Catalytic applications of CuII-containing MOFs based on N-heterocyclic ligand in the oxidative coupling of 2,6-dimethylphenol

Two CuII complexes bearing a N-heterocyclic ligand, namely [Cu(SO4)(pbbm)]n (1) and {[Cu(Ac)2(pbbm)] · CH3OH}n (2) (pbbm = 1,1′-(1,5-pentanediyl)bis-1H-benzimidazole) have been synthesized with the aim of exploiting new and potent catalysts. Single crystal X-ray diffraction shows that new polymeric complex 1 features 1-D double-chain framework. The catalytic studies on 1 and 2 indicate that they are efficient homogeneous catalysts for the oxidative coupling of 2,6-dimethylphenol (DMP) to poly(1,4-phenylene ether) (PPE) and diphenoquinone (DPQ) with H2O2 as oxidant and NaOMe as co-catalyst at room temperature. Optimal reaction conditions are obtained by examining the effects of solvent, the reaction time, temperature as well as the amounts of co-catalyst, catalyst and oxidant. Under the optimal conditions, the selectivity to PPE is almost up to 90% for both complexes, and the conversion of DMP is 85% for 1 and 90% for 2, comparable to those observed for highly active catalyst systems in the literature. Further comparison of their catalytic performances with those of the corresponding copper salt together with organic ligand, copper salt alone and free ligand reveals that the coordination of ligand to CuII ion plays a key role in generating the superior reactivities of complexes.

Graphical abstractTwo CuII-containing MOFs were synthesized and found to be highly effective catalysts for the oxidative coupling of 2,6-dimethylphenol (DMP) to poly(1,4-phenylene ether) (PPE) and diphenoquinone (DPQ) with H2O2 as oxidant and NaOMe as co-catalyst at room temperature. Under the optimized conditions, the selectivity to PPE is almost up to 90% for both complexes, and the conversion of DMP is 85% for 1 and 90% for 2, which can match those observed for the reported well-known catalysts.Figure optionsDownload full-size imageDownload as PowerPoint slide