Immobilized Lanthanum(III) Triflate on Graphene Oxide as a New Multifunctional Heterogeneous Catalyst for the One-Pot Five-Component Synthesis of Bis(pyrazolyl)methanes

In this work, immobilized lanthanum(III) triflate on graphene oxide as a new multifunctional heterogeneous catalyst has been synthesized. The structure of immobilized lanthanum(III) triflate on amine-grafted graphene oxide [La(OTf)2-grafted-GO] was established by FT-IR, XPS, and solid-state 13C MAS NMR. The morphology and distribution of elements on La(OTf)2-grafted-GO was determined by FESEM, TEM, and EDS images. La(OTf)2-grafted-GO was tested as the first reusable (Lewis and Brønsted) acid–base multifunctional catalyst for the efficient one-pot five-component synthesis of bis(pyrazolyl)methanes. This multifunctional catalyst exhibits a high synergic effect in this one-pot tandem reaction. Due to the uniform spreading of the active sites along with the crumpling structure of the catalyst, reactants and products can simply move toward the catalytic active sites on the surfaces of the catalyst without significant mass-transfer limitation. These properties increase the catalytic activity of La(OTf)2-grafted-GO. Moreover, the catalyst was readily recycled and reused 9 times. The morphology and structure of La(OTf)2-grafted-GO remained intact after 9 recoveries according to the FT-IR spectrum and TEM image of the used catalyst.

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