Mapping Palladium Reduction by Carbon Monoxide in a Catalytically Relevant System. A Novel Palladium(I) Dimer

Reaction of neutral palladium(II) complexes with chelating nitrogen ligands of the phenanthroline family had been earlier found to proceed through the formation of a CO adduct, which is then reduced to another observable complex before decomposing to metallic palladium. We have now extended this study and completely characterized by single-crystal X-ray diffraction one member of this class of compounds. The intermediate is an unprecedented type of palladium(I) dimer with two bridging COs. The same complex could also be obtained by a conproportionation reaction of a Pd0 with a PdII complex. The picture of the reactivity of neutral palladium(II) complexes with phenanthroline ligands in a CO atmosphere was completed by the identification of two byproducts of the main reaction.