Cooperative Heterogeneous Catalysis with a Robust Acid–Base Bifunctional Zinc-Based Metal–Organic Framework Nanostructure in the Diastereoselective Henry Reaction
Vandana Sharma, Sanjay K. Mandal
Abstract
The diastereoselective Henry (nitroaldol) reaction is a dominant tool for the synthesis of β-nitroalcohols that are crucially important by themselves and are potent intermediates for diversely functionalized pharmaceutical drugs. In the present work, we strategically explored an l -glutamic acid-based tricarboxylate, viz., ( S )-2-[(4-carboxybenzyl)amino]pentanedioic acid [H 3 ( l -GluBenz)], to make a highly robust and microporous 3D metal–organic framework, [Zn 4 (H( l -GluBenz)) 4 (H 2 O) 2 ] n [ Zn-( l -GluBenz) ], under solvothermal conditions. Zn-( l -GluBenz) was structurally characterized by various analytical techniques to indicate the presence of a rare Zn 4 (−COO) 6 secondary building unit. Utilizing the cooperative Bronsted basic −NH sites from the ligand and unsaturated Lewis acidic metal centers present in the framework, Zn-( l -GluBenz) was found to be a very efficient bifunctional heterogeneous catalyst for the Henry reaction at room temperature. It is noteworthy to mention that, compared to any catalyst reported in the literature for this reaction, Zn-( l -GluBenz) exhibits better activity with a minimal amount of nitroethane, catalyst amount, and time. In addition to generating a broad substrate scope with various aromatic aldehyde derivatives, the excellent recyclability and stability of the catalyst are also reported.