Abstract
A well-designed and synthesized water-soluble class of β-cyclodextrin supported palladium complex PdLn@Et-β-CD could efficiently validate high catalytic activity and act as a supramolecular platform for phosphine-free Suzuki–Miyaura cross-coupling reactions between arylboronic acid/arylboronic ester and aryl halides in water under mild conditions. The presented novel PdLn@Pr-β-CD complex catalyst was characterized by NMR, XRD, FT-IR, and DSC analysis. Furthermore, the role of the PdLn@Et-β-CD fragment in the reaction mechanism studied by molecular complexation was proposed based on FT-IR, 2D NMR (ROESY) spectroscopy, FE-SEM, and DSC spectroscopic analysis. The important benefits of this technique comprise simple phosphine-free preparation of the palladium catalyst, a wide range of functional-group tolerance, and easy recyclability; this method, furthermore, eschews hazardous reagents or solvents.
Highlights
The Suzuki–Miyaura cross-coupling reaction is the most widely used protocol for the formation of carbon–carbon bonds and has become the predominant approach in the synthesis of biaryl [1,2,3], resulting in an extensive range of natural products and pharmaceuticals
NaOH, which was further reacted with ethylenediamine at aqueous
In the Differential scanning calorimetry (DSC) curve of the BN/PdLn@Et‐β‐CD inclusion complex, the endothermic peak of free BN had clearly disappeared. These results suggest that the formation of the endothermic peak of free BN had clearly disappeared
Summary
The Suzuki–Miyaura cross-coupling reaction is the most widely used protocol for the formation of carbon–carbon bonds and has become the predominant approach in the synthesis of biaryl [1,2,3], resulting in an extensive range of natural products and pharmaceuticals. The expansion of phosphine-free catalytic systems to overcome the above problems is considered to be one of the most demanding and challenging areas of organic synthesis [7]. With these issues in mind, many catalytic systems have been developed using various carriers to immobilize Pd catalysts, for example silica [8], Pd/C [9], magnetic nanoparticles [10,11,12], carbon nanotubes [13], nanomaterials [14,15,16], polymers [17,18], and cyclodextrins [19]. Cyclodextrins (CD) have recently attracted abundant attention for Suzuki–Miyaura coupling reactions, given that phosphine free CD ligands support Pd catalytic systems [20,21,22,23,24]
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