Alkoxycarbonyl substituted ruthenium mono(bipyridine) complexes: steric effects of the bipyridine substituents

Mono(bipyridine) complexes of ruthenium (n,n′-L2-2,2′-bpy)Ru(CO)2Cl2 (n=3, 4, 5, or 6; L=CO(O)Me or CO(O)Et) were synthesised and structurally characterised. The steric effects of the substituents L on the geometry and the energetics of the compounds were studied using both experimental and theoretical methods to clarify the effect of substituent position on complex behaviour and electrochemical properties. Calculations were carried out with the density functional hybrid B3PW91 method. The position of the substituent was found to strongly effect the geometry and the energy of the mono(bipyridine) complexes. Alkoxycarbonyl substituents at 3,3′- and 6,6′-positions caused strong structural distortion of the complexes. The strain caused by 6,6′-substituents was readily relaxed forming new chelating complex with tridentate ligand coordination. Varying the bipyridine substituent position also caused changes in the electrochemical properties of the compounds reflected by the variations in the HOMO–LUMO energy gap. Ligand modifications caused by changing the substituent locations offer possibilities to design complexes with the required structural or electrochemical properties.