N-Heterocyclic Germylenes: Structural Characterisation of Some Heavy Analogues of the Ubiquitous N-Heterocyclic Carbenes

Abstract EN

The X-ray crystal structures of three N-heterocyclic germylenes (NHGes) have been elucidated including the previously unknown 1,3-bis(2,6-dimethylphenyl)diazagermol-2-ylidene (1).

In addition, the X-ray crystal structures of the previously synthesised 1,3-bis(2,4,6-trimethylphenyl)diazagermol-2-ylidene (2) and 1,3-bis(2,6-diisopropylphenyl)diazagermol-2-ylidene (3) are also reported.

The discrete molecular structures of compounds 1 to 3 are comparable, with Ge-N bond lengths in the range 1.835-1.875 Å, while the N-Ge-N bond angles range between 83.6 and 85.2°.

Compound 2 was compared to the analogous N-heterocyclic carbene species, 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene (IMes).

The major geometrical difference observed, as expected, was the bond angle around the divalent group 14 atom.

The N-Ge-N bond angle was 83.6° for compound 2 versus the N-C-N bond angle of 101.4° for IMes.

The Sn equivalent of (1), 1,3-bis(2,6-dimethylphenyl)diazastannol-2-ylidene (4), has also been synthesised and its crystal structure is reported here.

In order to test their suitability as ligands, compounds 1 to 3 were reacted with a wide range of transition metal complexes.

No NHGes containing metal complexes were observed.

In all cases the NHGe either degraded or gave no reaction.