Photoinduced synthesis and electrochemical properties of new ruthenium(mono)bipyridine dialkylcyanamide and propiononitrile complexes

Photochemical exchange of carbonyls was used to produce new ruthenium dialkylcyanamide and nitrile compounds RuCl₂(bpy)(CO)(NCNMe₂)] (2), RuCl₂(bpy)(CO)(NCNEt₂)] (3), and RuCl₂(bpy)(CO)(NCEt)] (4) from trans(Cl)-RuCl₂(bpy)(CO)₂] (1). The reaction energetics, steric effects and electronic effects induced by the dialkylcyanamide and nitrile ligands were studied using computational DFT methods and cyclic voltammetry. In all cases the photochemical exchange reaction favors rearrangement of the ligands and formation of the trans(Cl,L)-RuCl₂(bpy)(CO)L] (L = NCNMe₂, NCNEt₂ or NCEt) isomer as the main products. The oxidation potential of the complexes decreases with the increase of the HOMO energy and of net electron-donor character of the ligands, the dialkylcyanamides (whose electrochemical Lever E_L ligand parameter has been estimated) behaving as stronger net electron donors than propiononitrile or CO. The electronic effect of the dialkylcyanamide and nitrile ligands is also reflected into the HOMO-LUMO energy difference, which is slightly reduced compared to the original dicarbonyl compound 1. The computational results show that the geometry of the isomer plays also an important role in the determination of orbital energies.