Syntheses and Structures of [Sn{NR}2{Sn(μ-NMe2)}2]:  Model Intermediates in the Formation of Imido Group 14 Cages and Rings [R = 2,6-Pr i 2C6H3 (Dipp), 2,4,6-Me3C6H2 (Mes)]

The 1:1 reactions of aliphatic primary amines [RNH2] with [Sn(NMe2)2] yield the imido Sn(II) cubanes [SnNR]4; however, for highly sterically crowded amines this reaction is retarded and the model intermediates [Sn{NR}2{Sn(μ-NMe2)}2] [R = 2,6-Pr i C6H3 (Dipp) (1), 2,4,6-Me3C6H2 (Mes) (2)] can be isolated. The latter indicate that the formation of imido cubanes and trimers from the metalation reactions of primary amines with a range of group 14 precursors may occur via a common reaction sequence involving stepwise metalation. The low-temperature X-ray structures of 1 and 2 show them to have similar [Sn3N4] cage arrangements consisting of a planar {Sn(NR)2} unit straddling a {Sn(μ-NMe2)}2 ring. No intermolecular association occurs in the solid-state structure of 1. However, the reduced steric demands of the Mes groups in 2 lead to a complicated three-dimensional network consisting of fused hexameric units linked by Sn···Sn interactions.