Immobilization of [Pd{(Ph2P)2N(CH2)3Si(OCH3)3-kP,P’}X2] (X=Cl, Br) onto Montmorillonite: Investigating their Performance as Homogeneous or Heterogenized Suzuki-Miyaura Catalysts

摘要

Two palladium complexes, [Pd{(Ph2P)2N(CH2)3Si(OCH3)3-kP,P’}X2], 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)8, 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 8C, using 0.1 mol% of palladium loading, high conversions were observed even after 15 min. 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 31PNMR 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.