[Cu(H2btec)(bipy)]∞: a novel metal organic framework (MOF) as heterogeneous catalyst for the oxidation of olefins

Abstract

A new extended metal-organic framework [Cu(H2btec)(bipy)]infinity. (1) (H4btec= 1,2,4,5-benzenetetracarboxylic acid; bipy = 2,2'-bipyridine) has been hydrothermally synthesized. Violet crystals are formed in a monoclinic system with a space group C2/c; a = 10.1810(18) A, b = 14.4360(18) A, c = 12.894(3) A, beta = 112.94(3) degrees. In the title compound 1 each Cu(II) centre has a distorted square planar environment, completed by two N atoms from one bipy ligand and two O atoms belonging to two dihydrogen benzene-1,2,4,5-tetracarboxylate anions (H2btec2-). The {Cu(bipy)}2+ moieties are bridged by H2btec2- anions to form an infinite one-dimensional coordination polymer with a zig-zag chain structure along the c axis. A double-chain structure is formed by hydrogen bonds between adjacent zig-zag chains. There are also pi-pi stacking interactions between the bipy ligands, with an average distance of 3.62 A resulting in a two-dimensional network structure. Compound 1 was tested as a catalyst for the oxidation of cyclohexene and styrene, with tert-butyl hydroperoxide (TBHP) as oxidant. The catalytic activity (24 h and 75 degrees C) found for [Cu(H2btec)(bipy)]infinity shows a high value for the conversion of cyclohexene (64.5%), and a lower one for styrene (23.7%). High turnover frequency (TOF) values for the epoxide products were observed, indicating that the catalyst synthesized in this work, not only has a high activity and selectivity for epoxidation reactions but is also very efficient.

Aerobic Epoxidation of Olefins Catalyzed by the Cobalt‐Based Metal–Organic Framework STA‐12(Co)

“…MOFs usually have high porosity and specific surface areas that make them adequate candidates for catalytic applications both as high-surface-area supports and as intrinsic catalysts. [26,27] MOFs have been used as catalysts for various types of oxidation reactions in the liquid phase, for example, alcohol oxidation, [28] epoxidation, [29][30][31][32] hydrocarbon oxidation, [33][34][35][36] hydroquinone oxidation, [37] the oxidation of organic sulfides, [38] and the oxidation of aromatics. [39] For these oxidation reactions especially, a certain degree of deactivation is frequently observed.…”

Metal-Organic Frameworks as Selective or Chiral Oxidation Catalysts

“…Although a significant difference is observed in the conversion of both reactants (cyclohexene and styrene), a selectivity of approximately 70% toward the epoxide was detected in both cases. In an additional report, the authors proposed a mechanism for the formation of the epoxide and they ascribed the difference in conversion for cyclohexene and styrene to the mechanism involved in the oxidation reaction 88 . Table 4).…”

Metal–organic frameworks as heterogeneous catalysts for oxidation reactions

“…However, one of the major problems of 55 It is interesting to note that TBHP was used in equimolar amounts and, therefore it appears that the copper MOF exhibits a high selectivity for the oxidation from the point of view of the hydroperoxide consumption, minimizing spureous TBHP decomposition. However, the stability of catalyst in terms of leaching and reusability was not reported and this is an issue of large importance, particularly in oxidation reactions.…”