Phosphine ligands have been demonstrated to have an effect on reactivity and selectivity in the competitive intramolecular palladium-catalysed Suzuki-Miyaura coupling of dibromo sulfoxide 1a possessing two different hybridised electrophilic carbons. It was found that the bromine bond to the sp3-hybridised carbon is selectively replaced in the presence of unhindered phosphines such as PPh3 or xantphos. The use of hindered phosphine ligands such as P(o-tol)3 and P(1-naphthyl)3 reversed the selectivity, conducting the cross-coupling at the Csp 2-Br. Identical trends were observed in external competition experiments carried out with bromomethyl sulfoxide and different substituted bromoarenes. DFT and DFT/MM calculations showed that the selectivity observed is mainly due to the different facility of the ligands to dissociate. Bisphosphine catalysts favour coupling at the sp3 carbon, whereas monophosphine catalysts prefer the sp2 carbon. Customised catalysts: Proper selection of the phosphine ligand in the palladium catalyst enables a highly intra- and intermolecular selective Suzuki-Miyaura coupling at either Csp 3-Br or Csp2-Br (see figure). DFT and DFT/MM calculations show that the selectivity observed is mainly due to the different facilities of the ligands for dissociation. Copyright © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
|Journal||Chemistry - A European Journal|
|Publication status||Published - 3 Dec 2010|
- density functional calculations
- ligand effects
- reaction mechanisms