Polyoxometalate-Based Metal–Organic Frameworks with Both Proton Acid and Multioxidative Active Sites: Highly Efficient Catalytic Synthesis of Quinazolinones

Quinazolinone derivatives are an important class of pharmaceutical
and pesticide intermediates, which are generally synthesized starting
with the condensation reaction between aldehydes and 2-aminobenzamide
to obtain corresponding intermediates and then oxidized to obtain
the products. Although some catalysts have been developed currently
for the synthesis of quinazolinone derivatives, their catalytic efficiency
is relatively low because only the oxidative catalytic sites of the
catalyst have been focused on. Herein, we synthesized three new polyoxometalate-based
metal–organic frameworks, [CuI4(4,4′-bipy)7(Hn–1PMo12–nVnO40)]·2H2O (n = 1–3), which were formed by
coordinating a Cu(I)-bipy complex with different Keggin-type phosphomolybdic
acids. An important feature of these compounds is that they possess
proton and multioxidative active sites [Cu(I) center and V(V) center];
thus, we applied them to the catalytic synthesis of quinazolinone
derivatives. The results indicate that compound 3 has
an excellent catalytic activity. Based on density functional theory
calculations, it is speculated that protons participate in the aldehyde
amine condensation reaction, which changes the reaction pathway and
reduces the activation energy from 55.1 to 31.4 kcal/mol, thereby
increasing the reaction rate significantly. Interestingly, Raman spectra
and electron paramagnetic resonance measurements indicate the presence
of CuIIOO• and •O2– during the oxidative dehydrogenation process,
which facilitates the rapid consumption of 2-phenyl-2,3-dihydroquinazolin-4(1H)-one intermediates, thereby promoting the chemical reaction
to move toward the positive direction. Thanks to the synergistic effect
of multicatalytic sites, compound 3 achieved highly efficient
catalytic synthesis of quinazolinones with 99% yield in 1 h.