Engineering a Nanoscale Primary Amide-Functionalized 2D Coordination Polymer as an Efficient and Recyclable Heterogeneous Catalyst for the Knoevenagel Condensation Reaction

Abstract

This work reports the design, structural characterization, and catalytic behavior of the first example of primary amide-functionalized coordination polymers (CPs), namely, {[Cd 2 (2-bpbg)(fum) 2 (H 2 O) 2 ]•8.5H 2 O} n (1) (where 2-bpbg = N,N′-bis(2-pyridylmethyl)-1,4-diaminobutane-N,N′-diacetamide and fum = fumarate). CP 1 is synthesized from a one-pot selfassembly of starting materials in methanol under ambient conditions in excellent yield and purity, allowing an easy access to multigram quantities of it within few hours. As an example, CP 1 was used as a highly efficient heterogeneous catalyst in the carbon−carbon bond-forming Knoevenagel condensation reaction for the conversion of benzaldehyde to benzylidene malononitrile. CP 1 possesses both Lewis acidic and Brønsted basic character for the presence of unsaturated metal sites and primary amide groups, respectively, making it a highly competent bifunctional catalyst for such type of reactions. Surprisingly, on the one hand, 100% conversion was observed using only 2 mol % catalyst within 1 h at 27 °C in methanol. On the other hand, 2 mol % and 3 mol % catalyst loadings but without a solvent gives 93% and 100% conversions, respectively, in 1 h at 27 °C. CP 1 is far better than those reported in the literature. To prove the uniqueness and efficiency of the primary amide-based ligand, a similar compound with a pyridyl-based ligand was also synthesized, {[Cd 2 (tpbn)(fum) 2 ]•6H 2 O} n (2) (where tpbn = N′,N′,N″,N″-tetrakis(pyridin-2-ylmethyl)butane-1,4-diamine). With CP 2 under the same catalyst loading and conditions (2 mol %, 27 °C, 1 h), only 28% conversion was observed. This demonstrates that selective heterogeneous catalytic properties of 1 over 2 are due to the presence of the primary amide moieties and open metal sites. Moreover, CP 1 can easily be separated from the reaction mixture and reused for five consecutive cycles without significant loss of its activity. Both 1 and 2 were fully characterized by elemental analysis, infrared spectroscopy, thermogravimetric analysis, and single-crystal and powder X-ray diffraction. These crystallize in the triclinic P1̅ space group, showing their isostructural nature and three-connected, uninodal {6 3 } honeycomb net topology.

Template-Induced {Mn2}–Organic Framework with Lewis Acid–Base Canals as a Highly Efficient Heterogeneous Catalyst for Chemical Fixation of CO2 and Knoevenagel Condensation

“…On the basis of the previously reported theoretical calculations and our experimental studies, − one inferential catalytic mechanism for the cycloaddition reaction is listed in Figure . First, epoxide will be polarized by exposed open metal sites offered by {Mn III 2 } SBUs on the inner wall.…”

Tunable Strategies Involving Flexibility and Angularity of Dual Linkers for a 3D Metal–Organic Framework Capable of Multimedia Iodine Capture

“…This reversibility based on the polarizing ability of a moiety is feasible as the process does not involve bond formation with the host framework, unlike in the case of halogen bond introduction. , In view of the fact that an oxadiazole moiety (two nitrogen and one oxygen heteroatoms in the ring) in a linker was found to create an induced dipole in polar molecules, such as CO 2 , − we chose to design a three-dimensional (3D) MOF using a dicarboxylate linker containing an oxadiazole moiety as the central core for the current study. In attempts to synthesize various MOFs for different targeted applications, we have earlier demonstrated the effect of systematic ligand and linker alteration on their sensing, sorption, and catalytic abilities. ,− In this regard, one of the important aspects is the role played by bis­(tridentate) polypyridyl ligands and their derivatives, spanning between two metal centers , that can be termed as the dimetal subunit having open coordination sites on either end, in the formation of diverse frameworks. It should be noted that the use of flexible bis­(tridentate) ligands has always been a challenge to make desired three-component MOFs (the third component being a multitopic carboxylate linker) as these prefer wrapping around a metal center to satisfy its coordination availability.…”

Design and Development of a Heterogeneous Catalyst for the Michael Addition of Malononitrile to 2-Enoylpyridines: Influence of the Primary Amide Decorated Framework on Catalytic Activity and Selectivity

“…Materials and methods, physical measurements, and details for single-crystal and powder X-ray diffraction are provided in the Supporting Information. The tpbn and 2-bpbg ligands were prepared by following our previously reported procedure. , For catalytic application, the β-substituted 2-enoylpyridines and other substrates were prepared according to procedures known in the literature …”

“…In view of this, we have envisioned that a coordination network catalyst with a primary amide functionality can be a feasible heterogeneous catalyst for such reaction. This is based on our recent demonstration of Friedel–Crafts alkylation and Knoevenagel condensation reactions . For the 2-enoylpyridine substrate, the primary amide side arm in a ligand of a coordination network can form a hydrogen bonded seven-membered cyclic motif R 2 2 (7), containing both N–H bonds from the NH 2 group, which is more favorable compared to the homogeneous organocatalyst where the two N–H bonds come from the urea moiety (Scheme ).…”