Heterogeneous catalitic activity of Novel Indium MOFs

Generally, group IIIA metal-based polycarboxylates are less studied, compared with those of transition or rare earth metals. However, In-MOFs have received recently much attention due to their interesting network topologies, which are mainly owing to the variety of coordination modes (6, 7 or 8) in indium MOFs with O- and N-donor ligands. [1]. Some of In-MOFs exhibit an exceptional gas absorption, fluorescent, ion-exchange properties, and can be used as heterogeneous Lewis acid catalysts in various organic transformations. The high relevance of Indium materials in catalytic studies for important organic reactions led to development of indium MOFs. [2-3] Here we report the solvothermal synthesis, structural characterization, topological analysis and catalytic studies of six new indium-based MOFs using 5-(4-carboxy-2-nitrophenoxy)isophtalic acid (H3popha) together with N-donor ancillary ligands (Figure 1). The three indium compounds showing 3D networks are the following: [In8(OH)6(popha)6(H2O)4]·xH2O (1), [In2(popha)2(4,4-bipy)2] (2) and [In3(OH)3(popha)2(4,4'-bipy)2]·xH2O (3). Meanwhile, compounds with a 2D network have a composition [In(popha)(1,10-phen)]·xH2O (4), [In(popha)(1,10-phen)]·xH2O (5) and [In(popha)(2,2'-bipy)]·xH2O (6). The catalytic study performed using indium compounds 1-6 as catalysts in a Lewis acidity promoted organic reaction, allows for establishing a connection between the corresponding MOF network dimensionality and its catalytic behavior.

Indium Based Metal-Organic Frameworks: The Search for a powerful Green Catalyst

The reduction in negative environment impact is a primary goal in the chemical industry. For these reasons several authors, looking for a "green chemistry", highlighted the special interest in using indium for its diverse physical properties and its stability in air.[1] Our interest is focused on indium MOFs constructed with benzene multicarboxylate ligands, which have been found to be useful building blocks in construction of MOF materials. This approach has allowed the assembly of indium based structures with catalytic activity toward nitroaromatics reduction, sulfide oxidation, aldehydes acetalization and aldehydes cyanosilylation.[2-3] In this way, we have synthesized, purified and characterized five new indium based MOFs using 4,4'-hexafluoroisopropylidene-bis-(benzoic acid) (H2hfipbb) as bent organic linker together with N-donor ancillary ligands, which gave rise to materials with the composition [In(OH)(hfipbb)] (1), [In2(hfipbb)3(1,10-phen)2]·2H2O (2), [In2(hfipbb)3(2,2'-bipy)2]·2H2O (3), [In2(hfipbb)3(4,4'-bipy)] (4) and [In4(OH)4(hfipbb)4(4,4'-bipy)] (5). Taking to account the Lewis acidity properties that these compounds could present, 1-5 were tested in the cyanosilylation reaction (CSR) of aldehydes and ketones.

9,9'-Spirobifluorene Based MOFs: Synthesis, Structure, Catalytic Properties

The 9,9'-spirobi[fluorene]-3,3',6,6'-tetracarboxylic acid (H4SBF), a ligand based on the spirobifluorene (SBF) core, was used as a ligand for the synthesis of the MOFs [Co(H2SBF)Phen(H2O)]n (1), and [M(H2SBF)(4,4-Bipy)]n (M = Co, Ni, Cu) (2). The ligand H4SBF is based on the spirobifluorene (SBF) core: the interest in the SBF platform is due to its application as chiral ligand in organic electronics, as solid state laser or in third-order nonlinear optics. The MOFs with H4SBF have been obtained by hydrothermal reaction of H4SBF, the corresponding MCl2 and the base (Phen or 4,4-Bipy) in a molar ratio H4SBF : M2+ : base = 1:1:1. The obtained MOFs are stable in air and thermally stable up to ~400°C. The MOFs 2 (M = Co, Ni, Cu) are isostructural (proved by DRXP data). Only for 1 and 2 (M=Ni) the crystals were obtained apt for crystallographic study. The Ni compound crystallizes in monoclinic system, Cc space group with cell parameters: 40.8251 Å, 12.0031 Å, 11.8383 Å and β = 104.398⁰, vol. 5618.89 Å3. Ni metal center is hexacoordinated in an octahedral environment with five O atoms of two ligands and one N atom from 4,4- Bipy, which means that there is another N atom not coordinated to metal center. The structure of 2 is 2D with interlayer H bonds, which built up a supramolecular 3D net. The Co compound is triclinic, P-1 space group with cell parameters: 10.9775 Å, 12.7231 Å, 14.2381 Å, α = 65.203⁰, β = 87.528⁰, γ = 72.947⁰, vol. 1718.6 Å3. Like Ni compound, Co metal center is hexacoordinated in an octahedral environment with three O atoms of one ligand, two N atoms from Phen and one water coordinated molecule, which builds up a 2D structure. To test the catalytic ability, the obtained MOFs were used to oxidize styrene molecules with tert-butyl hydroperoxide oxidant. Styrene was fully oxidized into its epoxidized product by 1 in CH2Cl2 in 6 h. Under the same conditions, 1 can oxidize the most inert cyclohexane substrate at 60°C with 80.6% substrate conversion.