共 65 条
Mechanistic Characterization of (Xantphos)Ni(I)-Mediated Alkyl Bromide Activation: Oxidative Addition, Electron Transfer, or Halogen-Atom Abstraction
被引:131
作者:
Diccianni, Justin B.
[1
]
Katigbak, Joseph
[1
]
Hu, Chunhua
[1
]
Diao, Tianning
[1
]
机构:
[1] NYU, Dept Chem, 100 Washington Sq East, New York, NY 10003 USA
基金:
美国国家科学基金会;
关键词:
CROSS-COUPLING REACTIONS;
SUBSTITUTION-REACTIONS;
BIARYL SYNTHESIS;
ORGANIC HALIDES;
ARYL HALIDES;
NICKEL;
NI(I);
COMPLEXES;
CATALYSIS;
NI;
D O I:
10.1021/jacs.8b13499
中图分类号:
O6 [化学];
学科分类号:
0703 ;
摘要:
Ni(I)-mediated single-electron oxidative activation of alkyl halides has been extensively proposed as a key step in Ni-catalyzed cross-coupling reactions to generate radical intermediates. There are four mechanisms through which this step could take place: oxidative addition, outer-sphere electron transfer, inner-sphere electron transfer, and concerted halogen atom abstraction. Despite considerable computational studies, there is no experimental study to evaluate all four pathways for Ni(I)-mediated alkyl radical formation. Herein, we report the isolation of a series of (Xantphos)Ni(I)-Ar complexes that selectively activate alkyl halides over aryl halides to eject radicals and form Ni(II) complexes. This observation allows the application of kinetic studies on the steric, electronic, and solvent effects, in combination with DFT calculations, to systematically assess the four possible pathways. Our data reveal that (Xantphos)Ni(I)-mediated alkyl halide activation proceeds via a concerted halogen-atom abstraction mechanism. This result corroborates previous DFT studies on (terpy)Ni(I)- and (py)Ni(I)-mediated alkyl radical formation, and contrasts with the outer-sphere electron transfer pathway observed for (PPh3)(4)Ni(O)-mediated aryl halide activation. This study of a model system provides insight into the overall mechanism of Ni-catalyzed cross-coupling reactions and offers a basis for differentiating electrophiles in cross-electrophile coupling reactions.
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页码:1788 / 1796
页数:9
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