Palladium Complexes Containing Potentially Chelating Pyridylidene‐Type Carbene Ligands

Abstract

Abstract Oxidative addition of 2‐bromopyridine derivatives containing a potentially chelating donor group E (E = NMe 2 , SMe, SPh) to palladium(0) gives C , E ‐bound pyridylpalladium(II) complexes. Mono‐, di‐, and polymeric palladium complexes are obtained depending on the type of functionalization at the pyridyl nitrogen. With a lone pair at nitrogen, dimetallic products are isolated, while protonation gives monometallic pyridylidene‐type complexes. Remarkably, N ‐methylation inhibits chelating ligand coordination and a one‐dimensional polymer is formed instead. Heck‐type arylation of styrene is used as a probe for the catalytic activity of the palladium pyridylidene complexes and reveals moderate activities. Mechanistic studies support a heterogeneous mode of action, including loss of the pyridylidene‐type ligand from the metal coordination sphere.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)