Stereoselective hydrodehalogenation via a radical-based mechanism involving T-shaped chiral nickel(I) pincer complexes.
Stereoselective hydrodehalogenation via a radical-based mechanism involving T-shaped chiral nickel(I) pincer complexes.
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DOI：
10.1002/chem.201403243
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发表时间：
2014-07
期刊：
影响因子：
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通讯作者：
Christoph A. Rettenmeier;H. Wadepohl;L. Gade
中科院分区：
文献类型：
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作者：
Christoph A. Rettenmeier;H. Wadepohl;L. Gade
本文报道了基于手性分子镍(I)/镍(II)氢化物体系相互作用的催化对映体选择性加氢脱卤化反应。前手性双卤化物通过二次构型不稳定，可能是金属稳定的自由基中间体进行脱卤化。在接下来的步骤中，被释放的自由基被镍(II)氢化物捕获，在催化条件下，镍(II)氢化物以大量过剩存在，这反过来又在氢原子转移到自由基中间体的过程中诱导了对映体选择性。这些新的手性镍(I)配合物以LiEt3-BH为还原剂，催化了具有中等到良好对映体过量值的双卤化物的不对称加氢脱卤化反应。通常观察到的主要副产物是脱卤烯，而手性单卤化物的加氢脱卤化反应要慢得多，尽管还原剂大量过剩。
We herein report the catalytic enantioselective hydrodehalogenation based on the interplay of a chiral molecular nickel(I)/nickel(II)hydride system. Prochiral geminal dihalogenides are dehalogenated via a secondary configurationally unstable, potentially metal-stabilized radical intermediate. In a subsequent step, the liberated radical is then trapped by the nickel(II) hydrido complex, present in a large excess under the catalytic conditions, which in turn induces the enantioselectivity during the hydrogen atom transfer onto the radical intermediate. These new chiral nickel(I) complexes were found to catalyze the asymmetric hydrodehalogenation of geminal dihalogenides with moderate to good enantiomeric excess values using LiEt3 BH as reductant. The main side product generally observed is the dehalogenated alkene, whereas the hydrodehalogenation of the chiral monohalogen compound occurred much more slowly despite the large excess of reductant.