Structural Patterns and Forms of Aggregation of Metallated Diamido Donor Ligands upon Going from Lithium to Thallium(I)

Two polyfunctional lithium amides, [(2-C5H4N)C(CH3){CH2N(Li)SiMe2R}2]2 [R = Me (3), tBu (4)], have been synthesized and structurally characterized by X-ray crystallography. They were found to have dimeric structures containing ladder-type Li−N arrangements in which the form of aggregation and thus folding of the ladder appears to be influenced by the steric demand of the N-bonded silyl groups. Substitution of the lithium ions by thallium(I) was achieved in two steps, yielding the mixed metal amide [(2-C5H4N)C(CH3){CH2N(Li)SiMe3}{CH2N(Tl)SiMe3}]2 (5) and the thallium(I) diamide [(2-C5H4N)C(CH3){CH2N(Tl)SiMe3}2]2 (6). X-ray diffraction studies of both compounds revealed a dimeric ring structure through Li−N links for the former, while the latter is monomeric and only weakly aggregated in the crystal structure through a short, unsupported thallium(I)−thallium(I) contact of 3.500(2) A.