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Reactivity and Dynamics of Bifunctional Phosphines Immobilized on Oxidic Supports – A Solid‐State NMR Study

The successful immobilization of transition metal catalysts on oxidic surfaces via bifunctional phosphines like PPh 2 (CH 2 ) 3 Si(OEt) 3 is crucially dependent upon the knowledge of the reactions of both their functionalities with the surface. In this study, solid-state NMR spectroscopy served as a powerful analytical tool. The nature of a P(V) byproduct, generated by the combined action of ethoxysilane groups and silica surface, has been investigated and ways have been shown to avoid it. The study of the reactions of ethoxysilanes with silica surfaces led to the discovery, that addition reactions with surface siloxane groups play a dominant role. Therefore, the surface coverage can be optimized and later leaching of the catalyst prevented by using rigorously dried silica. The success of the developed concepts was demonstrated by the selective immobilization of di- and tricarbonyl-nickel complexes. Both types of complexes can be distinguished by their characteristic 31 P solid-state NMR spectra. The dynamics of immobilized phosphines and carbonylnickel complexes in the presence of different solvents has been studied by 31 P suspension NMR spectroscopy. Polar, non-viscous solvents gave the narrowest resonances, corresponding to the greatest mobility of the surface-bound species.