Light-Promoted Basic Nitrogen Unmasking in Arene Ruthenium Complexes Derived from Z-configured 2,2'-Azobispyridine.

Two novel 2,2'-azobispyridine derivatives bearing N-dialkylamino substituents at position 4,4' were synthesized and their E-Z photoswitching behavior was characterized by combination of 1H- and 13C-NMR spectroscopy, UV-vis absorption and DFT calculations. Both isomers act as ligands towards arene-Ru(II) centers, leading either to E-configured 5-membered chelates (involving coordination of nitrogen atoms from N=N bond and pyridine) or to the uncommon Z-configured 7-membered chelates (involving coordination of nitrogen atoms from both pyridines). The latter show good stability in the dark, allowing single crystal X-ray diffraction study to be reported here for the first time. All synthesized Z-configured arene-Ru(II) complexes undergo irreversible photo-isomerization to their corresponding E isomers with rearrangement of their coordination pattern; this property was advantageously exploited for the light-promoted unmasking of a basic nitrogen atom of the ligand.