Phosphaalkenes palladium(II) complexes in the Suzuki and Sonogashira cross-coupling reactions

The 1-methoxy-2-(supermesitylphosphanylidenemethyl)-benzene ligand (1) was prepared by reacting the phospha-Wittig reagent [Mes*P=PMe3] with o-methoxybenzaldehyde. Reaction of I with one equivalent of the [Pd(allyl)Cl](2) dimer in the presence of Ag(OTf) affords a neutral complex (4) in which the triflate ligand is coordinated to the palladium atom. DFT calculations show that the formation of complex 4 is favored by 22.4 kcal/mol with respect to that of a chelate species involving coordination of the ligand through the phosphorus atom of one lone pair at the oxygen of the pendant methoxy group. Reaction of two equivalents of ligand I with the [Pd(allyl)Cl](2) dimer affords complex 5, in which the two ligands are coordinated through their phosphorus atom. The catalytic activity of complex 5 was compared to that of the 1, 3-bis[2-(super-mesityl)phosphanediylmethyl]benzene palladium chloride complex (6). Performances of the two catalysts were found to be similar in the Suzuki cross-coupling reaction between phenylboronic acid and some arylbromides (TON between 55.10(5) and 99.10(5)) as well as in the Sonogashira coupling between phenylacetylene and arylbromides (TON between 400 and 950). (c) 2007 Wiley Periodicals, Inc.