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 conta ining ladder-type Li-N arrangements in which the form of aggregation and th us folding of the ladder appears to be influenced by the steric demand of t he N-bonded silyl groups. Substitution of the lithium ions by thallium(I) w as 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 compou nds revealed a dimeric ring structure through Li-N links for the former, wh ile the latter is monomeric and only weakly aggregated in the crystal struc ture through a short, unsupported thallium(I)-thallium(I) contact of 3.500( 2) Angstrom.