Rare earth metal amides

Keywords bis(trimethylsilylamides), hypersilyl, rare earth metal amides, rare earth metal silyls... 

Wu and coworkers prepared a new diamide ligand LSI with a CH2SiMc2 bridging unit and a series of rare-earth metal complexes supported by LSI. Diamide complexes [Ln(LSl) N(SiMe3)2 (THF)] (Ln = Y (222), Nd (223), Sm (224), Dy (22S), Yb (226)) were obtained from the reaction of H2LSI with 1 equiv of corresponding rare-earth metal amide complexes [Ln N(SiMc3)2 3( J.-Cl)Li(THF)3] in toluene (Scheme 82) [167]. 

Y. Wu, S. Wang, L. Zhang, G. Yang, X. Zhu, C. Liu, C. Yin, J. Rong, Efficient guanylation of aromatic and heterocyclic amines catalyzed by cyclopentadienyl-free rare earth metal amides. Inorg. Chim. Acta 362, 2009 2814. 

Immobilization of Rare-Earth Metal (Silyl)amide Complexes... 

Like the amide derivatives (see Sect. 6), rare-earth metal alkoxide (aryl-oxide) complexes Ln(()R)x are pseudo-organometallics exhibiting a Ln-... 

Most of the knowledge about aluminate and alkylaluminum coordination stems from X-ray crystallographic studies. The basic idea of this section is to compile a rare-earth metal aluminate library categorizing this meanwhile comprehensive class of heterobimetallic compounds. Main classification criteria are the type of homo- and heterobridging aluminate ligand (tetra-, tri-, di-, and mono alkylaluminum complexes), the type of co-ligand (cyclopen-tadienyl, carboxylate, alkoxide, siloxide, amide), and the Ln center oxidation state. In addition, related Ln/Al heterobimetallic alkoxide complexes ( non-alkylaluminum complexes) are surveyed. Emphasis is not put on wordy structure discussions but on the different coordination modes (charts) and important structural parameters in tabular form. An arbitrary collection of molecular structure drawings complements this structural report. 

The silyl amide type ligands have been used extensively in rare earth chemistry, as well as in actinide and transition metal chemistry, to stabilize electronically unsaturated metal centers due to the available lone pair on the nitrogen donor atom. Because of the relatively larger steric encumbrance, the rare earth complexes with silyl amide type ligands often exhibit low coordination numbers. As a consequence, the large and electropositive rare earth metal centers are accessible to external reagents, which make them more active in many reactions. 

Bambirra, S., van Leusen, D., Tazelaar, C.GJ. et al. (2007) Rare earth metal alkyl complexes with methyl-substituted triazacyclononane-amide ligands ligand variation and ethylene polymerization catalysis. Organometallics, 26, 1014. 

The resting state of the catalyst is believed to be an amine adduct of the catalytic active Ln-amide. For lanthanocene catalysts such an amido amine species of the type Cp 2Ln(NFiR)(NH2R) has been spectroscopically and crystallographically characterized [103]. Amines, coordinating solvents and other external bases may adversely affect the reactivity of the rare-earth metal center, in particular if the metal center is readily accessible. Sterically open anya-lanthanocenes and constrained-geometry catalysts (CGC) [27,104,108] and more recently also sterically readily accessible nonmetallocene catalysts [101,115,116] have displayed product inhibition (leading to apparent first-order kinetics) or substrate inhibition (resulting in self-acceleration). 

Hydroamination/bicyclization of aminodialkenes, aminodialkynes, and amino-alkenynes opens a straightforward route to pyrrolizidines and indolizidines in a tandem C-N and C-C bond forming process. An important prerequisite for the success of this reaction sequence is a sufficient lifetime of the rare-earth metal alkyl intermediate formed in the initial insertion process of the alkene/alkyne in the Ln-amide bond in order to permit the carbocyclization step (Scheme 9) [99,174],... 

Fig-1. Rare earth metal reagents in organic synthesis (NTf2=bis [trifluoromethyl)sulfonyl] amide, (-)BNP=(J )-(-)-l,l -binaphthyl-2,2 -diylphosphato)... 

The formation of anionic rare earth metal ligand moieties or ate complexation are commonly observed features of salt metathesis reactions when alkali metal cyclopentadienyl [147], alkyl [96], amide [97,255] and alkoxide derivatives are employed [Eqs. (39)-(42)] [256]. 

The direct aldol reaction of carboxylic acid derivatives and aldehydes (or ketones) is very difficult. Recently, Kobayashi and co-workers (146) extended the ketones to amides as suitable candidates successfully for the direct aldol reaction. The screening of metal sources revealed that Ba(0-tBu)2 was the better catalyst than Sr(0-iPr)2, Ca(0-iPr)2, or Mg(0-iPr)2, whereas rare earth metals (eg, La(0-iPrls) are catalytically inactive in the presence of p-methoxyphenol. In this aldol reaction, barium enolate formed in situ from barium alkoxide and acylamide and... 

Schadle D, Maichle-Mossmer C, Schadle C, Anwander R. Rare earth-metal methyl, amide and imide complexes supported by a superbidky scorpionate ligands. Chem Eur J. 2015 21 662-670. 

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