Carbon-halide bond activation Suzuki reactions

Many of the coupling reactions require a base such as OAc" or NEt3 in addition to the palladium. In the Heck reaction, for example, the base is used to effect elimination of hydrogen halide from an intermediate palladium complex, thus regenerating the palladium for use in further catalytic cycles. In the Suzuki reaction, on the other hand, the base binds to the boron atom of the boronic acid which activates the carbon-carbon bond for further reaction. 

The Suzuki-Miyaura cross-coupling reaction is a standard method for carbon-carbon bond formation between an aryl halide or triflate and a boronic acid derivative, catalyzed by a palladium-metal complex. As with the Mizoroki-Heck reaction, this cross-coupling reaction has been developed in ionic liquids in order to recycle and reuse the catalyst. In 2000, the first cross-coupling of a halide derivative with phenylboronic acid in [bmim] [BF4] was described. As expected, the reaction proceeded much faster with bromobenzene and iodobenzene, whereas almost no biphenyl 91 was obtained using the chloride derivative (Scheme 36). The ionic liquid allowed the reactivity to be increased, with a turnover number between 72 and 78. Furthermore, the catalyst could be reused repeatedly without loss of activity, even when the reaction was performed under air. Cross-coupling with chlorobenzene was later achieved - although with only a moderate yield (42%) - using ultrasound activation. 

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