2D Hybrid Architectures Constructed from Two Kinds of Polyoxovanadates as Efficient Heterogeneous Catalysts for Cyanosilylation and Knoevenagel Condensation

The design of heterogeneous catalysts for highly efficient catalysis for cyanosilylation reactions and Knoevenagel condensations is greatly significant, due to the important application of their products in industry. Herein, five hybrid compounds constructed from two types of polyoxovanadates, [MV12O38]12- (M = Ni, Mn) and [V10O28]6-, were successfully synthesized as heterogeneous catalysts for both reactions, which are {(dpdo)[Ln2(H2O)9(dpdo)][Ln(H2O)5]2[Ln(H2O)4]2[V10O28][NiV12O38]·nH2O} (1, Ln = La, n = 23; 2, Ln = Ce, n = 27; 3, Ln = Pr, n = 27; dpdo = 4,4'-bipyridine N,N'-dioxide) and {(dpdo)[Ln2(H2O)9(dpdo)][Ln(H2O)5]2[Ln(H2O)4]2[V10O28][MnV12O38]·27H2O} (4, Ln = La; 5, Ln = Pr). These compounds were characterized by IR spectroscopy, elemental analysis, TG analysis and X-ray diffraction (single crystal and powder) etc. Compounds 1-5 have similar 2D hybrid structures, in which isopolyvanadate [V10O28]6- and heteropolyvanadate [MV12O38]12- are linked together by hydrated Ln3+ cations and Ln-dpdo coordination complexes. Polyoxovanadates [V10O28]6- and [MV12O38]12- both originate from the transformation of the [MV13O38]7- raw material. This kind of extended structure containing isopolyvanadate and heteropolyvanadate has never been reported hitherto. Because of the Lewis acidity of the Ln3+ cation and the Lewis basicity of the polyoxovanadates, all five compounds exhibit excellent catalytic performance in cyanosilylation and Knoevengel condensation reactions. Especially, compound 3, with a Pr3+ cation, displayed the best catalytic results. Furthermore, these catalysts exhibit a truly heterogeneous nature and good recyclability.