Ortho-metalated primary amines. 6. 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

When H2N(CH2)(2)C6H4OMe-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)(mu-OAc)(NH2R)](2) (2). When complex 2 is heated in acetonitrile at 80 degreesC, the ortho-metalated complex [Pd{C6H3(CH2)(2)NH2-2-OMe-5-kappa(2)C,N}(mu-OA)](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)(2)NH2-2-OMe-5-kappa(2)C,N}(mu-X)](2) (X = Cl (3b), Br (3c)). PPh3 splits the acetate or halide bridge in complex 3a or 3b to give [Pd{C6H3(CH2)(2)NH2-2-OMe-5-kappa(2)C,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)(2)NH2-2-X-5-kappa(2)C,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.