Effect of Water on Arylboronic Acid Mediated Cross-Coupling Reaction

We studied the effect of water on the palladium acetate-catalyzed coupling reaction of aryl boronic acid with aryl bromide or acyl chloride in ionic liquid or PEG, and found that water had a remarkable rate accelerating effect on the Suzuki reaction and Suzuki-Type reaction when other reaction conditions were uniform. The ratio of water to IL or PEG was pivotal to the reaction, and the optimal ratio of water to IL or PEG was different to the Suzuki and Suzuki-Type reactions. When the ratio of [bmim][PF6] and water was 3∶1, the best yield of 99% of Suzuki reaction was achieved, while the optimal ratio of [bmim][BF4] to water was 3∶3(93%). The Suzuki-Type reaction delivered the good yield of 82% in the [bmim][PF6]-H2O system when the mass ratio of [bmim][PF6] to water was 3∶2.5, while in the PEG-H2O system, the optimal ratio of PEG to water was 3∶3(yield was 94%). The possible mechanism of water influence on the cross-coupling reaction was discussed.