Imide complexes [(TptBu,Me)Y(=NC6H3Me2‐2,6)(DMAP)] and [(TptBu,Me)Lu{=NC6H3(CF3)2‐3,5}(DMAP)] were obtained by Lewis base induced methane elimination of the corresponding methyl/anilide complexes, which were synthesized from [(TptBu,Me)LuMe2] and [(TptBu,Me)YMe(GaMe4)], respectively. Terminal Ln=N bonding is evidenced by very short Ln–N distances [min. 1.993(5) Å] and almost linear Ln–N–C(aryl) bond angles.
The reaction of monomeric [(Tp(tBu,Me) )LuMe2 ] (Tp(tBu,Me) =tris(3-Me-5-tBu-pyrazolyl)borate) with primary aliphatic amines H2 NR (R=tBu, Ad=adamantyl) led to lutetium methyl primary amide complexes [(Tp(tBu,Me) )LuMe(NHR)], the solid-state structures of which were determined by XRD analyses. The mixed methyl/tetramethylaluminate compounds [(Tp(tBu,Me) )LnMe({μ2 -Me}AlMe3 )] (Ln=Y, Ho) reacted selectively and in high yield with H2 NR, according to methane elimination, to afford heterobimetallic complexes: [(Tp(tBu,Me) )Ln({μ2 -Me}AlMe2 )(μ2 -NR)] (Ln=Y, Ho). X-ray structure analyses revealed that the monomeric alkylaluminum-supported imide complexes were isostructural, featuring bridging methyl and imido ligands. Deeper insight into the fluxional behavior in solution was gained by (1) H and (13) C NMR spectroscopic studies at variable temperatures and (1) H-(89) Y HSQC NMR spectroscopy. Treatment of [(Tp(tBu,Me) )LnMe(AlMe4 )] with H2 NtBu gave dimethyl compounds [(Tp(tBu,Me) )LnMe2 ] as minor side products for the mid-sized metals yttrium and holmium and in high yield for the smaller lutetium. Preparative-scale amounts of complexes [(Tp(tBu,Me) )LnMe2 ] (Ln=Y, Ho, Lu) were made accessible through aluminate cleavage of [(Tp(tBu,Me) )LnMe(AlMe4 )] with N,N,N',N'-tetramethylethylenediamine (tmeda). The solid-state structures of [(Tp(tBu,Me) )HoMe(AlMe4 )] and [(Tp(tBu,Me) )HoMe2 ] were analyzed by XRD.
Elaborate synthesis schemes pave the way to f-element and group 3 complexes with multiply bonded imido ligands displaying intriguing reactivity.
Compounds combining the large rare-earth-metal (Ln) centers with the smallest anionic ligand, H À (hydrido), continue to pose challenging questions both in fundamental and applied chemistry. [1] The inherent bonding properties in solid-state binary LnH x phases (e.g., causing metallic behavior) as well as in ligand-supported molecular counterparts (revealing unique cluster chemistry, see Supporting Information) have been the focus of extensive research. Moreover, heterobimetallic solid-state materials, such as Ni 5 LaH x , feature approved rechargeable battery components or, such as LnAlH 6 (obtained from LnCl 3 and NaAlH 4 by the release of hydrogen), are discussed as intermediate-temperature hydrogen-storage materials. [2] On the other hand, the quest for soluble molecular hydrides has triggered immense research efforts. In the meantime, mono and dihydrido derivatives "L 2 LnH" and "LLnH 2 " (L = monoanionic ligand), respectively, are assigned a crucial role in a variety of stoichiometric and catalytic transformations, [3] whereas complexes of type [LnH 3 (Do) x ] (Do = neutral donor ligand) are still elusive. While mono hydride complexes can exist as monomers, e.g., [(C 5 H 2 tBu 3 ) 2 CeH], [4] dihydrido species "LLnH 2 ", carrying only one ancillary ligand per lanthanide center, tend to form polynuclear complexes (see Supporting Information) containing as few as two [5] and up to six lanthanide metal centers. [6] Several types of ancillary ligands have been employed in an effort to stabilize complexes of low nuclearity, including sterically demanding cyclopentadienyl derivatives such as C 5 Me 4 SiMe 3[6] tris(pyrazolyl)borato scorpionates, [7] tetraazacycloamido, [8] bis(phosphinophenyl)amido pincer, [5] and pyridylamido [9] ligands as well as chelating diamido ligands (see Supporting Information). [10] However, the synthesis of a monomeric rare-earth-metal dihydride was not successful to date.The group of Takats used the sterically demanding hydrotris(3-tert-butyl-5-methylpyrazolyl)borato ligand (Tp tBu,Me ) to stabilize Ln 2+ centers in species such as alkyls, [11] carbenes, [12] amides, [11b] halides, [11,13] or hydrides [14] and was also able to obtain lanthanide dihydride complexes using the less-bulky dimethyl, diisopropyl, or unsubstituted derivative of the Tp ligand, but reported the formation of a mixture of products for the more bulky Tp tBu,Me ligand
The μ2-imide complexes [Ln(AlMe4)(μ2-Nmes*)] x (mes* = C6H2 tBu3-2,4,6) (Ln = Y, La, Nd, Lu) are synthesized from homoleptic heterobimetallic complexes Ln(AlMe4)3 utilizing two distinct protocols: reaction with 2,4,6-tri-tert-butylaniline in hexane via methane elimination or with potassium (2,4,6-tri-tert-butylphenyl)amide in toluene according to a salt metathesis–protonolysis tandem reaction. Complexes [Ln(AlMe4)(μ2-Nmes*)]2 (Ln = Y, Nd, Lu) revealed isomorphous solid-state structures, featuring an asymmetrically bridged Ln2N2 core with very short Ln–N distances (2.071(1)–2.155(3) Å). In the solid-state structure of the lanthanum derivative similar dimeric subunits assemble as La4Al4 oligomers through μ2-η1:η2-bridging tetramethylaluminato moieties. [La(AlMe4)(μ2-Nmes*)]4 displays La---arene interactions (2.702(6) Å) that are considerably shorter than the La(μ-CH3)aluminato bond lengths.
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 [LnNR] 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.
Donor functionalities drastically affect salt-metathetical methylaluminato–amido exchange reactions in CpRLn(AlMe4)2 by triggering methylaluminate cleavage and C–H bond activation of proximal aliphatic groups.
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