Stamatopoulos, Ioannis, Roulia, Maria, Vallianatou, Kalliopi A., Raptopoulou, Catherine P., Psycharis, Vassilis, Carravetta, Marina, Papachristodoulou, Christina, Hey-Hawkins, Evamarie, Kostas, Ioannis D. and Kyritsis, Panayotis (2017) Immobilization of [Pd{(Ph2P)2N(CH2)3Si(OCH3)3-κP,P'}X2] (X=Cl, Br) onto Montmorillonite: Investigating their Performance as Homogeneous or Heterogenized Suzuki-Miyaura Catalysts. ChemistrySelect, 2 (36), 12051-12059. (doi:10.1002/slct.201702601).
Abstract
Two palladium complexes, [Pd{(Ph2P)2N(CH2)3Si(OCH3)3-κP,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)°, 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 °C, 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 31P NMR 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.
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