Unsaturated Systems and Biradicals

Investigations of unsaturated group 14 element-nitrogen ring systems are primarily focused on cyclic oligomers of the type ( MNR) in which M is in the divalent state. The six-membered rings ( = 3) are potentially Hiickel six 7i-electron systems in which each of the nitrogens contribute two 71-electrons. 

Examples of this class of inorganic heterocycle are limited to germanium. Both four- and six-membered rings have been characterised with the ring size being determined by the nature of the substituent on the nitrogen atoms.  

With less bulky groups on the nitrogen atoms, the most common oligomer formed by the hypothetical monomeric group 14 imides, M=NR (M = Ge, Sn, Pb), is the cubic tetramer, e.g. [M()i3-N Bu)]4. This is especially true for the heavier (larger) elements tin and lead for which, in contrast to germanium, cubanes are observed even when R = 2,6- Pr2C6H3.  

The M2N2 rings in 10.31 and 10.32 are both planar with the groups attached to the group 14 metal centres (aryl and Cl, respectively) in a trans arrangement 

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