104130-32-7Relevant academic research and scientific papers
31P and 13C solid-state NMR of tertiary phosphine-palladium complexes bound to silica
Komoroski, Richard A.,Magistro, Angelo J.,Nicholas, Paul P.
, p. 3917 - 3925 (2008/10/08)
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 13C NMR is a good probe of ligand structure. The 36.44-MHz 31P spectrum of (≡SiOSiCH2CH2PPh2)2PdCl 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 31P chemical shifts of these compounds occur over a range of 127 ppm while the P-Pd-P angle varies from 73 to 91°. Hence, the 31P chemical shift is a very sensitive measure of strain in such complexes and confirms that the structures in solution are similar to those in the solid state. Applying these models, we find that the surface-bound complexes have mainly unstrained, trans configurations. Other species that have been examined on surfaces or as models include (dicyclohexylpropyl)phosphino complexes, for which cis and trans surface-bound complexes are observed, trimethylsilyl-capped samples, and phosphine oxides. Evidence is found for hydrogen bonding between bound phosphine oxide groups and silanol groups on the silica surface. Both the chemical shift anisotropy powder pattern and P-H cross-polarization rates indicate that the Pd-phosphine complex is rigidly bound to the silica surface.
