XPS study of the stability variations of [M(COD)Cl]<SUB>2</SUB> (M = Ir, Rh) complexes anchored on modified silica in reactions of spin-selective hydrogenation of unsaturated hydrocarbons by parahydrogen

Changes in the composition of anchored [M(COD)Cl]2–NH2–C3H6–SiO2 and [M(COD)Cl]2–P(Ph)2–C2H4–SiO2 (where M = Ir, Rh) catalysts in reactions of gas-phase selective hydrogenation of propene, propyne and 1,3-butadiene with parahydrogen (p-H2) were studied using XPS. The atomic ratio M/Cl has been proposed as an indicator of the stability of the structure of the anchored complex, both at the stage of sample preparation and in the reaction. Based on a comparison of XPS data and the results of catalytic testing using parahydrogen-induced polarization, it is 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 systems. Such stability is influenced not only by the chosen metal and linker, but also by the nature of the hydrogenated substrate.