Fabrication of heterogeneous Zr-containing polyoxometalate as an efficient catalyst for the synthesis of a broad range of 1,5-benzodiazepine derivatives

As an extension of our interest in polyoxometalate (POM) as catalysts, one heterogeneous catalyst TBA8[Zr(W5O18)2]middot17H2O (Zr(W5)2) (TBA+: tetrabutylammonium) was synthesized and fully characterized by multiple spectroscopic techniques. In this catalyst, zirconium ion connected to two mono-lacunary Lindqvist [W5O18 ]4- anions to create anionic sandwich-type POM and this anionic unit was encapsulated by TBA+ cations to form heterogeneous catalyst with hydrophobic nature. It is assumed that alkyl chains of TBA+ can trap reactants on the surface of catalyst, thus in this regard, the probability of the interaction between reactants and POM center can increase which lead to the higher catalytic efficiencies of above catalysts. Using Zr(W5)2 as a heterogeneous and efficient catalyst, a series of 1,5-benzodiazepines were synthesized via four mild and solvent-free reactions such as reaction of 1,2-phenylenediamine with ke-tones, chalcones, 1,3-diketones and aldehydes. According to the results, the presented protocol is superior to the previously reported methodologies in terms of reaction time and product yield. The facile work-up procedure and the reusability of this catalyst are other advantages of this protocol.(c) 2022 Elsevier B.V. All rights reserved.

Automated summary

A new heterogeneous catalyst, TBA8[Zr(W5O18)2]middot17H2O (Zr(W5)2), was synthesized and characterized. It was found that the catalyst had a sandwich-type structure consisting of zirconium ions and mono-lacunary Lindqvist [W5O18 ]4- anions, encapsulated by TBA+ cations. This catalyst exhibited hydrophobic properties and improved catalytic efficiency by trapping reactants on its surface. Using Zr(W5)2 as a catalyst, a series of 1,5-benzodiazepines were successfully synthesized via mild and solvent-free reactions.