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

Abstract

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(CZCZ−CZCZ−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−(CZCZ)3−Ar group to give the product containing a cyclopentadiene structure in the ligand. [PdI(CZCZ−C6H3Me2-3,5)(bpy)] reacts with AgBF4 in CH3CN to form a cationic complex, [Pd(CZCZ−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(C6H3Me2-3,5)CHPh}(bpy)]BF4 via insertion of the CC 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.