The addition of O 2 on SPS-type pincer-based Rh(I) and Ir(I) complexes was studied by means of DFT calculations. The regioselectivity and the influence of the nature of the metal center on the reaction thermicity were related through a thermodynamic cycle to the electronic properties of the metal complex and to the energetics of the M−O bonds. The synthesis and the X-ray crystal structure analysis of the Ir(I) complex are also presented.