Immobilization of carbonylnickel complexes: A solid-state NMR study

Silica is commonly modified with bifunctional phosphines like PPh(2)CH(2)CH(2)Si(OEt)(3) prior to immobilization of catalysts. Here, besides PPh(2)(CH2)(3)Si(OEt)(3), ligands that are more stable toward oxidation, namely PPh(2)(C6H4)Si(OEt)(3), PPh(2)(C6H4)SiMe(2)(OEt), and PPh(2)(CH2)(4)OH, are applied. The di- and tricarbonylnickel complexes of these ligands are synthesized, characterized by Ni-61, (31)p, C-13, and H-1 NMR and IR spectroscopy, and immobilized on silica. Alternatively, the corresponding phosphine-modified silicas are treated with Ni(CO)(4). The obtained materials are investigated by P-31 and C-13 solid-state NMR spectroscopy. Di- and tricarbonylnickel species can be distinguished by their different chemical shift anisotropies and also by their IR data. While the first route allows immobilization of both di- and tricarbonylnickel complexes, reaction of surface-bound phosphines with Ni(CO)(4) gives the tricarbonyl species exclusively. Among the different ligands, PPh(2)(CH2)(4)OH has optimal qualities: It gives high surface coverages without oxidation or cross-linking, and therefore narrow NMR lines, and it allows C-13 CP/MAS NMR spectroscopy.