Heck Reaction Catalyzed by Mesoporous SBA-15-Supported Ionic Liquid-Pd(OAc)₂

Abstract

Palladium acetate was immobilized into the pores of modified SBA-15 with absorbed ionic liquid. The immobilized catalyst system was studied for Heck coupling. The catalyst exhibited high catalytic activity in the coupling of aryl iodides and activated aryl bromides with acrylates. Moreover, it could be recycled without significant loss of activity.

Key words

Heck reaction - palladium - immobilization - ionic ­liquid - SBA-15

References and Notes

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8

Modification of SBA-15 with Ionic Liquid: To a solution of N-1-(3-triethoxysilylpropyl)-3-methylimidazolium chloride (0.77 g, 2.4 mmol) in toluene was added SBA-15 (2.0 g). The mixture was stirred at 105 ˚C for 12 h. After cooling, the reaction mixture was filtered and washed completely with CH₂Cl₂, and dried at 90 ˚C under vacuum to yield modified SBA-15 2 (2.48 g). Elemental analysis and weight gain showed that 1.05 mmol of the ionic liquid was anchored on 1.0 g of 2.

9

Immobilization of Pd(OAc) ₂ onto Modified SBA-15 2: To a stirred solution of Pd(OAc)₂ (60 mg, 0.4 mmol) and 1-butyl-3-methylimidazolium hexafluorophosphate (100 mg, 0.42 mmol) in THF (10 mL), modified SBA-15 2 (1.0 g, 1.05 mmol/g) was added. The mixture was stirred for 1 h at r.t., and then THF was removed under reduced pressure. The resulting powder was dried under vacuum at 90 ˚C to give SBA-15-supported ionic liquid-Pd(OAc)₂ 3 (1.15 g). ICP analysis showed that 0.21 mmol of Pd was immobilized on 1.0 g of 3.

10

General Procedure for the Heck Reaction: Reaction was carried out in a 5-mL glass vial equipped with a Teflon screw cap. A mixture of aryl halide (1.0 mmol), acrylate (1.3 mmol), Bu₃N (1.5 mmol), and catalyst 3 (1.0 mol%) in dodecane (1.5 mL) was stirred at 120 ˚C. The reaction was periodically monitored by GC analysis. The mixture was diluted with Et₂O (15 mL) and H₂O (3 mL). Catalyst 3 was separated from the mixture and washed with H₂O and Et₂O. The ethereal layer was dried over MgSO₄ and then evap-orated under reduced pressure. The residue was purified by column chromatography on silica gel.