Syntheses and Structural Characterization of the Heavier Alkali-Metal Stannates Bearing the Tripodal Triamino Framework: Structural Trends in the Series of [MeSi{SiMe<sub>2</sub>N(4-CH<sub>3</sub>C<sub>6</sub>H<sub>4</sub>)}<sub>3</sub>Sn][M] (M = Na, K, Rb)
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Treatment of the lithium stannate [MeSi{SiMe2N(4-CH3C6H4)}3SnLi(OEt2)] (1) with AgCl yielded the corresponding distannane [MeSi{SiMe2N(4-CH3C6H4)}3Sn]2 (2) as the product of an oxidative coupling in good yield. The distannane (2) underwent reductive cleavage with the heavier alkali metals (sodium, potassium, rubidium) in a non-coordinating solvent (toluene or cyclohexane), to afford the solvate-free stannates(II) [MeSi{SiMe2N(4-CH3C6H4)}3Sn][M] (M = Na (3), K (4), and Rb (5)), which were structurally characterized. The Na atom in 3 is directly bonded to two of the three amido-N atoms of the stannate cage and additionally solvated by π-coordination of a tolyl substituent of a neighboring stannate cage. In contrast, the group 1 metal cations in the two isomorphous compounds 4 and 5 are further removed from the nitrogen functions and are π-coordinated by three tolyl arene rings. The Sn−K distances in 4 were found to be 3.635 and 3.870 Å, whereas the Sn−Rb contacts in 5 are 3.708 and 3.908 Å; these are the first such Sn−Rb bonding contacts to be characterized in a molecular compound by X-ray diffraction.
