Cationic arylpalladium complexes with chelating diamine ligands, [PdAr(N-N)(solv)]BF4 (N-N = N,N,N′,N′- tetramethylethylenediamine, 2,2′-bipyridine, 4,4′-dimethyl- 2,2′-bipyridine). Preparation, intermolecular coupling of the aryl ligands, and insertion of alkyne and allene into the Pd-C bond

Article abstract of DOI:10.1021/om0007466

Iodo(aryl)palladium complexes, [PdI{C₆H₃ (CF₃)₂-3,5}(N-N)] (N-N = tmeda, bpy, 4,4′-dimethyl-2,2′-bipyridine (Me₂bpy)), react with AgBF₄ in CH₃CN, acetone, and THF to yield stable cationic arylpalladium complexes [Pd{C₆H₃ (CF₃)₂-3,5}(N-N)(solv)]BF₄. A similar reaction of AgBF₄ with [PdI(C₆H₃Me₂-3,5) (bpy)] in CH₃CN gives [Pd(C₆H₃Me₂- 3,5)(bpy)(CH₃CN)]BF₄. The complex does not change its NMR spectrum for 1 h at room temperature in CD₃CN but undergoes decomposition upon dissolution in acetone to release 3,3′,5,5′- tetramethylbiphenyl. Addition of AgBF₄ to acetone or THF solutions of [PdI(Ar)(bpy)] (Ar = Ph, C₆H₃Me₂-3,5) and of [PdI(Ar)(Me₂bpy)] (Ar = C₆H₄OMe-4, C₆H₃Me₂-3,5) does not lead to isolation of the cationic arylpalladium complexes and causes intermolecular coupling of the aryl ligands to yield the corresponding biaryls. The reaction of AgBF₄ with [PdI(C₆H₃Me₂-3,5)(bpy)] in the presence of an excess amount of dimethyl acetylenedicarboxylate (DMAD) in CH₃CN gives [Pd(CZ=CZ-CZ=CZ-C₆H₃Me₂-3,5)(bpy) (CH₃CN)]BF₄ (Z = COOMe) via insertion of two acetylene molecules into the Pd-aryl bond. A similar reaction in acetone or THF causes insertion of three DMAD molecules into the Pd-aryl bond and cyclization of the formed Pd-(CZ=CZ)₃-Ar group to give the product containing a cyclopentadiene structure in the ligand. [PdI(CZ=CZ-C₆H₃ Me₂-3,5)(bpy)] reacts with AgBF₄ in CH₃CN to form a cationic complex, [Pd(CZ=CZ-C₆H₃Me₂-3,5) (bpy)(CH₃CN)]BF₄. A series of cationic Pd complexes, formed through insertion of one, two, and three alkyne molecules into the Pd-aryl bond, are characterized by X-ray crystallography or NMR spectroscopy. Phenylallene reacts with [PdI(C₆H₃Me₂-3,5) (bpy)] in the presence of AgBF₄ to give [Pd{η³-CH₂C-(C₆H₃ Me₂-3,5)CHPh}(bpy)]BF₄ via insertion of the C=C double bond of the allene into the Pd-C bond of the cationic arylpalladium complex. The π-allylpalladium complex crystallizes exclusively in a form with a syn-oriented phenyl substituent but exists in solution as a mixture of the isomers with a syn or anti phenyl substituent.