Synthesis, characterization and electrochemistry of bis(3-aryl-6,6-dimethylcyclohexadienyl)ruthenium complexes

Five bis(3-aryl-6,6-dimethylcyclohexadienyl)ruthenium complexes (4a-4e) are prepared by reactions between di-μ-chlorodichlorobis(1-3η:6-8η)-2,7-dimethyl-octadienyl]diruthenium and the corresponding dienes. The larger aryl substituents increase the barrier to rotation in 4a-4e relative to bis(3-methyl-6,6-cyclohexadienyl)ruthenium (5b). The activation parameters were determined by line-shape analysis for the exchange process in 4a: ΔG^† (183 K), 8.0 ± 0.2 kcal/mol; ΔH^†, 10.3 kcal/mol; and ΔS^†, 13 cal/mol/K. The electronic effect of the aryl substituents on the cyclohexadienyl ligand on the oxidation potential of the complex are compared to the effect of methyl substituents.