Two ligand-functionalized Pb(ii) metal–organic frameworks: structures and catalytic performances

Abstract

A microporous Pb(II) metal-organic framework (MOF) [PbL(2)]·2DMF·6H(2)O (1) has been assembled from a N-oxide and amide doubly functionalized ligand HL (= N-(4-carboxyphenyl)isonicotinamide 1-oxide). Complex 1 features a three-dimensional (3D) framework possessing one-dimensional (1D) rhombic channels with dimensions of 13 × 13 Å(2). The 3D framework is built up from 1D PbO(2) chains that link ligands in parallel fashion to construct single-wall channels. When recrystallizing 1 in a DMSO-DMF mixture (3 : 5 v/v), a new coordination polymer, [PbL(2)]·DMF·2H(2)O (2), was obtained. Complex 2 is also a 3D framework containing 1D rectangular channels, but the channel dimensions become reduced in size to 13 × 8 Å(2) due to reorganization of the Pb(ii) coordination environment. The PbO(2) chains in 2 are reformed to link ligands in a double-wall fashion, significantly reducing the channel size. Even though, the guest exchange study indicates that the DMF molecules in 2 could be replaced with benzene molecules when immersing in benzene solvent, showing single-crystal-to-single-crystal (SC-SC) guest exchange in the solid state and leading to a daughter crystal [PbL(2)]·0.5C(6)H(6)·2H(2)O (2'). Desolvated 1 and 2 display preferential adsorption behaviors of water vapour over CO(2) due to the hydrophilic nature of the channels and the strong host-guest interactions. Catalytic tests indicate that desolvated 1 and 2 have size-selective catalytic activity towards the Knoevenagel condensation reaction.

Solvent-Dependent Structural Variation of Zinc(II) Coordination Polymers and Their Catalytic Activity in the Knoevenagel Condensation Reaction

“…[63][64][65][66][67][68][69][70][71][72][73][74][75][76] This condensation is generally catalyzed by bases or Lewis acids and widely studied in homogeneous systems. 90,91 Only a few studies have employed heterogeneous catalysts including metal organic frameworks.…”

“…There are some reports on coordination polymers which are catalysts for this kind of reaction, [63][64][65][66][67][68][69][70][71][72][73][74][75][76] and a comparison with our catalyst 3 is shown in Table 3. The obtained yields in our system are usually higher than for the other reported zinc(II) frameworks in which the reaction of benzaldehyde and malononitrile, after a longer time and at a higher temperature, leads to an overall yield that is lower or identical to ours (Table 3, entries 2,3).…”

“…71 Moreover, when we performed the reaction at room temperature with our catalyst 3, a 97% yield was reached only in 6 h ( Table 3, entry 6), which is a much lower time than those for other 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 reported Cd(II) and Pb(II)-MOFs (Table 3, entries 7 and 8). 73,74 In comparison with other catalysts, ours have the advantages of being rather cheap, easy-to-prepare and highly active at low temperature. Moreover, they are recyclable without appreciable loss of activity.…”

“…49 Recently, we have reported various coordination polymers which are catalytically active for the oxidation of alkanes, alcohols or olefins. [50][51][52][53][54][55][56][57][58][59][60][61] Acidic and basic polymers can exhibit high catalytic activity in condensation reactions like the Pechmann, 62 Knoevenagel, [63][64][65][66][67][68][69][70][71][72][73][74][75][76] and Prins reactions. 77 Coordination polymers can work as catalysts through two different components, viz.…”

Annulation of phenols with methylbutenol over MOFs: The role of catalyst structure and acid strength in producing 2,2-dimethylbenzopyran derivatives

“…Friedländer condensation [38], Knoevenagel condensation [39][40][41][42][43], Huisgen cycloaddition [44], selective oxidation of cycloalkanes [45], and Friedel-Crafts benzylation [46].…”