C(sp3),N palladacyclic complexes bearing flexidentate ligands as efficient (pre)catalysts for Heck olefination of aryl halides

Abstract C,N-cyclopalladated complexes are among the most robust and widely used (pre)catalysts of cross-coupling reactions, combining long shelf life with high catalytic activity. In this report, we describe synthesis and properties of new Pd(II) complexes of a flexidentate ligand – 2,2-dimethyl-5-(2-pyridyl)pentane-3,5-dione (HL). Its coordinating properties resulted in the formation of two stereoisomeric cis- and trans-PdL2 complexes each with one ligand in O,O- and the other in N,C(sp3)-coordination modes. The solid-state structures have been established by means of single-crystal X-ray diffraction methods and are retained in solution as indicated by NMR spectroscopy. Both these isomers proved to be efficient (pre)catalysts of phosphine-free Heck cross-coupling of iodoarenes with olefins.