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

Abstract

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.

Ligand‐Controlled Palladium(II)‐Catalyzed Regiodivergent Carbonylation of Alkynes: Syntheses of Indolo[3,2‐c]coumarins and Benzofuro[3,2‐c]quinolinones

“…After coordination with L5,t he palladium center becomes more electrophilic,t hus coordinating the amino group and simultaneously activating the alkyne to form the intermediate A rather than A' '.T hen the intermediate B is generated by the nucleophilic cyclization. Thes ubsequent CO insertion [13] delivers the complex C. [14,15] Reductive elimination affords the benzofuro[3,2-c]-…”

Detection of Palladium(I) in Aerobic Oxidation Catalysis

“…These results may be compared to the involvement of Pd I species in carbonylation [18] and cross-coupling reactions. [19,20] For example, dimeric Pd I complexes have been used as pre-catalysts or observed as intermediates in diverse cross-coupling reactions.…”

Ligand‐Controlled Palladium(II)‐Catalyzed Regiodivergent Carbonylation of Alkynes: Syntheses of Indolo[3,2‐c]coumarins and Benzofuro[3,2‐c]quinolinones

“…Then the intermediate B is generated by the nucleophilic cyclization. The subsequent CO insertion delivers the complex C . Reductive elimination affords the benzofuro[3,2‐ c ]quinolinones 2 and Pd 0 species, which is oxidized to Pd II by BQ .…”