Density functional theory calculations on oxidative C-C bond cleavage and N-O bond formation of [Ru(II)(bpy)2(diamine)](2+) via reactive ruthenium imide intermediates.

DFT calculations are performed on [Ru(II)(bpy)2(tmen)](2+) (M1, tmen = 2,3-dimethyl-2,3-butanediamine) and [Ru(II)(bpy)2(heda)](2+) (M2, head = 2,5-dimethyl-2,5-hexanediamine), and on the oxidation reactions of M1 to give the C-C bond cleavage product [Ru(II)(bpy)2(NH=CMe2)2](2+) (M3) and the N-O bond formation product [Ru(II)(bpy)2(ONCMe2CMe2NO)](2+) (M4). The calculated geometrical parameters and oxidation potentials are in good agreement with the experimental data. As revealed by the DFT calculations, [Ru(II)(bpy)2(tmen)](2+) (M1) can undergo oxidative deprotonation to generate Ru-bis(imide) [Ru(bpy)2(tmen-4 H)](+) (A) or Ru-imide/amide [Ru(bpy)2(tmen-3 H)](2+) (A') intermediates. Both A and A' are prone to C-C bond cleavage, with low reaction barriers (ΔG(≠)) of 6.8 and 2.9 kcal mol(-1) for their doublet spin states (2)A and (2)A', respectively. The calculated reaction barrier for the nucleophilic attack of water molecules on (2)A' is relatively high (14.2 kcal mol(-1)). These calculation results are in agreement with the formation of the Ru(II)-bis(imine) complex M3 from the electrochemical oxidation of M1 in aqueous solution. The oxidation of M1 with Ce(IV) in aqueous solution to afford the Ru(II)-dinitrosoalkane complex M4 is proposed to proceed by attack of the cerium oxidant on the ruthenium imide intermediate. The findings of ESI-MS experiments are consistent with the generation of a ruthenium imide intermediate in the course of the oxidation.