Aromaticity or non aromaticity in germanazenes? Theoretical studies on germanazenes, the N-cyano analogs and their carbodiimide isomers

Theoretical studies of germanazene rings [(GeII–NR)2,3; R = H, Me, CN, Ph] have been performed at the DFT/B3LYP level. The fully optimized geometrical structures display four or six-membered planar rings of alternating germanium and nitrogen, in good agreement with the available X-ray experimental data. The hypothetical molecule (GeN–H)2 presents only a small distortion from planarity. Although the planar conformation could indicate some degree of delocalization, the stabilization energy – estimated using the concept of homodesmotic reactions – indicates very little or no aromatic character in these molecules. The easy experimental formation of these germanazenes can be explained by di- (or tri-)merisation of the transient monomeric germylene-imine Gedouble bond; length as m-dashNR in its triplet state. When R = CN, in conformity with the experimental results, the most stable species is the isomeric carbodiimide form (Gesingle bondNdouble bond; length as m-dashCdouble bond; length as m-dashN)n, a result which is easily explained by the maximum spin density on the terminal nitrogen in the calculated monomer.