Mechanistic insights into the chemistry of Ru(II) complexes containing Cl and DMSO ligands

Two new isomers trans,mer-[(RuCl2)-Cl-II(bpea)(DMSO)], 2a, and cis,fac-[(RuCl2)-Cl-II(bpea)(DMSO)], 2b, (bpea = N,N-bis-(2-pyridylmethyl)ethylamine), as well as the bis-DMSO complex trans, fac-[(RuCl)-Cl-II(bpea) (DMSO)(2)]Cl, 3, have been synthesized and characterized by cyclic voltammetry and UV-vis and 1D and 2D NMR spectroscopy in solution. Their solid-state structure has also been solved by means of single-crystal X-ray diffraction analysis. All the three complexes display a ruthenium metal center possessing a distorted-octahedral type of coordination, where the bpea ligand is coordinated in a meridional fashion in 2a and in a facial fashion in 2b and 3. The isomer 2a is the kinetically favored and thus can be thermally converted into 2b, that is the thermodynamically favored one. A thorough kinetic analysis strongly points toward a dissociative mechanism, where in the first step a chloro ligand is removed from the metal coordination sphere, followed by a geometric rearrangement before the chloro, ligand coordinates again, generating the final complex. DFT calculations agree with the experimental data for the proposed mechanism and allow us to further characterize the mechanism of the 2a -> 2b rearrangement by obtaining the intermediates and transition state.