Rare-Earth-Metal Methyl, Amide, and Imide Complexes Supported by a Superbulky Scorpionate Ligand

The reaction of monomeric [(TptBu,Me)LuMe2] (TptBu,Me=tris(3‐Me‐5‐tBu‐pyrazolyl)borate) with primary aliphatic amines H2NR (R=tBu, Ad=adamantyl) led to lutetium methyl primary amide complexes [(TptBu,Me)LuMe(NHR)], the solid‐state structures of which were determined by XRD analyses. The mixed methyl/tetramethylaluminate compounds [(TptBu,Me)LnMe({μ2‐Me}AlMe3)] (Ln=Y, Ho) reacted selectively and in high yield with H2NR, according to methane elimination, to afford heterobimetallic complexes: [(TptBu,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 1H and 13C NMR spectroscopic studies at variable temperatures and 1H–89Y HSQC NMR spectroscopy. Treatment of [(TptBu,Me)LnMe(AlMe4)] with H2NtBu gave dimethyl compounds [(TptBu,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 [(TptBu,Me)LnMe2] (Ln=Y, Ho, Lu) were made accessible through aluminate cleavage of [(TptBu,Me)LnMe(AlMe4)] with N,N,N′,N′‐tetramethylethylenediamine (tmeda). The solid‐state structures of [(TptBu,Me)HoMe(AlMe4)] and [(TptBu,Me)HoMe2] were analyzed by XRD. Organoaluminum‐assisted deprotonation of primary amines affords mono‐rare‐earth imide complexes [(TptBu,Me)Ln(NR)(AlMe3)] (Ln=Y, Ho) supported by a tridentate scorpionate ligand (see scheme). In contrast, organoaluminum‐free dimethyl precursor [(TptBu,Me)LuMe2] yields mixed amide/methyl complexes of the type [(TptBu,Me)Lu(HNR)(Me)].