School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, Georgia 30332-0400, USA.
J Am Chem Soc. 2010 Oct 20;132(41):14358-60. doi: 10.1021/ja106212w.
Square planar cobalt(III) complexes with redox-active amidophenolate ligands are strong nucleophiles that react with alkyl halides, including CH(2)Cl(2), under gentle conditions to generate stable square pyramidal alkylcobalt(III) complexes. The net electrophilic addition reactions formally require 2e(-) oxidation of the metal fragment, but there is no change in metal oxidation state because the reaction proceeds with 1e(-) oxidation of each amidophenolate ligand. Although the four-coordinate complexes are very strong nucleophiles, they are mild outer-sphere reductants. Accordingly, addition of alkyl- or phenylzinc halides to the five-coordinate organometallic complexes regenerates the square planar starting materials and extrudes C-C coupling products. The net 2e(-) reductive elimination reaction also occurs without a oxidation state change at the cobalt(III) center. Together these reactions comprise a complete, well-defined cycle for cobalt Negishi-like cross-coupling of alkyl halides with organozinc reagents.
具有氧化还原活性的酰胺苯酚配体的平面正方形钴(III)配合物是强亲核试剂，可在温和条件下与烷基卤化物（包括 CH(2)Cl(2)）反应，生成稳定的平面四方烷基钴(III)配合物。这些亲核加成反应的净结果需要金属片段发生 2e(-)氧化，但由于每个酰胺苯酚配体发生 1e(-)氧化，金属氧化态没有变化。尽管四配位配合物是很强的亲核试剂，但它们是温和的外球还原剂。因此，向五配位有机金属配合物中添加烷基或芳基锌卤化物，可将反应再生为平面正方形起始原料并挤出 C-C 偶联产物。净 2e(-)还原消除反应也在钴(III)中心不发生氧化态变化的情况下发生。这些反应共同构成了一个完整的、明确的循环，用于钴 Negishi 型交叉偶联烷基卤化物与有机锌试剂。
