Catalytic cross coupling reactions

Dahadha, Adnan GND

Transistion metal catalyzed cross coupling reactions are among the most versatile methods for establishing new carbon-carbon bonds. Nevertheless, (Csp3-Csp2) coupling features several synthetic problems i.e. the correct choice of the nature of electrophile and nucleophile or the appearance of homocoupling products. In this work Kumada type cross coupling reactions of alkyl Grignard reagents with different types of aromatic electrophiles were investigated. Transition metal compounds of the general formula {MCl2[Ph2P(CH2)1-3PPh2]} (M = Pd, Ni, Fe) are versatile precatalysts for the coupling of cyclohexyl Grignard reagents with either fluorinated bromobenzene or bromothiophene derivatives, catalytic activity of the precatalysts depends on the diphosphane ligands and increases in the order dppm < dppe < dppp, if cyclohexyl Grignard solutions without any additives are used, the catalytic activity of the precatalysts depends on the transition metal and increases in the order Fe < Ni < Pd. The addition of lithium salts to the Grignard solutions leads to an enhancement of activity for all precatalysts. The effect is most pronounced for iron precatalysts which upon addition of LiBr show an activity that is well comparable to that of palladium complexes under the same reaction conditions.




Dahadha, Adnan: Catalytic cross coupling reactions. 2012.


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