Synthesis, Characterization, and Reactivity of Arylpalladium Cyanoalkyl Complexes:  Selection of Catalysts for the α-Arylation of Nitriles

• Published in: Journal of the American Chemical Society 2002-08, Vol.124 (32), p.9330-9331
• Main Authors: Culkin, Darcy A, Hartwig, John F
• Format: Article
• Language: English
• Subjects: Catalysis; Catalysts: preparations and properties; Chemistry; Exact sciences and technology; General and physical chemistry; Magnetic Resonance Spectroscopy; Models, Molecular; Nitriles - chemistry; Palladium - chemistry; Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/ja026584h

A new coupling process, the palladium-catalyzed α-arylation of nitriles, was developed by exploring the structure and reactivity of arylpalladium cyanoalkyl complexes. Complexes of 1,2-bis(diphenylphosphino)benzene (DPPBz), 1,1‘-bis(di-i-propylphosphino)ferrocene (D i PrPF), racemic-2,2‘-bis(diphenylphosphino)-1,1‘-binaphthyl (BINAP), and diphenylethylphosphine (PPh2Et) were prepared. Coordination to palladium through the α-carbon was observed for DPPBz-ligated complexes and for complexes of primary and benzylic nitrile anions. However, the anion of isobutyronitrile was coordinated to palladium through the cyano-nitrogen when the complex was ligated by D i PrPF. The isobutyronitrile anion displaced a phosphine ligand to form a C,N-bridged dimer when generated from PPh2Et-ligated palladium. These results suggest that the nitrile anion preferentially coordinates to palladium through the carbon atom in the absence of steric effects. Thermolysis of the arylpalladium cyanoalkyl complexes led to reductive elimination that formed α-aryl nitriles. The high yields and short reaction times observed for BINAP-ligated complexes suggested that BINAP-ligated palladium catalysts might be appropriate for the arylation of nitriles. Initial results on a palladium-catalyzed process for the direct coupling of aryl bromides and primary, benzylic, and secondary nitrile anions to form α-aryl nitriles in good yields are reported.