A new procedure for the generation of cationic methyl complexes of rare-earth metals has been developed for yttrium and praseodymium as two examples from the rare-earth series. The reactions of the rare-earth-metal tetramethylaluminates [Ln(AlMe(4))(3)] of yttrium and praseodymium with three differently sized crown ethers in thf, namely [12]crown-4, [15]crown-5 and [18]crown-6, respectively, led to the compounds [YMe([12]crown-4)(2)](2+)[AlMe(4)](-)(2) (1), [PrMe([12]crown-4)(2)](2+)[AlMe(4)](-)(2) (2), [YMe([15]crown-5)(thf)(2)](2+)[AlMe(4)](-)(2) (3), [Pr([15]crown-5)(2)](3+)[AlMe(4)](-)(3) (4), [YMe([18]crown-6)(thf)](2+)[AlMe(4)](-)(2) (5) and [PrMe([18]crown-6)(thf)(2)](2+) [AlMe(4)](-)(2) (6). With the exception of 4, all compounds contain molecular di-cations with a Ln-CH(3) unit bonded to one (3, 4, 6) or two (1, 2) crown-ether molecules. The compounds were characterised by determination of their crystal structures, by elemental analyses and in the case of the yttrium compounds by variable temperature NMR spectroscopy. The latter gives insights into molecular dynamic processes and methyl group exchange between cations and anions in solution.

Conversion of the rare‐earth tetramethylaluminates [Ln(AlMe4)3] with phenylacetylene afforded the homoleptic alkynylaluminates [Ln{(μ‐C≡CPh)2AlMe2}3] [Ln = Ce (1), Er(2)]. The reaction of five equivalents of phenylacetylene with the yttrium aluminate [Y(AlMe4)3] afforded [Y{(μ‐C≡CPh)AlMe3}{(μ‐C≡CPh)2AlMe2}2] (3). The cationic yttrium complex [(TMTAC)2YMe2][AlMe4] (4) (TMTAC = 1, 3,5‐trimethyl‐1, 3,5triazacyclohexane) was reacted with phenylacetylene to give the product [(TMTAC)2Y(C≡CPh)2][Me2Al(C≡CPh)2] (5), in which two methyl groups of each, the cation and the anion, were substituted by phenylacetylide groups. Under the same conditions as for the synthesis of compound 5, the holmium analogue reveals different reactivity in forming a neutral alkynyl complex [(TMTAC)2Ho(C≡CPh)3] (6). The introduction of 1, 8‐diethynylanthracene to 4 leads to a structural very similar complex [(TMTAC)2Ho(μ‐1, 8‐diethynylanthracene)3] (7) and offers the same reactivity as observed for the synthesis of 6. All compounds were characterized by X‐ray diffraction experiments. Compounds 1–3 and 5 were also characterized by NMR and elemental analyses.

Keywords: Lanthanoids / Aluminum / Holmium / Magnetic properties / NMR spectroscopyTris(tetramethylaluminate)s of the lanthanoids cerium (1), holmium (2), and erbium (3) were synthesized by treating lanthanoid amide complexes of the type [Ln(NMe 2 ) 3 (LiCl) 3 ] with an excess amount of AlMe 3 . These compounds were characterized by single-crystal X-ray diffraction, elemental analysis, and NMR spectroscopy. Paramagnetic NMR spectroscopic studies were undertaken to investigate the influence of the compounds on the solvent chemical shifts. NMR parameters for the 1 H, 13 C, and 27 Al nuclei of all the 51 reported lanthanoid tris(tetramethylaluminate)s were measured. The reactions of tris(tetramethylaluminate)s of samarium and holmium with an excess amount of tetrahydrofuran led to [LnMe 2 (thf) 5 ][AlMe 4 ] {Ln = Ho (4), Sm (5)}. NMR spectroscopic investigations of the paramagnetic holmium and samarium methyl compounds (i.e., 4, 5) as well as the known diamagnetic analogue [YMe 2 (thf) 5 ][AlMe 4 ] revealed methyl group exchange processes in solution.

A new class of rare-earth-metal alkynyl complexes has been prepared. The reactions of the tris(tetramethylaluminate)s of lanthanum, praseodymium, samarium, yttrium, holmium, and thulium, [Ln(AlMe₄)₃], with phenylacetylene afforded compounds [Ln{(μ-C≡CPh)₂AlMe₂}₃] (Ln=La (1), Pr (2), Sm (3), Y (4), Ho (5), Tm (6)). All of these compounds have been characterized by NMR spectroscopy, X-ray crystallography, and by elemental analysis. NMR spectroscopic studies of the series of para- magnetic compounds [Ln(AlMe₄)₃] and [Ln{(μ-C≡CPh)₂AlMe₂}₃] have also been performed.

The reactions of Ln(AlMe4)3 (Ln=Ho, Tm) with the crown ether [12]crown-4 yield dicationic methyl rare-earth metal complexes [LnMe([12]crown-4)2][AlMe4]2 (Ln=Ho (1), Tm (2)). The reaction of La(AlMe4)3 with [18]crown-6 in thf affords [LaMe([18]crown-6)(thf)2][AlMe4]2 (3). The compounds have been characterized by X-ray diffraction, 1 and 3 additionally by elemental analyses as well as by 1H and 27Al, and 3 also by 13C NMR spectroscopy