Nickel-on-charcoal-catalyzed aromatic aminations and Kumada couplings: mechanistic and synthetic aspects.
Nickel-on-charcoal-catalyzed aromatic aminations and Kumada couplings: mechanistic and synthetic aspects.
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镍炭催化芳香胺化和 Kumada 偶联：机理和合成方面。
DOI：
10.1021/jo020297e
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发表时间：
2003
期刊：
影响因子：
--
通讯作者：
Lipshutz,BruceH
中科院分区：
文献类型：
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作者：
Tasler,Stefan;Lipshutz,BruceH
芳族胺化和Kumada偶联催化的“异质”镍炭（Ni/C）的协议已被修订，使它们更简单，更省时。对于这两种类型的反应，可以避免在添加底物之前使用n-BuLi还原催化剂前体Ni（II）/C。相反，在胺化反应中，发现胺与叔丁醇锂的组合将Ni（II）/C转化为活性Ni（0）。对于Kumada偶联，通过格氏试剂直接还原Ni（II）/C很容易实现。在不同的取代模式和具有不同的电子性质的三芳基膦配体的存在下运行的反应提供了深入了解这些镍催化转化的机制。无配体Kumada偶联容易与芳基Grignards反应，这可能是镍与试剂中芳基π-络合的结果。这两种类型的耦合的较大规模的反应已经成功地进行，这表明Ni/C基工艺可以按需放大。
Protocols for aromatic aminations and Kumada couplings catalyzed by ‘heterogeneous' nickel-on-charcoal (Ni/C) have been revised, making them simpler and more time efficient. For both types of reactions, reduction of the catalyst precursor Ni(II)/C usingn-BuLi prior to addition of a substrate can be avoided. Instead, in amination reactions, the amine in combination with lithiumtert-butoxide was found to convert Ni(II)/C to active Ni(0). For Kumada couplings, direct reduction of Ni(II)/C by the Grignard reagent is easily achieved. Reactions run in the presence of triarylphosphine ligands of varying substitution patterns and with differing electronic properties provided insight into the mechanism of these nickel-catalyzed transformations. Ligandless Kumada couplings were facile with aryl Grignards, which may be a consequence of π-complexation of nickel by the aryl group in the reagent. Larger scale reactions of both types of couplings have been successfully performed, suggesting that Ni/C-based processes can be scaled-up as needed.