Immobilization of [Pd{(Ph2P)(2)N(CH2)(3)Si(OCH3)(3)-kappa P,P '}X-2] (X=Cl, Br) onto Montmorillonite: Investigating their Performance as Homogeneous or Heterogenized Suzuki-Miyaura Catalysts

Two palladium complexes, [Pd{(Ph2P)(2)N(CH2)(3)Si(OCH3)(3)-P,P'}X-2], X=Cl (2), Br (3), were synthesized and characterized by spectroscopic methods and X-ray crystallography. Complexes 2 and 3 contain a PdP2X2 square planar coordination sphere exhibiting small endocyclic P-Pd-P angles [71.49(4) and 71.53(5)degrees, respectively], the magnitude of which is controlled by the formation of the Pd-P-N-P four-membered chelating ring. Complexes 2 and 3 were found to be efficient catalysts in the Suzuki-Miyaura cross-coupling reaction of aryl bromides with phenylboronic acid at ambient or elevated temperature. At 100 degrees C, using 0.1mol% of palladium loading, high conversions were observed even after 15min. Both complexes were immobilized onto STx-1 montmorillonite clay via their -Si(OMe)(3) moiety, a process investigated by X-ray powder diffraction, X-ray fluorescence spectrometry, solid-state (PNMR)-P-31 spectroscopy and Scanning Electron Microscopy. The immobilized complexes, as heterogenized catalysts, displayed higher activity in the Suzuki-Miyaura coupling compared to that of the free complexes. The recyclability of the former was also explored.