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-NtBu)]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-NtBu)]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-NtBu)4] (5) and [Li2Sb2(μ-NtBu)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-NtBu)2(μ-NDipp)(μ-NHDipp)] (7).