Phosphaalkenes palladium(II) complexes in the suzuki and sonogashira cross-coupling reactions†
For further details on the theoretical structure of complexes I and II and the X-ray structural data for complexes 4 and 5, contact Pascal Le Floch.
Abstract
The 1-methoxy-2-(supermesitylphosphanylidenemethyl)-benzene ligand (1) was prepared by reacting the phospha-Wittig reagent [Mes*PPMe3] with o-methoxybenzaldehyde. Reaction of 1 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 1 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-(supermesityl)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 55.105 and 99.105) as well as in the Sonogashira coupling between phenylacetylene and arylbromides (TON between 400 and 950). © 2007 Wiley Periodicals, Inc. Heteroatom Chem 18:363–371, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.20307