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

Abstract

A novel praseodymium–selenium connecting selenotungstate [Pr_2.5(SeO)(SeO₃)_0.25(mal)(W₄O₉)(SeW₈O₃₂)(SeW₉O₃₃)₂(H₂O)₄]¹⁶⁻ (BC-Pr) (H₃mal = DL-malic acid) was synthesized in an acidic aqueous solution. The skeleton of BC-Pr is formed by two {SeW₉} building blocks and one {SeW₈} building block 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 a heteroatom and linkage, which is extremely rare in selenotungstate 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 (DHQZs) and 3,4-dihydro-2H-1,2,4-benzothiadiazine-1,1-dioxides (DHBDs) in 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.