| 19229933 |
Vechorkin O, Csok Z, Scopelliti R, Hu X: Nickel complexes of a pincer amidobis (amine) ligand: synthesis, structure, and activity in stoichiometric and catalytic C-C bond-forming reactions of alkyl halides. Chemistry. 2009;15(15):3889-99.
The synthesis, properties, and reactivity of nickel (II) complexes of a newly developed pincer amidobis (amine) ligand ((Me) NN (2)) are described. Neutral or cationic complexes [((Me) NN (2)) NiX] (X = OTf (6), OC (O) CH (3) (7), CH (3) CN (8), OMe (9)) were prepared by salt metathesis or chloride abstraction from the previously reported [((Me) NN (2)) NiCl] (1). The Lewis acidity of the {((Me) NN (2)) Ni} fragment was measured by the (1) H NMR chemical shift of the coordinated CH (3) CN molecule in 8. Electrochemical measurements on 1 and 8 indicate that the electron-donating properties of NN (2) are similar to those of the analogous amidobis (phosphine) (pnp) ligands. The solid-state structures of 6-8 were determined and compared to those of 1 and [((Me) NN (2)) NiEt] (3). In all complexes, the (Me) NN (2) ligand coordinates to the Ni (II) ion in a mer fashion, and the square-planar coordination sphere of the metal is completed by an additional donor. The coordination chemistry of (Me) NN (2) thus resembles that of other three-dentate pincer ligands, for example, pnp and arylbis (amine) (ncn). Reactions of 2 with alkyl monohalides, dichlorides, and trichlorides were investigated. Selective C-C bond formation was observed in many cases. Based on these reactions, efficient Kumada-Corriu-Tamao coupling of unactivated alkyl halides and alkyl Grignard reagents with 1 as the precatalyst was developed. Good yields were obtained for the coupling of primary and secondary iodides and bromides. Double C-C coupling of CH (2) Cl (2) with alkyl Grignard reagents by 1 was also realized. The scope and limitations of these transformations were studied. Evidence was found for a radical pathway in Ni-catalyzed C-C cross-coupling reactions, which involves Ni (II) alkyl intermediates. |
1(0,0,0,1) |