Bulky Amido Ligands in Rare Earth Chemistry — Syntheses, Structures, and Catalysis

Abstract

The amido metal chemistry of the rare earth elements is a rapid developing area in coordination chemistry. Especially bulky mono and bidentate amido and amidinates have been introduced as ligands in rare earth chemistry. Due to these sterically demanding ligands, the coordination numbers of the rare earth elements are significantly reduced. This article focuses on two of these bulky ligand systems: bis(trimethylsilyl)amide and aminotroponiminates. The homoleptic bis(trimethylsilyl)amides of rare earth elements, [Ln{N(SiMe3)2}3], are well established compounds in synthetic chemistry. Therefore, this article reviews recent progress in the catalytic application of these compounds. In the second part of this research report, it is shown that N, N′‐disubstituted aminotroponiminates and mono bridged bisaminotroponiminates can be used as cyclopentadienyl alternatives. Achiral and chiral aminotroponiminates have been used. The structural properties, reactivities as well as the catalytic and synthetic applications of the aminotroponiminates complexes will be outlined in this article.

New Perspectives for Aminotroponiminates: Coordination Chemistry, Redox Behavior, Cooperativity, and Catalysis

“…In this context, the lithium complex Li(ATI Ph/Ph ) should be mentioned, since an unusual Li–Ph contact was detected for this compound in the solid state (Figure b, bottom) . Finally, bridged ATIs and tropocoronands should formally also be mentioned in the category of ATI ligands with additional donor groups at N (Figure c) …”

“…ATI complexes have been intensively investigated as catalysts in hydroamination reactions with a strong focus on lanthanoid and zinc compounds. These fields of research have been covered in recent review articles , , . Thus, only more recent advances and contributions based on ATI complexes of other elements are included here.…”

“…[16] After initial reports on the functionalization of the C 7 ligand backbone in the 5-position via electrophilic aromatic substitution, [17,18] this type of reaction has recently been investigated in further detail. [19][20][21][22][23] Bromination proceeds smoothly and in excellent yields (90 %), [17,18,[20][21][22] while other substituents can be introduced only with lower yields of 19-43 % [Scheme 3, E = Br, I, N 2 Aryl, NO 2 , COMe, C 2 (CN) 3 ]. [19,22,24] The bromo-substituted compound 9-Br can be subjected to nucleophilic aromatic substitution to give 10-Nu in excellent yields (92-99 %) {Scheme 3: Nu = SPh, S[3,5-C 6 H 3 (CF 3 ) 2 ], SePh, TePh; Nu = S(O)Ph with one additional step}.…”

“…[34] Finally, bridged ATIs and tropocoronands should formally also be mentioned in the category of ATI ligands with additional donor groups at N (Figure 8c). [2][3][4][52][53][54][55][56][57] Figure 8. Examples of (a) H-ATI ligands that bear donor functionalities in the substituents at the N ATI atoms; (b) ATI complexes with substituents at N ATI atoms that are involved in donor···M interactions; (c) bridged ATIs and tropocoronands.…”

“…They are distinguished from these types of ligands by a rigid C 7 ligand backbone, which is a prominent structural feature of the ATI ligand family. ATIs have found application in the stabilization of cationic group 13 complexes, as substitutes for cyclopentadienide ligands in lanthanoid chemistry,, for the synthesis of hyper‐ and hypo‐valent group 14 compounds,, in the investigation of spin delocalization of first row‐transition metal complexes, and in hydroamination catalysis . These fields have been covered elsewhere by the cited review articles.…”