Amide functionalized metal–organic frameworks for diastereoselective nitroaldol (Henry) reaction in aqueous medium

Abstract

The two new metal-organic frameworks (MOFs) of zinc(II) and copper(II) [Zn 2 L 2 (1,4-BDC)] n ⋅ ⋅ ⋅ ⋅2n(DMF) (1) and [Cu(L) 2 ] n .4n(DMF).n(H 2 O) (2) (L = 4-(pyridin-4ylcarbamoyl)benzoate; BDC = benzenedicarboxylate), respectively, have been synthesized from a pyridyl amide functionalized benzoic acid (HL). They were characterized by elemental, FT-IR, thermogravimetric, powder X-ray and single crystal X-ray diffraction analyses. Single crystal Xray crystallography reveals that 1 and 2 exhibit 2D and 3D polymeric architectures, respectively.Topological analysis illustrate a 6-connected pcu alpha-Po primitive cubic for 1 and a 8connected body centred cubic (bcu) topology for 2. Both 1 and 2 act as heterogeneous catalysts for the nitroaldol reaction in aqueous medium, with a high yield and moderate to good diastereoselectivities under ambient conditions. They can be recycled and reused without any significant loss of the catalytic efficiency. IntroductionThe design and construction of metal-organic frameworks (MOFs) 1 , also known as coordination polymers (CPs), have attracted enormous attention owing, e.g., to their simplistic preparation, 2 structural diversity, tunable pore metrics and easy functionalization of their surfaces. As a result,MOFs have found widespread applications in storage of fuel and environmental gases, 2,3 molecular separation, 4 luminescence, 5 magnetism, 6 drug delivery, 7 biomedical imaging 8 and sensing. 9 Recently, MOFs have found applications in the field of catalysis, 10-15 where their high density of active sites and high porosity can be advantageous features. Usually, the catalytic activity of MOFs is dependent, e.g., on the Lewis acidity of the metal cations, 12 the presence of basic groups 13,14 (such as pyridine, amide and amine) in constructing linkers and the redox properties of the metal centres. 10,11,15 Thus, in pursuing our interest on the synthesis of MOFs for possible application in catalysis, 10-14 we chose 4-(pyridin-4-ylcarbamoyl)benzoic acid (HL) as a ligand source ( Fig. 1), based on the following reasons: (i) the amide backbone in the ligand framework may provide a basic environment which may facilitate the catalytic reaction 13b,16 ; (ii) the ligand comprises multiple coordinating groups which should be suitable for building extended frameworks with a large surface area, also favourable for catalysis. Concerning a possible catalytic application, the nitroaldol (or Henry) reaction is as an important carbon-carbon bond formation reaction and widely used in organic synthesis. 11,17-20 The resulting α-hydroxy nitro compounds are valuable starting materials for, e.g., 1,2-amino alcohols or βhydroxy acids. 21 Generally, such a reaction is performed with homogeneous basic catalysts, such as alkali metal hydroxides, alkoxides or amines, with a good efficiency. 22 A number of homogeneous catalysts have already been reported by our group for such a type of reaction. 10a,11,23 However, heterogeneous catalysts for such a transformation are scant, 10a,11d-g,24-28 and thus we ...

Hydrosoluble Complexes Bearing Tris(pyrazolyl)methane Sulfonate Ligand: Synthesis, Characterization and Catalytic Activity for Henry Reaction

“…The results show that the aromatic aldehydes with electron-donating substituents (OCH 3 or CH 3 , Table 3, entries 1-4) exhibit a lower reactivity than those bearing electron-withdrawing groups (NO 2 , Br or Cl, Table 3, entries 7-12) due to the higher electrophilicity of the aldehyde in the latter case. In comparison to the scarce examples found in the literature for the catalytic nitroaldol reaction in water, using catalysts based on different metals (Table S3), the conversions obtained in this work are comparable, or better in some cases, taking into consideration the indicated reaction conditions such as temperature, amount of catalyst, and reaction time [43,44,[60][61][62][75][76][77][78][79][80]. Based on the study of several variables, it was found that the best reaction conditions to obtain the highest possible yield of β-nitro alcohols using catalyst 1 (5 mol%) is by heating the reaction mixture at 100 ºC for 48 h in a mixture of water and MeOH.…”

“…Activation of the carbonyl group using Lewis acidic metal compounds for catalytic Henry reaction is an approach that has been intensively studied and performed with (i) a well-defined complex [28,[43][44][45][46][47][48][49][50][51][52][53], (ii) an in situ generated complex by addition of a metal salt and a ligand [54][55][56][57][58][59], or (iii) a metal organic framework (MOF) [60][61][62]. In some instances a base is used to facilitate the deprotonation of the nitroalkane [56,63,64].…”

Synthesis of Metallomacrocycle and Coordination Polymers with Pyridine‐Based Amidocarboxylate Ligands and Their Catalytic Activities towards the Henry and Knoevenagel Reactions

“…The same reaction catalyzed by a Cu II –pyridine–2,3,5,6‐tetracarboxylate framework led to a yield of 78 % after 36 h (Table S6, entry 8) . However, a 2D Zn II framework of 4‐(pyridin‐4‐ylcarbamoyl)benzoate heterogeneously catalyzed the reaction with an overall yield of 93 % at 70 °C after 48 h (Table S6, entry 2), a yield that is identical to that of catalyst 1 (Table S6, entry 1).…”

Copper(II) and Sodium(I) Complexes based on 3,7‐Diacetyl‐1,3,7‐triaza‐5‐phosphabicyclo[3.3.1]nonane‐5‐oxide: Synthesis, Characterization, and Catalytic Activity

“…[35] In comparison to the few examples found in the literature for the catalytic nitroaldol reaction in aqueous medium by using catalysts based on different transition metals (Table S1), the yields observed in this work are comparable or even better in some cases, taking into consideration the reaction conditions such as temperature, amount of catalyst, and reaction time. [35,36,[67][68][69][70][71][72] Aerobic oxidation of benzyl alcohol…”