Immobilization of Bisphosphinoamine Linkers on Silica: Identification of Previously Unrecognized Byproducts via ³¹P CP/MAS and Suspension HR-MAS Studies

A new bisphosphinoamine linker with ethoxysilyl group has been synthesized and applied for anchoring nickel catalysts to alumina and silica. Side reactions occurred, and the reactions of various bisphosphinoamine ligands with silica were studied by 31 P CP/MAS and suspension HR-MAS NMR. Besides the desired immobilization, two main side reactions have been found. The phosphine moieties of the linkers can be quaternized by ethyl groups from the ethoxysilyl functions. Furthermore, the bisphosphinoamine group can rearrange to the corresponding phosphinimine unit that is subsequently hydrolyzed, resulting in the amine and tetraphenyldiphosphine oxide. The latter is bound firmly to the silica surface.