An X-ray Photoelectron Spectroscopy Study of Variations in the Stability of [M(COD)Cl]₂ (M = Ir, Rh) Complexes Anchored on Modified Silica in the Spin-Selective Hydrogenation of Unsaturated Hydrocarbons with Parahydrogen

Changes in the composition of immobilized [M(COD)Cl]₂–NH₂–C₃H₆–SiO₂ and [M(COD)Cl]₂–P(Ph)₂–C₂H₄–SiO₂ (where M = Ir, Rh) catalysts in the gas-phase selective hydrogenation of propylene, propyne, and 1,3-butadiene with parahydrogen (p-H₂) have been studied by the XPS method. It has been proposed that the M/Cl atomic ratio should be used as an indicator of the structural stability of the anchored complex both at the sample synthesis stage and in the reaction. Based on comparison of XPS data and results of catalytic tests using parahydrogen-induced nuclear polarization, it has been shown that the stability of the anchored {[M(COD)Cl]₂–Linker–SiO₂} complex during hydrogen activation is a key factor in the catalytic behavior of the systems. The stability of the complex is affected not only by the chosen metal and linker, but also by the nature of the substrate subjected to hydrogenation.