Heterogeneous Rh/C-catalyzed direct reductive coupling of haloaryls to biaryls in water

Reductive coupling of haloaryls and substituted haloaryls to the respective biaryls is effected in water with good selectivity, using a reducing agent such as formate salts and a base, NaOH, in the presence of a catalytic amount of PEG-400 and 5% Rh/C catalyst at 115 °C temperature. The catalyst can be recycled. The competing reduction reaction is minimized with proper alteration of the operating conditions. The role of temperature, catalyst loading, reducing agents, base, and PEG-400 are discussed. The reaction follows a zero-order kinetics.