Ortho-Metalated Primary Amines. 6.1 The First Synthesis of Six-Membered Palladacycles from Primary Amines Containing Electron-Withdrawing Substituents: End of the Limiting Rules of Cope and Friedrich on Cyclopalladation of Benzyl- and Phenethylamines

Abstract

When H2N(CH2)2C6H4OMe-4 (RNH2) and Pd(OAc)2 are reacted in a 2:1 molar ratio, the complex [Pd(OAc)2(NH2R)2] (1) is obtained. Complex 1 reacts with 1 equiv of Pd(OAc)2 to give the dinuclear complex [Pd(OAc)(μ-OAc)(NH2R)]2 (2). When complex 2 is heated in acetonitrile at 80 °C, the ortho-metalated complex [Pd{C6H3(CH2)2NH2-2-OMe-5-κ2C,N}(μ-OAc)]2 (3a) is obtained. Complex 3a is also prepared by refluxing RNH2 and Pd(OAc)2 in a 1:1 molar ratio in acetonitrile. Complex 3a reacts with NaBr or LiCl to afford the complexes [Pd{C6H3(CH2)2NH2-2-OMe-5-κ2C,N}(μ-X)]2 (X = Cl (3b), Br (3c)). PPh3 splits the acetate or halide bridge in complex 3a or 3b to give [Pd{C6H3(CH2)2NH2-2-OMe-5-κ2C,N}X(PPh3)] (X = OAc (4a), Cl (4b)). With other 2-(phenyl)ethylamines or the corresponding chlorhydrates, Pd(OAc)2, and PPh3 as starting materials (molar ratio 1:1:1), the complexes [Pd{C6H3(CH2)2NH2-2-X-5-κ2C,N}Y(PPh3)] (Y = OAc, X = Cl (5), F (6); Y = Cl, X = NO2 (7)) have been isolated and fully characterized. These compounds include the first six-membered palladacycles synthesized from primary phenethylamines with electron-withdrawing substituents on the aryl ring. The crystal structures of 3a and 5 have been determined by X-ray diffraction.