Polyoxovanadate-based MOFs: Multi-site efficient catalytic epoxidation of olefins

Catalytic epoxidation of olefins has garnered significant attention due to the important of epoxides as organic intermediates. Nevertheless, existing methodologies are often encumbered by environmental concerns, elevated costs, and the inability to achieve efficient epoxidation of both terminal and internal olefins concurrently. Consequently, to develop olefin epoxidation using oxygen as an oxidant under mild conditions has become a highly sought-after goal. In this paper, polyoxovanadates, which can activate oxygen, were employed as building units, and three isostructural polyoxovanadate-based metal-organic frameworks (POV-MOFs): M(azpy)V 2 O 6 (M=Co for 1 , Ni for 2 , and Zn for 3 ; azpy = 4, 4′-azobispyridine) were constructed. Single crystal diffraction analysis revealed that they comprised of transition metal M (Co 2 + , Ni 2+ , and Zn 2+ ) and {V 2 O 6 } 2- clusters. Among them, compound 1 , constructed by Co 2+ , exhibits clear advantages over compounds 2 and 3 , constructed by Ni 2+ and Zn 2+ , in catalyzing the selective oxidation of internal olefins and terminal olefins to the corresponding epoxides. At near room temperature , compound 1 can achieve 99 % conversion of internal olefin-type cyclooctene to cyclooctene oxide in 3 h, and 99 % selectivity, with 99 % conversion and 94 % selectivity of terminal olefin-type styrene to styrene oxide in 1.5 h. Further investigations revealed that both the Co²⁺ and the {V₂O₆} cluster in compound 1 all can independently catalyze the epoxidation of olefins.