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

Abstract

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.

Intramolecular Nitrene Insertion into Saturated C−H‐Bond‐Mediated C−N Bond Cleavage of a Coordinated NHC Ligand

“…The computed Ru=NTsb ond length of RC is 1.868 and 1.892 in the singlet and triplet states, respectively,f alling in the range of the calculated Ru=NR distances (1.83-1.97 ) reportedi nt he literature. [15] The first step reaction is the intramolecular nitreneC ÀHi nsertion, withabarrier of only 6.5 kcal mol À1 for the singlet state and 13.1 kcal mol À1 for the triplet state, andt he spin crossing occurs before the transition state hence leading to ab arrier of 11 kcal mol À1 .F ormation of the singlet intermediate 1 INT (B)i sh ighly exergonicw ith af ree energy change of À38.4 kcal mol À1 . 1 INT can undergo ano xidative deprotonation process to form 1 INT-H (3-H Ts )w ith af ree energy penalty of only 4.4 kcal mol À1 .T he cleavage of the CÀN bond and the formation of the C=Nb ond happeni nstantaneously in the subsequent rearrangement reaction to give 1 PR-H.…”