A Kumada Coupling Catalyst, [Ni{(Ph2P)2N(CH2)3Si(OCH3)3-P,P}Cl2], Bearing a Ligand for Direct Immobilization Onto Siliceous Mesoporous Molecular Sieves
Abstract
The ligand-exchange reaction between [Ni(PPh3)(2)Cl-2] and (Ph2P)(2)N(CH2)(3)Si(OCH3)(3) afforded the novel Ni-II complex [Ni{(Ph2P)(2)N(CH2)(3)Si(OCH3)(3)-P,P}Cl-2] (1) in which the square-planar NiP2Cl2 coordination sphere contains a four-membered Ni-P-N-P ring. Comparison of the structure of 1 and related Ni-II square-planar or Ni-0 tetrahedral complexes containing similar P-N-P ligands shows that the magnitude of the P-Ni-P angle is controlled by the presence of the Ni-P-N-P ring, irrespective of the geometry of the nickel coordination sphere.
Direct anchoring of 1 onto SBA-15 molecular sieves through the trimethoxysilyl end-group of the ligand afforded heterogeneous catalyst 1/SBA-15. Both 1 and 1/SBA-15 catalyze Kumada cross-coupling reactions, exhibiting similar activity and a slightly higher product selectivity than the [Ni{Ph2P(CH2)(3)PPh2-P,P}Cl-2] and [Ni{(Ph2P)(2)N-(S)-CHMePh-P,P}X-2] (X = Cl, Br) complexes described in the literature.
The Grignard reagent employed is likely to induce leaching of the catalyst, which retains its activity in solution.