post-transition metal. This make the structure rather flexible as the oxidation state of the transition metal B can be varied as well as the nature of the A and B metal ions. Subramanian and Castro et al. have prepared several pyrochlores. When studying the thermal stability of different complex oxides, Zwinkels et al. have shown that La2Zr207 pyrochlores have a surface area lower than 5 m g , already after calcination at 1000 °C. Hence, such materials are probably not suitable for high temperature applications unless the preparation method is improved. However, pyrochlore compounds have been patented for catalytic combustion applications, see Section 5.5. 

Progress on unsymmetrical hybrid chiral phosphine—phosphoramidite ligands and their application in asymmetric catalytic reactions 12CJ02239. Rare earth metal oxazoline complexes in asymmetric catalysis 12CC 10587. 

This volume of the Handbook on the Physics and Chemistry of Rare Earths adds five new chapters to the science of rare earths, compiled by researchers renowned in their respective fields. Volume 34 opens with an overview of ternary intermetallic systems containing rare earths, transition metals and indium (Chapter 218) followed by an assessment of up-to-date understanding of the interplay between order, magnetism and superconductivity of intermetallic compounds formed by rare earth and actinide metals (Chapter 219). Switching from metals to complex compounds of rare earths, Chapter 220 is dedicated to molecular stmctural studies using circularly polarized luminescence spectroscopy of lanthanide systems, while Chapter 221 examines rare-earth metal-organic frameworks, also known as coordination polymers, which are expected to have many practical applications in the future. A review discussing remarkable catalytic activity of rare earths in site-selective hydrolysis of deoxyribonucleic acid (DNA) and ribonucleic acid, or RNA (Chapter 222) completes this book. 

Siloxide ligands are able to coordinate to rare earth metals in various oxidation states and coordination numbers to primarily form mono- and dinuclear complexes. In particular, the synthetic and stmctural chemistry of trivalent rare earth siloxides are well documented in the literature and show analogies with rare earth alkoxides. It is fair to state, however, that the field of divalent and tetravalent rare earth siloxides is poorly developed and that applications pertaining to the design of siloxide-based homogeneous and heterogeneous rare earth metal catalysts as well as the development of novel silicate-based materials are scarce. Although the few results of the catalytic activity of some of the rare earth siloxides in olefin... 

The examples discussed so far are all transition metal complexes. As we will see later (Chapters 4-9), most homogeneous catalytic processes are indeed based on transition metal compounds. However, catalytic applications of rare earth complexes have also been reported, although so far there has not been any industrial application. Of special importance are the laboratory-scale uses of lanthanide complexes in alkene polymerization and stereospecific C-C bond formation reactions (see Sections 6.4.3 and 9.5.4). 

Abstract This review deals with the synthesis and the catalytic application of noncyclopentadienyl complexes of the rare-earth elements. The main topics of the review are amido metal complexes with chelating bidentate ligands, which show the most similarities to cyclopentadienyl ligands. Benzamidinates and guanidinates will be reviewed in a separate contribution within this book. Beside the synthesis of the complexes, the broad potential of these compounds in homogeneous catalysis is demonstrated. Most of the reviewed catalytic transformations are either C-C multiple bond transformation such as the hydroamination and hydrosilylation or polymerization reaction of polar and nonpolar monomers. In this area, butadiene and isoprene, ethylene, as well as lactides and lactones were mostly used as monomers. 

For a better understanding of many successful applications of the rare earth-alkali metal containing LnM3tris (binaphthoxide) complexes (LnMB, Ln=rare earth, M=alkali metal) to catalytic asymmetric synthesis, intense investigations also focused on the determination of the structure. It has been shown that these complexes, which can be readily prepared from the corresponding rare earth trichlorides and/or rare earth isopropoxides [5],possess a structure as presented in Fig. 2. This structure was supported by various NMR spectroscopic, MS spectrometric, X-ray crystallographic and other analytic investigations of a variety of LnMB complexes. 

Titanium is one of the most important transition metals used in catalytic enantioselective reactions. Whereas rhodium, palladium, copper and ruthenium are rather rare in Nature, and the depletion of natural resources is evoked for these, titanium does not suffer from lack of availability. In fact, it is the 9th most abundant element on Earth and one of the cheapest transition metals. The products resulting from the hydrolysis of titanium complexes are nontoxic and do not cause any environmental problems. This low toxicity has allowed titanium to be used for multiple applications, including medical uses (prostheses, sun screens, etc.). 

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