A soluble polyethyleneglycol-anchored phosphine as a highly active, reusable ligand for Pd-catalyzed couplings of aryl chlorides:: comparison with cross and non-cross-linked polystyrene and silica supports

The so-called SPhos phosphine, an extremely active ligand in the amination and Suzuki coupling of sterically-hindered aryl chlorides, has been anchored on different supports such as non-soluble (cross-linked polystyrene) and soluble (non-cross-linked polystyrene and polyethyleneglycol) polymers, as well as high surface silica. SPhos anchored on polyethyleneglycol (PEG-SPhos) showed the best activity for both amination and Suzuki couplings. The PEG-SPhos ligand can be quantitatively recovered from the reaction mixture through precipitation with diethyl ether and recycled in four consecutive runs without loosing activity. P-31 NMR spectra of the reused anchored ligand showed that deactivation of the PEG-SPhos ligand comes from the progressive oxidation of the phosphine-to-phosphine oxide. (C) 2007 Elsevier Ltd. All rights reserved.