Polyoxometalate catalyzed imine synthesis: Investigation of mechanistic pathways

Abstract

The syntheses of imines by oxidative coupling of primary alcohols and amines were achieved by using 2 mol% polyoxometalate (POM) Na12[WZn3(H2O)2(ZnW9O34)2] (ZneWZn3) catalyst in the presence of t- BuOK and di-oxygen with excellent conversion (up to 100%) and selectivity (up to 100%). Non-noble metal-based POM catalyst in the presence of base represents a new reaction protocol for the selective synthesis of imine from both aromatic and aliphatic primary amines with functional group tolerance. Control experiment shows the formation of di-oxygen bind ZneWZn3 activated species. The electrondensity of POM is mostly situated on the surface oxygen atoms of WeOeW bonds which can engage the alcoholic OH group and helps for the imine selectivity in the second step of imine synthesis.