Open-Shell Early Lanthanide Terminal Imides

Abstract

Group 3- and 4f-element organometallic chemistry and reactivity are decisively driven by the rare-earth-metal/lanthanide (Ln) ion size and associated electronegativity/ionicity/Lewis acidity criteria. For these reasons, the synthesis of terminal “unsupported” imides [LnNR] of the smaller, closed-shell Sc­(III), Lu­(III), Y­(III), and increasingly covalent Ce­(IV) has involved distinct reaction protocols while derivatives of the “early” large Ln­(III) have remained elusive. Herein, we report such terminal imides of open-shell lanthanide cations Ce­(III), Nd­(III), and Sm­(III) according to a new reaction protocol. Lewis-acid-stabilized methylidene complexes [Tp tBu,MeLn­(μ3-CH2)­{(μ2-Me)­MMe2}2] (Ln = Ce, Nd, Sm; M = Al, Ga) react with 2,6-di­iso­propyl­aniline (H2NAr iPr) via methane elimination. The formation of arylimide complexes is governed by the Ln­(III) size, the Lewis acidity of the group 13 metal alkyl, steric factors, the presence of a donor solvent, and the sterics and acidity (pK a) of the aromatic amine. Crucially, terminal arylimides [Tp tBu,MeLn­(NAr iPr)­(THF)2] (Ln = Ce, Nd, Sm) are formed only for M = Ga, and for M = Al, the Lewis-acid-stabilized imides [Tp tBu,MeLn­(NAr iPr)­(AlMe3)] (Ln = Ce, Nd, Sm) are persistent. In stark contrast, the [GaMe3]-stabilized imide [Tp tBu,MeLn­(NAr iPr)­(GaMe3)] (Ln = Nd, Sm) is reversibly formed in noncoordinating solvents.

Potential precursors for terminal ytterbium(ii) imide complexes bearing the hydrotris(3-tert-butyl-5-methylpyrazolyl)borato ligand

“…S1 †) with a very broad signal at 4.81 ppm for the BH moiety, which is typical for complexes bearing Tp ligands. 10,17,19 The resonance of the amido proton was detected at 3.78 ppm as a singlet with low intensity. The absence of coordinating thf in complex 1 only marginally affects the chemical shifts in the 1 H NMR spectrum, measured in C 6 D 6 (see ESI †).…”

“…Noteworthy, on . 10 The 1 H-NMR signal of the amido proton of compound 7 was detected at 3.40 ppm, only slightly shifted to lower field compared to the free aniline H 2 NAr iPr (3.21 ppm). Complexes 1 thf (3.78 ppm), 1 (3.83 ppm), and 3 thf (4.13 ppm) display a more pronounced low-field shift of the amido proton, clearly indicating increased negative charge on the amido nitrogen atom.…”

“…Once more, the respective treatment of 3 thf with trimethylgallium revealed a distinct reactivity of the higher group 13 homologue. 10 Other than for the 3 thf /AlMe 3 reaction, adduct Tp tBu,Me Yb(NHAr CF3 )(GaMe 3 ) (7) was the only product and could be readily crystallized as yellow needles in 90% yield (space group P2 1 /c, the formation of putative [Tp tBu,Me Yb (GaMe 4 )] as a co-product was not observed).…”

“…2 In particular, the synthesis and structural characterization of terminal imide complexes [LnvNR] poses a major challenge. [3][4][5][6][7][8][9][10] Primary amido moieties of the type [Ln(NHR)], more specifically anilides [Ln (NHAr)], display crucial imide precursors since they are prone to ultimate deprotonation. Basic reagents MB employed for intermolecular deprotonations comprise n-BuLi, M[N(SiMe 3 ) 2 ] (M = Li, K, Rb, Cs) and trimethylaluminium (Fig.…”

Reactivity of a mixed methyl–aminobenzyl guanidinate lutetium complex towards iPrNCNiPr, CS2 and Ph2PH

“…The last two decades have witnessed ever-increasing interest in organorare-earth-metal imides ([Ln = NR]/[–Ln–NR–] n ), 28 which really started to gain momentum after Chen's discovery of a scandium terminal imide, exploiting a sterically enforced deprotonation of a scandium methyl–anilide complex with DMAP. 29 We have attempted to synthesize a lutetium terminal imide with a similar synthetic strategy.…”