New transformations of unsaturated hydrocarbon ligands coordinated with mono- and dinuclear palladium units

Some insights into mechanistic features of M-C bond formation (oxidative addition) and bond cleavage (reductive elimination) about allyl-palladium complexes are presented based on new transformations of allylic as well as propargylic ligands bound to Pd and Pt. 1) The oxidative addition is proposed to proceed through initial pi-complex formation between allylic electrophiles and M(0) atom, which is followed by intramolecular eta(3)-allyl-M bond formation with either inversion or retention of configuration at an allylic sp(3)-carbon depending on the nature of ligands and solvents. 2) The reductive elimination of allyl(organo)palladium complexes is suggested to proceed via cis C-C coupling between eta(3)-allyl and eta(1)-bound organic ligands. 3) A Pd(0) nucleophile is shown to exhibit dual selectivity with regard to the site of its attack on allylpalladium complexes depending on the nature of their ligands, leading to either redox transmetallation with net inversion of configuration at the allylic sp(3)-carbon, or mu-allyl Pd-Pd complex formation with retention of stereochemistry. Some novel bonding and reactivity trends in those Pd-Pd bonded complexes which contain mu-allyl, mu-propargyl and mu-diene ligands are also presented.