A Discrete 3d–4f Metallacage as an Efficient Catalytic Nanoreactor for a Three-Component Aza-Darzens Reaction

Abstract

The exploration and development of coordination nanocages can provide an approach to control chemical reactions beyond the bounds of the flask, which has aroused great interest due to their significant applications in the field of molecular recognition, supramolecular catalysis, and molecular self-assembly. Herein, we take the advantage of a semirigid and nonsymmetric bridging ligand (H5 L) with rich metal-chelating sites to construct an unusual and discrete 3d–4f metallacage, [Zn2Er4(H2 L)4(NO3)­Cl2(H2O)]·NO3·xCH3OH·yH2O (Zn 2 Er 4 ). The 3d–4f Zn 2 Er 4 cage possesses a quadruple-stranded structure, and all of the ligands wrap around an open spherical cavity within the core. The self-assembly of the unique cage not only ensures the structural stability of the Zn 2 Er 4 cage as a nanoreactor in solution but also makes the bimetallic lanthanide cluster units active sites that are exposed in the medium-sized cavity. It is important to note that the Zn 2 Er 4 cage as a homogeneous catalyst has been successfully applied to catalyze three-component aza-Darzens reactions of formaldehyde, anilines, and α-diazo esters without another additive under mild conditions, displaying better catalytic activity, higher specificity, short reaction time, and low catalyst loadings. A possible mechanism for this three-component aza-Darzens reaction catalyzed by the Zn 2 Er 4 cage has been proposed. These experimental results have demonstrated the great potential of the discrete 3d–4f metallacage as a host nanoreactor for the development of supramolecular or molecular catalysis.

Impact of Host Flexibility on Selectivity in a Supramolecular Host-Catalyzed Enantioselective aza-Darzens Reaction

“… Moreover, the observed enantioselectivity in this transformation could serve as a sensitive measurement of the role that ligand design plays in host catalytic performance. In addition, a number of enantioselective aza-Darzens condensations catalyzed by chiral acids have been reported, − and recently, racemic aza-Darzens reactions have been explored in other host architectures, making this reaction an attractive, well-studied target to gain a deeper understanding of chiral host 1 . To this end, performing the aza-Darzens reaction with 2 mol % of enantiopure host 1 (R, ΔΔΔΔ) as a catalyst in 50% CD 3 OD/D 2 O (pD 8, 100 mM K 3 PO 4 ) provided excellent yield and enantioselectivity (99% NMR yield, 98% ee) for the trans -aziridine 3a (Table ).…”

“…In addition, a number of enantioselective aza-Darzens condensa-tions catalyzed by chiral acids have been reported, 54−56 and recently, racemic aza-Darzens reactions have been explored in other host architectures, making this reaction an attractive, well-studied target to gain a deeper understanding of chiral host 1. 57 To this end, performing the aza-Darzens reaction with 2 mol % of enantiopure host 1 (R, ΔΔΔΔ) as a catalyst in 50% CD 3 OD/D 2 O (pD 8, 100 mM K 3 PO 4 ) provided excellent yield and enantioselectivity (99% NMR yield, 98% ee) for the trans-aziridine 3a (Table 1). Testing multiple concentrations of CD 3 OD and D 2 O (pD 8, 100 mM K 3 PO 4 ) maintained this high selectivity for 3; however, running the reaction in pure CD 3 OD provided diminished yields and selectivity.…”

Visual and Real-Time Monitoring of Cd2+ in Water, Rice, and Rice Soil with Test Paper Based on [2 + 2] Lanthanide Clusters

“…Lanthanide materials have unique optical, − electrical, and magnetic properties , and are widely used in the area of luminescent sensing, − up-conversion, anti-counterfeiting inks, optics, and bio-imaging properties that are generated by the unique inner 4f electronics, − including stable and line-like emission bands, large Stokes displacement, and long luminescent lifetime . Lanthanide complexes, as efficient light-converting molecular devices, can combine the characteristics of organic ligands, which shows a wide absorption band and efficient energy transfer efficiency between the ligand and lanthanide ion, displaying very rich molecular design and synergistic “antenna effect”.…”

In Situ Electrochemical Reconstitution of CF–CuO/CeO2 for Efficient Active Species Generation

“…The industrialization of electrocatalysis is one of the most promising ways to achieve a sustainable supply of high-value-added chemicals and reduce the use of fossil fuels. − In the field of electrocatalysis, it is generally believed that the insufficient activity and poor selectivity and stability of electrocatalysts are the biggest obstacles to the industrialization of electrocatalytic technology, which motivates researchers to solve this criticism through the construction of electrode materials, optimization of electrolytes, design of electrolytic cells, and other approaches. − However, most of the current research mainly focuses on exploring new complicated materials to construct electrocatalysts, conversely ignoring the fundamental insight of the correlation between the intrinsic nature of the material and catalytic activity . In fact, most non-noble metal catalysts, especially transition metal oxides, exhibit satisfactory electrocatalytic activity under an efficient electrochemical reconfiguration. − Apparently, in situ electrochemical activation can optimize the chemical composition and electronic structure of a catalyst, prompting the exposure of more active sites, thereby further enhancing the electrocatalytic performance.…”