Phosphorus-31 and carbon-13 solid-state NMR of tertiary phosphine-palladium complexes bound to silica

Abstract

Phosphorus-31 and carbon-13 NMR spectra with cross polarization and magic-angle spinning are used to characterize palladium-tertiary phosphine complexes and their precursors covalently bound to silica. Phosphorus-31 NMR is a good probe of complex formation and geometry, whereas /sup 13/C NMR is a good probe of ligand structure. The 36.44-MHz /sup 31/P spectrum of (identical with SiOSiCH/sub 2/CH/sub 2/PPh/sub 2/)/sub 2/PdCl/sub 2/ shows two, barely resolved peaks at about 21 and 30 ppm assigned to the trans and cis complexes, respectively. These assignments are based on the chemical shifts of model compounds in both solution and the solid state. Uncomplexed phosphine and phosphine oxide are observed when complexes are prepared from phosphinated silica but not when the complexes are preformed and then attached to silica. The palladium dichloride complexes of bis(diphenylphosphino)methane, -ethane, and -propane, all of which have an approximately square-planar configuration, were examined as solid-state models for strained cis complexes on the silica surface. As in solution, the solid-state /sup 31/P chemical shifts of these compounds occur over a range of 127 ppm while the P-Pd-P angle varies from 73 to 91/sup 0/. Hence, the /sup 31/P chemical shift is a very sensitive measure of strain in such complexes andmore » confirms that the structures in solution are similar to those in the solid state.« less