Ln-substituted polytungstates as efficient hetergeneous catalysts for Knoevenagel condensation reaction

Three isomorphic polytungstates, Cs9K18H10{[Sm2(H2O)4W4O10(AsW9O33)3]2(N(CH2PO3)2)}∙46.5H2O (1), Cs10K9H18{[Eu2(H2O)4W4O10(AsW9O33)3]2 (N(CH2PO3)2)}∙41.5H2O (2), Cs10K9H18{[Gd2(H2O)4W4O10 (AsW9O33)3]2(N(CH2PO3)2)}∙46H2O (3), have been successfully synthesized and characterized by routine methods, and demonstrated excellent catalytic activities in Knoevenagel condensation reaction as heterogeneous catalysts. Notably, catalyst 1 achieved higher reaction activity than catalysts 2 and 3, where a satisfactory reaction yield (95%) and high TON value (6380) could be obtained at moderate reaction condition. In addition, in the scale-up experiment, with the help of catalyst 1, 7.8 g benzaldehyde and 5.7 g ethyl cyanoacetate could transform into corresponding condensation product with a satisfactory yield (83%) and impressive TON value (13883).