Bis(1°-amino)cyclodistib(III)azanes:  the First Structural Characterization of cis and trans Isomers of a Single Cyclodipnict(III)azane

The dichlorocyclodistib(III)azane [ClSb(μ-N^tBu)]₂ (1) has been shown to exist as the cis isomer in the solid state. A series of bis(1°-amino)cyclodistib(III)azanes [R‘NHSb(μ-N^tBu)]₂ (2, R‘ = ^tBu; 3, R‘ = Dipp; 4, R‘ = Dmp) has been prepared by the reaction of 1 with 2 equiv. of LiNHR‘. On the basis of NMR solution spectra, all three derivatives are formed as a mixture of cis and trans isomers. In the case of 3, the structures of both the cis and trans isomers have been determined by X-ray crystallography; cis-3 adopts an endo, endo arrangement for the amido protons of the DippNH groups. Isomerization of trans-3 into cis-3 occurs slowly in solution. Deprotonation of 2 with 2 equiv. of ⁿBuNa or trans-3 with ⁿBuLi produces [Na₂Sb₂(μ-N^tBu)₄] (5) and [Li₂Sb₂(μ-N^tBu)₂(μ-NDipp)₂] (6), whose solvated cubane structures were established by X-ray crystallography. In contrast, the reaction of cis-3 with 2 equiv. of ⁿBuLi produces the tricyclic compound [Li₂Sb(μ-N^tBu)₂(μ-NDipp)(μ-NHDipp)] (7).