Role of Amine in Arylation of Ethylene with Iodobenzene Catalyzed by Rhodium Trichloride

Rhodium trichloride effectively catalyzes the arylation of ethylene with iodobenzene in the presence of an amine to give styrene, although neither rhodium-powder nor chlorotris(triphenylphosphine)rhodium(I) is effective. The efficacy of the amine in increasing the yield of styrene is remarkable with tertiary and secondary amines but negligible with a primary amine. The difference among these amines in their interaction with rhodium trichloride is explained by their steric hindrance based on the isolation of the Rh(III)–amine complex only with primary amine.