Hydrogen bond-mediated polyoxometalate-based metal-organic networks for efficient and selective oxidation of aryl alkenes to aldehydes

Selective oxidation of aryl alkenes to aldehydes is an important approach to produce industrial raw materials, in which the exploration of an efficient heterogeneous catalyst is significant but challenging. In this work, three hydrogen bond-mediated polyoxometalate(POM)-contained metal–organic networks with the formulas of [Ni(BTD) 2 (H 2 O) 2 ] 2 [SiW 12 O 40 ]·12H 2 O ( 1 ), [Ni(BTD) 2 (H 2 O)] 2 [SiW 12 O 40 ]·6H 2 O ( 2 ) and [Zn(BTD) 2 (H 2 O)] 2 [SiW 12 O 40 ]·6H 2 O ( 3 ) (BTD = 4H,4ʹH-[3,3ʹ-bi(1,2,4-triazole)]-5,5ʹ-diamine) were hydrothermally synthesized, in which the metal–organic fragments interact with POM clusters via abundant hydrogen bonding to extend the structure into three-dimensional supramolecular networks. To be explored as heterogenous catalysts, compounds 1 – 3 showed high catalytic activity and selectivity for the selective oxidation of styrene to benzaldehyde. Among them, compound 1 exhibits the highest performance with ca. 99% styrene conversion and ca. 99% selectivity of benzaldehyde in 5 h. Moreover, compound 1 displays rich substrate compatibility, recyclability and good structural stability. A series of experiments demonstrated that the high performance of compound 1 should be attributed to the synergistic effect among polyoxoanion and coordination-unsaturated metal centers in metal–organic fragments, which facilitates the activation of H 2 O 2 and styrene substrates, thus enhancing the catalytic performance.