IRON COMPLEX-CATALYZED CROSS COUPLING OF HALIDE COMPOUNDS AND ORGANOMAGNESIUM REAGENTS

Abstract

The effect of reaction conditions in the iron-catalyzed cross-coupling of alkyl halide and arylmagnesium reagents was studied. It was found that a solvent system was the main factor that affected the yield of cross-coupling. Using toluene as a solvent gave higher yield of cross-coupling product than other solvents. The previously reported requirements such as slow addition rate of the reagent, excessive additive, and special ligand could be omitted, while providing high product yield. Under the optimized condition, employing FeCl3 as a very simple iron catalyst gave the yield of cross-coupling product up to 92% for bromocyclohexane substrate and 76% for chlorocyclohexane. In the ligand effect study, the 1,3-dicarbonyl ligand with electron-donating substituent provided the highest %conversion of chlorocyclohexane substrate. In the case of bromocyclohexane, the conversion was complete in all cases of different ligands. However, the ligand with electron-withdrawing group minimized the amount of by-products obtained. Utilizing iron precatalysts combination, containing Fe(dbm-derivative)3 and FeCl3, showed the best result. The appropriate catalyst loading was 2.5 mol% of Fe(dbm-derivative)3 and 2.5 mol% of FeCl3. This method gave 94% cross-coupling product yield from bromocyclohexane and 85% from chlorocyclohexane. Other substrates were also employed, the results showed that increasing steric hindrance of substrates could obstruct the reaction.