Coupling reactions Grignard reagents/cobalt salts

A series of papers have also reported the coupling of alkyl and aryl electrophiles with aryl Grignard reagents catalyzed by iron (Equation 19.15) and cobalt complexes. These reactions build upon Kochi s and Molander s early results on coupling reactions catalyzed by complexes of these metals. The recent reactions have been conducted with simple metal salts in many cases and with discrete metal complexes as catalyst precursors in others. Although little recent mechanistic data is available on these reactions, they have earlier been shown to involve radical intermediates. Kochi concluded that the catalytic process occurs by an Fe(I)-Fe(III) couple reactions of optically active alkyl halides generate racemic coupled products and reactions of diastereomerically pure aUcyl halides generate equal ratios of diastereomeric products, as depicted in Equations 19.16 and 19.17. ... 

---