XPS Study of the [Ir(COD)Cl]2–L–SiO2 Catalytic System

Abstract

The X-ray photoelectron spectroscopy (XPS) and nuclear magnetic resonance (NMR) spectroscopy were used to study the features of anchoring of the [Ir₂(COD)₂Cl₂] complex on the surface of modified silica gel L–SiO₂ (where L is NC₅H₅–CH₂–CH₂–, N(CH₃)₂–CH₂–CH₂–CH₂–, NH₂–C₃H₆–) depending on the nature of the linker and the conditions of preparation of the systems. The catalytic activity was tested in reactions of gas-phase selective hydrogenation of propylene with parahydrogen (p-H₂). According to the XPS data, a single-site iridium catalyst is prepared in all cases. Analysis of the XPS spectra indicates the possibility of anchoring the complex through one of the iridium atoms while preserving the dimer. It was shown that at different durations of interaction of the iridium complex solution with modified NH₂–C₃H₆–silica gel approximately the same amount of the complex is anchored, but the nature of the complex coordination changes. For the sample obtained by long-term interaction of the complex solution with the modified support (24 h), a high increase in the NMR signal was observed at 60°C, while in the case of the sample prepared by short-term interaction (1 h), the signal increased with a rise in temperature to 80°C.