Iron Complexes Anchored onto Magnetically Separable Graphene Oxide Sheets: An Excellent Catalyst for the Synthesis of Dihydroquinazoline-Based Compounds

In
this work, a green, sustainable, and efficient protocol for
the syntheses of dihydroquinazoline derivatives is proposed. Initially,
three Schiff base complexes of iron containing the ligand (2,2-dimethylpropane-1,3-diyl)­bis­(azanylylidene)­bis­(methanylylidene)­bis­(2,4-Xphenol),
where X = Cl (complex 1)/Br (complex 2)/I
(complex 3), were synthesized, fully characterized, and
used in the desired syntheses. Complex 1 excelled as
a catalyst, closely followed by complexes 2 and 3. DFT calculations helped in rationalizing the role of the
halide substituent in the ligand backbone as a relevant factor in
the catalytic superiority of complex 1 over complexes 2 and 3 for the synthesis of the dihydroquinazoline
derivatives. Finally, to facilitate catalyst recoverability and reusability,
complex 1 was immobilized on GO@Fe3O4@APTES (GO, graphene oxide; APTES, 3-aminopropyltriethoxysilane)
to generate GO@Fe3O4@APTES@FeL1 (GOTESFe).
GOTESFe was thoroughly characterized through scanning electron microscopy,
transmission electron microscopy, powder X-ray diffraction, Fourier
transform infrared spectroscopy, thermogravimetric analysis, and X-ray
photoelectron spectroscopy and efficiently used for the synthesis
of dihydroquinazoline derivatives. GOTESFe could be magnetically recovered
and reused up to five cycles without compromising its catalytic efficiency.
Therefore, immobilization of the chosen iron complex onto magnetic
GO sheets offers an extremely competent route in providing a blueprint
of a readily recoverable, reusable, robust, and potent catalyst for
the synthesis of dihydroquinazoline-based compounds.