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.

Terminal, nondirectional ionic "multiple" bond interactions between group 15 elements and rare-earth metals (Ln) have remained a challenging target until present. Although reports on terminal imide species have accumulated in the meantime, examples of terminal congeners with the higher homologue phosphorus are yet elusive. Herein, we present the synthesis of the first terminal yttrium organophosphinidene complex, Tp tBu,Me Y(� PC 6 H 3 iPr 2 -2,6)(DMAP) 2 , according to a double-deprotonation sequence previously established for organoimides of the smaller rare-earth metals. Subsequent deprotonation of the primary phosphane H 2 PC 6 H 3 iPr 2 -2,6 (H 2 PAr iPr ) with discrete dimethyl compound Tp tBu,Me YMe 2 in the presence of DMAP under simultaneous methane elimination generated a terminal multiply bonded phosphorus. The primary phosphide intermediates Tp tBu,Me YMe(HPAr iPr ) and Tp tBu,Me YMe(HNPAr iPr )(DMAP) are isolable species and were also obtained and fully characterized for holmium and dysprosium. The Lewis acid-stabilized yttrium phosphinidene Tp tBu,Me Y[(μ 2 -PAr iPr )(μ 2 -Me)AlMe 2 ] was obtained by treatment of H 2 PAr iPr with Tp tBu,Me YMe(AlMe 4 ) but could not be converted into a terminal phosphinidene via cleavage of trimethylaluminum. The corresponding reaction of H 2 PAr iPr with Tp tBu,Me YMe(GaMe 4 ) led to adduct [GaMe 3 (PH 2 Ar iPr )] rather than to the formation of a yttrium phosphinidene. The yttrium−phosphorus interaction in the obtained organophosphide and phosphinidene complexes was scrutinized by 31 P/ 89 Y NMR spectroscopy and DFT calculations, unambiguously supporting the existence of multiple bonding.