Cyclodextrin Polymers: Efficient and Specific Catalysis of the Suzuki-Miyaura Cross-Coupling Reaction

Abstract

Transition metal-catalyzed C-C couplings have the potential to provide complex molecules, however, the formation of selective C–C bonds for symmetric/unsymmetric dihalogenated aromatics remains being a challenge. To explore the specificially selective Suzuki monocoupling of symmetrical/unsymmetrical dibromopyridines, a set of cross-linked cyclodextrin polymers (CD-P) were synthesized by CuAAC reaction and coordinated with Pd (CD-P-Pd (II)). Numerous cavities with pocket-like catalytic sites were designed in its structure and the narrow rims of cyclodextrin were connected and enclosed by triazole rings coordinated with Pd. Meanwhile, the wide rims were kept open to recognize the reactants and products for association and dissociation with the cavity. The use of CD-3-P-Pd (II) under mild conditions can obtain monosubstituted products with yield of up to 79% and specific selectivity (mono−/bis- = 100:0 for symmetrical dibromopyridines, monoaty−/monoty−/bis- = 80:0:20 for unsymmetrical dibromopyridines). This mechanism study supports the hypothesis that the first oxidation addition step can be effectively regulated by the structural design of the catalyst to obtain monosubstituted products. Cyclodextrin polymers offered exciting possibilities for the specificity of coupling reactions by facilitating host-guest recognition.