Supported phase-transfer catalysts as selective agents in biphenyl synthesis from haloaryls

Coupling of substituted halobenzenes to the respective biphenyls is effected with high selectivity in toluene, using a combination of a reducing agent and a weak base in the presence of catalytic tetrabutylammonium bromide (TBAB) and palladium that are both supported on carbon. The maximum selectivity to biphenyl was achieved when Pd, Na2CO3, and TBAB were all supported together on activated carbon. The results are explained with postulation of a physical micro-membrane formed in situ by the phase-transfer catalyst.