Novel synthesis and characterisation of ruthenium tris (4-methyl-4′-vinyl-2,2′-bipyridine) complexes

The synthesis of the ligand 4-methyl-4′-vinyl-2,2′-bipyridine is discussed. Methods previously reported presented problems in terms of yield and purity of a precursor. Traces of starting material (4,4′-dimethyl-2,2′-bipyridine) contaminated the product and this contaminant carried through to the synthesis of 4-methyl-4′-vinyl-2,2′-bipyridine. Thus, upon complexation to form ruthenium tris (4-methyl-4′-vinyl-2,2′-bipyridine) bis (hexafluorophosphate), the bis-, mono- and non-vinyl complexes were also present. Electropolymerisation of ruthenium tris (4-methyl-4′-vinyl-2,2′-bipyridine) bis (hexafluorophosphate) to produce a high quality polymer film requires the maximum number of vinyl ligands per molecule of complex. The relative percentages of complexes within the mixture can be calculated using proton NMR. This method is based upon the integration values of the vinyl resonances of the tris- and bis-compounds. However, a simple mathematical model has been developed that can predict the percentage composition of the mixture prior to complexation by taking into account the purity of 4-methyl-4′-vinyl-2,2′-bipyridine. The novel syntheses of 4-(2-hydroxypropyl)-4′-methyl-2,2′-bipyridine, 4-methyl-4′-(E-prop-2-enyl)-2,2′-bipyridine and ruthenium tris (4-methyl-4′-(E-prop-2-enyl-2,2′-bipyridine) bis (hexafluorophosphate) are also described. Full spectral data for all compounds, together with novel data for ruthenium tris (4-methyl-4′-vinyl-2,2′-bipyridine) bis (hexafluorophosphate), are reported.