Oxadiazoline and ketoimine palladium(II) complexes supported on a chitosan membrane and their catalytic activity for the microwave-assisted Suzuki–Miyaura cross-coupling in water

The fused bicyclic Δ4-1,2,4-oxadiazoline trans-() palladium(II) complex 1 (R = p-ClC6H4), in refluxing chloroform, undergoes N–O bond cleavage of the oxadiazoline ring to furnish the new ketoimine palladium(II) complex trans-() 2 bearing the 4-chloro-N-(5,5-dimethylpyrrolidin-2-ylidene)benzamide ligands. Complexes 1 (R = Me) and 2 (R = p-ClC6H4) were immobilized on a chitosan membrane and the systems acted as supported-catalysts (Pd-chit 1 and Pd-chit 2, respectively) for the model microwave-assisted Suzuki–Miyaura cross-coupling reactions in water using p-bromoanisole and phenylboronic acid to give p-methoxybiphenyl in excellent yield. The effects of catalyst loading, temperature, time, the phase-transfer agent tetrabutylammonium bromide (TBAB) and base were investigated, and the supported catalyst was recovered and reused up to seven times, with a gradual loss of catalytic activity.

Graphical abstractFigure optionsDownload full-size imageDownload high-quality image (136 K)Download as PowerPoint slideHighlights► Chitosan supported Pd catalysts for microwave-assisted Suzuki–Miyaura couplings in water. ► High catalytic activity even in the presence of lower catalyst loadings in comparison with other supported palladium sources. ► Effects of catalyst loading, temperature, time, phase-transfer agent and base were investigated. ► Environmentally friendly microwave protocol.