Electrochemical polymerisation studies of aza-15-crown-5 vinyl-2,2'-bipyridine ruthenium(II) complexes

The electrochemical polymerisation of the mono(ligand) and tris(ligand) ruthenium(II) complexes, [RuL(1,2)(bipy)(2)](2+) and [RuL(3)(1,2)](2+) (bipy = 2,2'-bipyridine, L(1) = 4-methyl-4'-(N-styryl-aza-15-crown-5)-2,2'-bipyridine, L(2) = 4,4'-bis(N-styryl-aza-15-crown-5)-2,2'bipyridine), has been investigated in acetonitrile. Preparation of electroactive polymer films was established on reductive electropolymerisation of the tris(ligand) ruthenium(II) complexes. Electropolymerisation of [RuL(1)(bipy)(2)](2+) did not take place, suggesting that the polymer formation mechanism involves radical-radical hydrodimerisation for pairs of vinyl groups rather than 'polyvinyl-type' chain propagation. Lack of electropolymerisation for [RuL(2)(bipy)(2)](2+), with two vinyl linkages on the same ligand, is explained by steric constraints preventing repeated linkages between aza-15-crown-5 vinyl-pyridine units. While polymer formation via the alternative route of oxidative coupling of the N-styryl-aza-15-crown-5 moieties might be anticipated, electro-oxidation for the [RuL(2)(bipy)(2)](2+) and [RuL(3)(1,2)](2+) complexes led only to the formation of electroinactive orange films with concurrent electrode passivation.