Sol–gel entrapped dichlorobis(triphenylphosphine)palladium as an efficient recyclable catalyst for the cross-coupling of aryl halides with indium- and related alkylating reagents

Physically entrapped dichlorobis(triphenylphosphine)palladium(II) within a silica sol–gel matrix is an efficient catalyst for cross-coupling of aryl iodides, bromides and triflates with intramolecularly stabilized dimethyl- and diethylindium alkylating reagents. The coupling reactions take place in benzene or toluene and depend both on the electronic and steric nature of the substrate, and on the electronic structure of the encaged palladium complex. The immobilized catalyst is leach proof and can be recycled at least four times without significant loss of its activity. The catalyst promotes also the Suzuki coupling of aryl halides with phenylboronic acid and the Stille reaction with tributylphenyltin. In aromatic hydrocarbon solvents both cross-coupling and homocoupling take place as the major and minor processes, respectively. In dioxane homocoupling becomes more significant on account of the desired cross-coupling reaction.