Praseodymium-selenium connecting selenotungstate containing mixed building blocks for catalytic synthesis of aza-heterocycles

Abstract

A novel praseodymium-selenium connecting selenotungstates [Pr2.5(SeO)(SeO3)0.25(mal)(W4O9)(SeW8O32)(SeW9O33)2(H2O)4]16- (BC-Pr) (H3mal = DL-malic acid) was synthesized in acidic aqueous solution. The skeleton of BC-Pr is formed by two {SeW9} and one {SeW8} building blocks encapsulating a {Pr2Se2W4(mal)} unit. Two adjacent trimers are bridged by Pr3+, {SeO3} and mal to construct a hexamer that is alternately connected through Pr-O-W bonds to form one-dimensional chains. Its remarkable structural feature lies in its inclusion of two building block types and selenium acts as both heteroatom and linkage, which are extremely rare in selenotungstates chemistry. In addition, BC-Pr exhibits excellent catalytic activity for the cyclization of 2-aminobenzamides/2-aminobenzenesulphonamides with aldehydes under green and mild conditions, leading to the synthesis of a series of 2,3-dihydroquinazolinones and 3,4-dihydro-2H-1,2,4-benzothiadiazine-1,1-dioxides with high yields. The present study provides comprehensive insights into the novel fabrication of lanthanide-substituted POMs and their immense potential in environmentally friendly synthesis of aza-heterocycles.