Synthesis and structural study of a lithium complex of 6-methyl-2-(trimethylsilylamino)pyridine and its use in the formation of some lanthanoid complexes

Lithiation of 6-methyl-2-(trimethylsilylamino)pyridine (APyTMSH) occurs smoothly in tetrahydrofuran (thf) affording [Li(APyTMS)(thf)]2 (1). Treatment of anhydrous lanthanoid chlorides (LnCl3, Ln=Gd, Er) with 1.5 equivalents of (1) yields the solvent-free homoleptic tris–amido complexes [Ln(APyTMS)3], (Ln=Gd (2); Ln=Er (3)). Similar treatment of LnCl3 (Ln=Gd, Er) with one equivalents of 1 putatively generates the heteroleptic species [Ln(APyTMS)2Cl], (Ln=Gd (4); Ln=Er (5)) in situ, however, these compounds undergo redistribution in hexane to yield homoleptic 2 and 3 and the anhydrous lanthanoid halides (Ln=Gd, (6), Ln=Er (7)) and were therefore not fully characterised. These lanthanoid reagents are extremely moisture sensitive as examplified by the low yield isolation of [APyH2·H]2[ErCl5(thf)] during one prepartion of 3. The structures of compounds 1, 2, 3 and 8 were characterised by X-ray crystallographic methods. The X-ray structure of 1 is a centrosymmetric dimer similar to its diethyl ether analogue. Compounds 2 and 3 are six-coordinate homoleptic mononuclear species and compound 8 comprises the unprecedented [ErCl5(thf)]− anion within an intricate hydrogen-bonded ionic system.