Synthesis and characterization of pyridine-capped oligoazine-bridged ruthenium dimers

A series of pyridine capped oligoazines have been synthesized and characterized by infrared, proton NMR and electronic spectroscopies. The ground state probes indicate limited conjugation length, about one repeat unit. Electronic spectroscopy indicates that the conjugation length in the excited state increases to about three repeat units. Excited state data also shows that the position of the azine centered $\pi \to\ \pi\sp*$ transition has an x$\sp{-1}$ dependence, where x is the number of repeat units. The oligoazines were then complexed to bis-(bipyridine)Ru$\sp{+2}$ in a 2:1 stoichiometry where the oligoazine acted as a bridge between the two ruthenium centers. The metal dimers were characterized by infrared and electronic spectroscopies. Chemical oxidation of the ruthenium dimers from the +4 to +5 state was attempted in order to generate a series of analogous complexes which exhibited an intravalence charge transfer. The goal was to define some of the parameters that influence this kind of charge transfer. However upon oxidation of the fully reduced species oxidation occurred an the terminal imine, rather than the metal, where complexation to the ruthenium occurs, and formed a lactam. This broke the conjugation of the system and precluded the possibility of observing the intervalence charge transfer