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Nickel Complexes of a Pincer Amidobis(amine) Ligand: Synthesis, Structure, and Activity in Stoichiometric and Catalytic CC Bond‐Forming Reactions of Alkyl Halides
Author(s) -
Vechorkin Oleg,
Csok Zsolt,
Scopelliti Rosario,
Hu Xile
Publication year - 2009
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200802059
Subject(s) - chemistry , pincer ligand , alkyl , ligand (biochemistry) , medicinal chemistry , phosphine , reactivity (psychology) , pincer movement , amine gas treating , cationic polymerization , nickel , halide , coupling reaction , catalysis , metathesis , polymer chemistry , inorganic chemistry , organic chemistry , medicine , biochemistry , receptor , alternative medicine , pathology , polymer , polymerization
Get a grip! Ni II complexes of the new pincer amidobis(amine) ligand are described. The Ni chloride complex catalyzes Kumada–Corriu–Tamao coupling of unactivated alkyl halides with alkyl Grignard reagents, as well as double C–C coupling of CH 2 Cl 2 with alkyl Grignard reagents (see schemes).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 CC 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.