Technical Field
The present disclosure relates to metal organic frameworks comprising zinc (II) ions and second metal ions, such as iron (II) ions, cobalt (II) ions, and copper (II) ions as nodes or clusters and coordinated 1,3,5-benzenetricarboxylic acid struts or linkers between them. Additionally, the present disclosure relates to processes for producing the metal organic frameworks and their application as catalysts in methods for the oxidation of cyclic hydrocarbons, such as toluene, cyclohexane, and methylcyclohexane.
Description of the Related Art
The “background” description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description which may not otherwise qualify as prior art at the time of filing, are neither expressly or impliedly admitted as prior art against the present invention.
Metal organic frameworks (MOFs) are crystalline, highly porous coordination polymers which are comprised of inorganic units (i.e. metals) coordinated to rigid organic fragments. They were built by a node linker approach that was first described by Robson [Hoskins, B. F.; Robson, R. J. Am. Chem. Soc. 1990, 112, 1546.—incorporated herein by reference in its entirety]. This method uses metal ions as nodes and organic ligands as linkers. In this case, a metal ion with a preferred coordination number and geometry combines with divergent ligand molecules to form an extended 1D, 2D or 3D network or networks. The metal linker interactions vary widely and have included ion-ion interactions, ion-dipole, dipole-dipole, hydrogen bonding, anion-π interactions, π-π interactions, as well as van-der Waals interactions [Burrows, A. D.; Chan, C. W.; Chowdhry, M. M.; McGrady, J. E.; Mingos, D. M. P. Chem. Soc. Rev. 1995, 329; and Classens, C. G.; Stoddart, J. F. J. Phys. Org. Chem. 1997, 10, 254.—each incorporated herein by reference in its entirety]. The strength of these interactions has been proven to directly influence the overall stability of the resulting framework [Braga, D. Chem. Comm. 2003, 2751-2754.—incorporated herein by reference in its entirety]. Extended networks can be developed from the basic principles guiding the formation of coordination complexes. FIG. 1 shows a representation of the formation of these coordination networks. Hence, the choice of metal center affects the resulting framework structure because a given metal has preference for a specific geometry and coordination environment.
A second approach to the synthesis of MOFs was described by Yaghi [Eddaoudi, M.; Li, H.; Reineke, T.; Fehr, M.; Kelley, D.; Groy, T. L.; Yaghi, O. M. Topics in Catalysis 1999, 9, 105.; and Eddaoudi, M.; Moler, D. B.; Li, H.; Chen, B.; Reineke, T. M.; O'Keeffe, M.; Yaghi, O. M. Acc. Chem. Res. 2001, 34, 319.—each incorporated herein by reference in its entirety]. This involves the use of multiple organic ligands and linkers and metal ions or clusters (secondary building units, SBUs) as nodes. FIG. 2 shows a schematic illustration of this MOF synthesis and structure. Most often, MOFs are easily synthesized by means of hydrothermal or solvothermal synthesis which involve high temperature self-assembly in a high boiling organic solvent or water in closed vessels [Yaghi, O. M.; O'Keeffe, M.; Ockwig, N. W.; Chae, H. K.; Eddaoudi, M.; Kim, J. M Nature 2003, 423, 705-714.; and Stock, N.; Biswas, S. Chem. Rev., 2012, 112, 933-969.; and Yaghi, O. M.; Li, H. L. J. Am. Chem. Soc., 1995, 117, 10401-10402.; and Lin, W. B.; Wang, Z. Y.; Ma, L. J. Am. Chem. Soc., 1999, 121, 11249-11250.; and Chui, S. S. Y.; Lo, S. M. F.; Charmant, J. P. H.; Orpen, A. G.; Williams, I. D. Science, 1999, 283, 1148-1150.—each incorporated herein by reference in its entirety]. However, these methods typically require long reaction times, from several hours up to several days, depending upon the nature of the ligand, the reaction solvent, reagent concentrations and reaction temperature. They can also be produced using the microwave assisted process which allows the large scale synthesis of MOFs in a few minutes [Feldblyum, J.; Liu, M.; Gidley, D.; Matzger, A. J. Am. Chem. Soc. 2011, 133, 18257-18263.; and Dybtsev, D. N.; Nuzhdin, A. L.; Chun, H.; Bryliakov, K. P.; Talsi, E. P.; Fedin, V. P.; Kim, K. Angew. Chem., Int. Ed., 2006, 45, 916-920.; and Ni, Z.; Masel, R. I.; J. Am. Chem. Soc., 2006, 128, 12394-12395.—each incorporated herein by reference in its entirety].
MOF-5 is one of the first series of MOFs to be reported and fully characterized. It consists of an octahedral secondary building unit (SBU) which is made from Zn4O (CO2)6 as an inorganic unit which is comprised of four ZnO4 tetrahedra with a common vertex and six carboxylate groups. These octahedral SBUs are joined together by benzene linkers [Chalati, T.; Horcajada, P.; Gref, R.; Couvreur, P.; Serre, C. J. Mater. Chem., 2011, 21, 2220-2227.—incorporated herein by reference in its entirety]. These unique units lead to a perfect cubic network whose vertices comprise the SBUs and the edges of which are made up of the benzene linkers. FIG. 3A shows the structure of MOF-5 in an extended 3D cubic framework. This compound was synthesized from Zn(II) and 1,4-benzenedicarboxylic acid (BDC) under organic conditions predetermined to form the SBU in situ. FIG. 3B shows the topology of the MOF structure as a ball-and-stick model. FIG. 3C shows the structure represented by (OZn4)O12 clusters (tetrahedrons) joined by BDC ions (connectors). Since the benzene links and the SBUs appear to be relatively rigid and large entities, the resulting structure has exceptionally high porosity (as indicated by its sorption) and stability [Yaghi, O. M., Sun, Z., Richardson, D. A. & Groy, T. L J. Am. Chem. Soc. 1994, 116, 802-808.—incorporated herein by reference in its entirety].
MOFs have been found to possess unique properties like high surface areas (up to 10400 m2/g) and tunable pores that can be used in various potential applications such as gas storage, catalysis, separation, and drug delivery [Li, H., Eddaoudi, M., O'Keeffe, M. & Yaghi, O. M Nature 1999, 402, 276-279.; and Silva, P.; Valente, A. A.; Rocha, J.; Paz, F. A. A. Cryst. Growth Des., 2010, 10, 2025-2028.; and Wang, Z.; Chen, G.; Ding, K. Chem. Rev., 2009, 109, 322.; and Corma, A.; Garci'a, H.; Xamena, F. X. Chem. Rev., 2010, 23, 1126.; and Li, J. R.; Kuppler, R. J.; Zhou, H. C. Chem. Soc. Rev., 2009, 38, 1477.—each incorporated herein by reference in its entirety]. They have also been found to be candidates for other applications like microelectronics, sensing, optics, micromotors, molecular rotors, and bioreactors [Horcajada, P.; Chalati, T.; Serre, C.; Gillet, B.; Sebrie, C.; Baati, T.; Eubank, J. F.; Heurtaux, D.; Clayette, P.; Kreuz, C.; Chang, J. S.; Hwang, Y. K.; Marsaud, V.; Bories, P. N.; Cynober, L.; Gil, S.; Fe'rey, G.; Couvreur, P.; Gref, R. Nat. Mater., 2010, 9, 172-178.; and Talin, A. A.; Centrone, A.; Ford, A. C.; Foster, M. E.; Stavila, V.; Haney, P.; Kinney, R. A.; Szalai, V.; Gabaly, F. E.; Yoon, H. P.; Le'onard, F.; Allendorf, M. D. Science, 2014, 343, 66.; and Kreno, L. E.; Leong, K.; Farha, O. K.; Allendorf, M.; Van Duyne, R. P.; Hupp, T. Chem. Rev., 2012, 112, 1105.; and Cui, Y.; Yue, Y.; Qian, G.; Chen, B. Chem. Rev., 2012,112, 1126.; and Ikezoe, Y.; Washino, G.; Uemura, T.; Kitagawa, S.; Matsui, H. Nat. Mater., 2012, 11, 1081.; and Comotti, A.; Bracco, S.; Ben, T.; Qiu S.; Sozzani, P. Angew. Chem., Int. Ed., 2014, 53, 6655.—each incorporated herein by reference in its entirety]. Presently, the most highly recognized applications of MOFs, however, have been in the areas of gas storage and separation. The strong interest in this research area stems from the urgent need to develop viable technologies for hydrogen fuel storage for commercial use as well as to control the concentration of CO2 in the atmosphere.
High surface area and the possibility of varied structural modification amongst other desirable physical and chemical properties make it possible for MOFs to efficiently catalyze a broad range of reactions. The MOFs are usually modified by a method that is broadly known as post-synthetic-modification (PSM). PSM makes it possible to incorporate a highly diverse range of different functional groups making it largely free of the restrictions resulting from the synthetic conditions of the MOFs. PSM also allows the introduction of multiple metal ions into a single framework in a combinatorial manner, enabling an effective way to systematically fine tune and optimize MOF properties [Doherty, C. M.; Grenci, G.; Riccoo', R.; Mardel, J. I.; Reboul, J.; Furukawa, S.; Kitagawa, S.; Hill, A. J.; Falcaro, P. Adv. Mater., 2013, 25, 4701.—incorporated herein by reference in its entirety]. The process in which new metal sites are incorporated into a MOF framework is known as transmetallation or post-synthetic metal exchange and the MOFs produced by this method can be described as isostructural MOFs with similar structural frameworks but different metal ions. FIG. 4 illustrates a general scheme for the post-synthetic modification of MOFs. This synthetic method can be used to obtain certain MOFs that cannot be obtained via conventional synthetic methods. Cation exchange also helps to enhance the properties of some MOFs by making it possible to incorporate a more useful metal site thereby improving some of their physical and chemical properties hence giving them more interesting applications. For example, HKUST-1 has a surface area of about 1500 m2/g and it contains Cu2+ but the isostructure can be made by substituting the Cu2+ with other metals. A unique property of transmetallation lies in the fact that new MOFs can be obtained by complete or partial substitution of metal ions within the framework without altering the morphology of the MOFs. FIG. 5 shows a schematic representation for post synthetic metal exchange or transmetallation. This process serves as an alternative, typically milder route for accessing new MOFs when conventional synthesis at high temperature fails [Wang, Z.; Cohen, S Chem. Soc. Rev., 2009, 38, 1315-1329.—incorporated herein by reference in its entirety]. This substitution occurs at the metal nodes, often called the inorganic clusters or secondary building units (SBUs). Although the metal ions are integral parts of the MOFs' structures, they can be replaced either completely or partially within hours or days without necessarily affecting the MOFs' structures [Dinca, M.; Long, J. R. J. Am. Chem. Soc., 2007, 129, 11172-11176.—incorporated herein by reference in its entirety]. Transmetallation changes the properties of the MOFs and also makes them useful for other important applications especially in catalysis. The transmetallated MOFs have multiple properties having separate metal sites that can be utilized for specific catalytic conversions of organic molecules.
The development of efficient new catalysts is still a serious challenge in chemical research. Hence the increasing demand for safer and energy saving reaction routes promotes the need to develop new materials towards the global aim of combating serious environmental challenges that stem from several industrial processes. Hence, catalyst development is an ever growing area of research. Recently, chemists have endorsed MOFs as viable heterogeneous catalysts to channel the course of new and existing chemical reactions to reduce industrial wastes and enable greener chemical processes. This work facilitates better understanding of physical and chemical processes such as surface interactions and facilitates novel concepts and ideas for the next generation of catalysts. The role of heterogeneous catalysts either in chemical or petrochemical industries cannot be overemphasized. They reduce the enormous wastes that are associated with homogeneous catalysts and also reduce cost due to their reusability. These heterogeneous catalysts occur in a different phase from the substrates and predominantly work base on an adsorption mechanism. The heterogeneous catalysts are mostly solids on which liquid or gaseous reaction mixtures are adsorbed. The active site may be either a planar exposed metal surface, a crystal edge with imperfect metal valence or a complicated combination of the two. Thus, not only most of the volume, but also most of the surface of a heterogeneous catalyst may be catalytically inactive. The dependence of catalytic activity on surface area and pore volume makes MOF catalysts a viable area of chemical research. Investigating the nature of the active sites requires technically challenging research. Thus, studies relating to new metal and ligand combinations for catalysis continue.
These highly porous, crystalline MOFs have some of the catalytically important properties of zeolites like uniform cavity and pore sizes as well as medium to large internal surface areas [Wang, L, J.; Deng, H.; Furukawa, H.; Gandara, F.; Cordova, K. E.; Peri, D.; Yaghi, O. M. Inorg. Chem. 2014, 53, 5881-5883.—incorporated herein by reference in its entirety]. Unlike zeolites, vast chemical varieties of MOFs can be synthesized due to the presence of infinite organic linkers. This suggests that the catalytic niche of MOFs is likely to be high value added reactions such as production of specific enantiomers, sensitive molecules, as well as production of fine chemicals, which require specific and tunable catalytic sites [Furukawa, H.; Ko, N.; Go, Y. B.; Aratani, N.; Choi, S. B.; Choi,E.; Yazaydin, A.; Snurr, R. Q.; O'Keeffe, M.; Kim, J.; Yaghi, O. M. Science, 2010, 329, 424.; and Pan, L.; Adams, K. M.; Hernandez, H. E.; Wang, X.; Zheng, C.;Hattori, Y.; Kaneko, K. J. Am. Chem. Soc. 2003,125, 3062.—each incorporated herein by reference in its entirety]. Despite the various interesting and compelling recent developments in MOF catalysis, the area of MOF catalysis is still in an immature phase. Many researchers have likened MOF catalysis to enzyme catalysis, aiming towards the development of catalytic chemistry in the direction of an “artificial enzyme”. Overall, the uniqueness of MOFs over other materials is yet to be fully illustrated since they have been reported to be of use as catalysts in the chemical or petrochemical industries.
Oxidation reactions are among the most important chemical conversions in industries and laboratories. Conversion of abundant and cheap hydrocarbons like toluene, cycloalkanes and methylcyclohexane into more valuable chemicals like aldehydes, ketones and acids stands as a significant process for consideration [Hayashi, H.; Cote, A. P.; Furukawa, H.; O'Keeffe, M.; Yaghi, O. M. Nat. Mater. 2007, 6,501.—incorporated herein by reference in its entirety]. Among these useful transformations, the direct oxidation of toluene to produce benzaldehyde is an attractive process. Toluene oxidation gives a mixture of oxygenated products like benzoic acid, benzyl alcohol, benzaldehyde and cresols. Commercially, benzaldehyde is mainly produced by the chlorination of toluene followed by the hydrolysis process, which generates large amounts of toxic acidic/basic discard solutions, leading to equipment corrosion and environmental pollution. Furthermore, the benzaldehyde produced by this route is not qualified to synthesize some high quality compounds such as perfumes or pharmaceuticals because the product contains chlorine [Friedrich Brihne and Elaine Wright “Benzaldehyde” in Ullmann's Encyclopedia of Industrial Chemistry, 2002, Wiley-VCH, Weinheim.—incorporated herein by reference in its entirety]. Therefore, there is a clear need to develop new materials to improve the selective oxidation of toluene as an alternative route to produce benzaldehyde and consequently benzoic acids.
Alkanes are naturally abundant and cheap carbon containing raw material which serve as attractive substrates for the production of value added organic chemicals (alcohols, ketones, aldehydes and carboxylic acids) [B. Retcher, J. S. Costa, J. Tang, R. Hage, P. Gamez, J. Reedijk, J. Mol. Catal. A. 2008, 286, 1-5.—incorporated herein by reference in its entirety]. Unfortunately, the chemical inertness of these compounds is a considerable limitation towards their vast application for direct syntheses of oxygenated products under relatively mild conditions. However, a proper metal catalyst and an appropriate oxidizing agent, as well as properly controlled reaction conditions, can lead to the development of a cleaner and more efficient chemical industry. Today, over a billion tons of cyclohexanone and cyclohexanol are produced every year and they are mostly used for the synthesis of Nylon-66 and Nylon-6 [M. Musser “Cyclohexanol and Cyclohexanone” in Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim, 2005.—incorporated herein by reference in its entirety].
The structure of HKUST-1 and Zn-HKUST-1 metal organic frameworks has been investigated. Chui and coworkers were the first to synthesize HKUST-1 at the Hong Kong University of Science and Technology. HKUST-1 was discovered to be a highly porous metal coordination polymer [Cu3(BTC)2(H2O)3]n (where BTC is benzene-1,3,5-tricarboxylate) which has interconnected [Cu2(O2CR)4] units (where R is an aromatic ring), C18H12O15Cu3. It creates a 3-dimensional system of channels with a pore size of approximately 1 nm and an accessible porosity of about 40% in the solid. The single crystal structural analysis of HKUST-1 revealed that the polymer framework is composed of dimeric cupric tetracarboxylate building units, with a Cu—Cu inter-nuclear separation of 2.628(2) Å . FIG. 6 shows the crystal structure of the dicopper (II) tetracarboxylate building block containing two axial aqua ligands. The framework was found to be neutral because the twelve carboxylate oxygens from the two BTC ligands bind to four coordination sites for each of the three Cu2+ ions of the formula unit. Hence each Cu atom completes is pseudo-octahedral coordination sphere with the presence of axial aqua ligands opposite to the Cu—Cu dimer. The tetracarboxylate unit provides a structural motif with potential four-fold symmetry, and the trimesic acid provides a three-fold symmetry element. FIG. 7 shows a HKUST-1 secondary building unit (SBU) demonstrating the tbo net topology and the paddlewheel structure. The origin of the nanochannels can be clearly considered to arise from the formation of larger octahedral secondary building units (SBUs). The main SBU in HKUST-1 is the octahedral unit with Cu2 at its 6 vertices and 4 trimesate ions tetrahedrally disposed as “panels” for four of the eight triangular faces of the octahedron. FIG. 8 shows the [Cu3(TMA)2(H2O)3] unit viewed along the cell body diagonal, demonstrating a hexagonal-n shaped window at the intersection of the nanopores. FIG. 9 shows the polymer framework and nanochannels with four-fold symmetry.
The Zn-HKUST-1 that contains Zn2+ ions is analogous to HKUST-1. Analysis of Zn-HKUST-1 by powder X-ray diffraction and gas sorption shows the retention of crystalline structure but negative nitrogen uptake at 77 K due to a dense surface layer that prevents the passage of small molecular species into the crystal framework [Bhunia, M. K, Hughes, J. T. Fettinger, J. C. and Navrotsky, A. Langmuir 2013, 29, 8140-8145.—incorporated herein by reference in its entirety]. The prevalence of zinc paddlewheels in a variety of MOFs, such as the previously discussed HKUST-1 suggests that Zn I a promising metal with which an isostructural analog to Cu-HKUST-1 can be constructed.
The application of metal organic frameworks has been investigated. Over the past decades, transition metal complexes comprising mainly phosphine ligands, salen or salophen ligands, pincer ligands and N-heterocyclic carbenes (NHCs) have had a remarkable impact on catalysis. Examples include the Nobel prize winning Noyori asymmetric hydrogenation, Sharpless oxidations (Sharpless epoxidation, Sharpless asymmetric dihydroxylation, and Sharpless oxyamination) as well as Jacobsen epoxidation [Noyori, R Adv. Synth. Catul 2003, 345, 12, 15-41.; and Katsuki, T.; Sharpless, K. B J Am. Chem. Soc., 1980, 102, 5974-5976.; and Jacobsen, E. N.; Marko, T.; Mungall, W. S.; Schroeder, G.; Sharpless, K. B. J. Am. Chem. Soc., 1988, 110 1968-1970.; and Sharpless, K. B; Patrick, D. W.; Truesdale, L. K.; Biller, S. A. J. Am. Chem. Soc., 1975, 97, 2305 2307.; and Zhang, W.; Loebach, J. L.; Wilson, S. R.; Jacobsen, E. N. J. Am. Chem. Soc., 1990, 112, 7, 2801-2803.—each incorporated herein by reference in its entirety]. Most of these metal complexes have only been successful as homogeneous catalysts which have significant disadvantages like the difficulty of product separation, poor reusability and toxicity. Relatively insoluble and stable materials like zeolites, metals and metal oxides are widely used as heterogeneous catalyst on the industrial scale. Notable conversions like the Harber-Bosch, Contact process, Ostwald process, steam reforming, petrochemical reactions Ziegler Natta polymerization make use of these insoluble materials. In terms of easy post reaction separation, these materials have largely been successful. However, there is still an urgent need for the development of new materials that will be more energy efficient, more tunable, and more environmentally friendly.
MOFs have shown great catalytic prospects for a wide range of reactions due to the diversity in their structures, low toxicity, reusability and cost effectiveness. In fact MOFs are among the best candidates in bridging the gap between homogeneous and heterogeneous catalysis. The metals in the MOF structure often act as Lewis acids especially when the frameworks are activated by removing the coordinated labile solvent molecules or counter ions [Han, J. W.; Hill, C. L.; J. Am. Chem. Soc., 2007, 129, 15094.—incorporated herein by reference in its entirety]. Fujita, et al. first reported the catalytic activity of a 2D Cd(II) based MOF for the cyanosilylation of aldehydes. Thy obtained the unsaturated metal cluster by removing two water molecules from the octahedral structure of [Cd(4,4′-bpy)2(H2O)2].(NO3)2.4H2O [Fujita, M.; Kwon, Y. J.; Washizu, S.; Ogura, K. J. Am. Chem. Soc. 1994, 116, 1151-1152.—incorporated herein by reference in its entirety]. Fe(BTC) has also been used as a heterogeneous catalyst for the selective methylation of primary aromatic amines using dimethyl carbonate, efficient oxidation of benzylic compounds using t-butyl-hydroperoxide as oxidizing agent, and oxidation of thiols to disulfides [Dhakshinamoorthy, A.; Alvaro, M.; Garcia, H. Appl. Catal. A: General 2010, 378, 19-25.; and Dhakshinamoorthy, A.; Alvaro, M.; Garcia, H. J. Catal. 2009, 267, 1-4.; and Dhakshinamoorthy, A.; Alvaro, M.; Garcia, H. Chem. Commun., 2010, 46, 6476-6478.—each incorporated herein by reference in its entirety]. Seo, et al. first reported asymmetric catalysis using a homochiral MOF, [Zn(μ3-O)(1-H)6.2H3O.12H2O] for transesterification reactions. It was also the first MOF demonstrating that the organic linker embedded into a pore can catalyze an asymmetric reaction [Seo, J. S.; Whang, D.; Lee, H.; Jun, S. I.; Oh, J.; Jeon, Y. J.; Kim, K. Nature, 2000, 404, 982-986.—incorporated herein by reference in its entirety]. Lin, et al. also reported the activity of a homochiral non-interpenetrating MOF which was constructed in finite 1-dimensional [Cd(μ-Cl)2]n zigzag chains with axial bipyridine bridging ligands containing orthogonal secondary functional groups [Wu, C.; Hu, A.; Zhang, L.; Lin, W. J. Am. Chem. Soc., 2005, 127, 8940-8941.—incorporated herein by reference in its entirety]. The chiral secondary functional groups were used to generate a heterogeneous asymmetric catalyst for the addition of diethyl zinc to aromatic aldehydes to afford chiral secondary alcohols at up to 93% enantiomeric excess (ee).
More specifically, the catalytic activity of HKUST-1 has been investigated. HKUST-1 has been particularly well recognized for its high catalytic activity especially when the axial aqua ligands are removed via activation. FIG. 10 illustrates schematically the activation of HKUST-1. Activation gives unsaturated metal sites without affecting the rigid framework of the MOF [Schlichte, K.; Kratzke, T.; Kaskel, S.; Microporous and Mesoporous Materials. 2004, 73: 81-85.; and Lien T. L. Nguyen, Tung T. Nguyen, Khoa D. Nguyen, Nam T. S. Phan Applied Catalysis A: General, 2012, 425, 44-52.—each incorporated herein by reference in its entirety]. Schlichte, et al. first reported the catalytic activity of HKUST-1 when they used the HKUST-1 MOF for the trimethylcyanosilation of benzaldehyde. The open framework of this MOF was activated by removing the two water molecules from axial positions in the octahedral framework. The activated MOF afforded up to 57% conversion of benzaldehyde reaching a selectivity of 89% at 313 K. Nguyen, et al. studied the activity of HKUST-1 for the aza-michael reaction in which amines were reacted with α,β-unsaturated carbonyl groups to prepare β-amino carbonyl compounds and their derivatives. They achieved excellent conversions up to 100% under relatively mild conditions in the presence of 5 mol % activated catalyst. Fourier transform infrared spectroscopy (FT-IR) and powder X-ray diffraction (PXRD) analysis revealed that the catalyst could be reused several times without a significant reduction in its catalytic potency. Atomic absorption spectroscopy showed that the reaction was not influenced by homogeneous catalysis resulting from leached active species.
Using the same material, Phan, et al. was able to react phenols and aryl iodides to form diaryl ethers in an Ullman-type coupling reaction. The heterogeneous reaction leads to high conversion using 5 mol % catalyst in the presence of MeONa as a base. The used catalyst was facilely recovered from the reaction mixture using simple filtration and could be reused without significant degradation [Nam T. S. Phan, Tung T. Nguyen, Chi V. Nguyen, Thao T. Nguyen Applied Catalysis A: General., 2013, 457, 69-77.—incorporated herein by reference in its entirety]. Phan, et al. also reported the highly efficient activity of HKUST-1 for the C-arylation of acetylacetone in the presence of aryl iodides to obtain aryl ketones as major products. HKUST-1 was confirmed to be a true heterogeneous catalyst as there was no effect of homogeneous catalysis of active species leaching into the reaction mixture [Nam T. S. Phan, Tung T. Nguyen, Phuong Ho, and Khoa D. Nguyen ChemCatChem. 2013, 5, 1822-1831.—incorporated herein by reference in its entirety]. Dang, et al. studied the catalytic activity of HKUST-1 for the synthesis of propargylamine via direct oxidative C—C coupling reaction using C—H functionalization between phenylacetylene and N,N-dimethylaniline to give N-methyl-N-(3-phenylprop-2-ynyl)benzenamine as the principal product [Giao H. Dang, Duy T. Nguyen, Dung T. Le, Thanh Truong, Nam T. S. Phan Journal of Molecular Catalysis A, 2014, 300, 306.—incorporated herein by reference in its entirety]. The copper catalyzed reaction afforded 96% conversion after 180 minutes at 120° C. in the presence of 5 mol % copper-based catalyst. The used catalyst was recovered from the reaction medium by filtration and reused for the coupling reaction. Similarly, HKUST-1 has been used as a catalyst for the direct oxidative amination of sp2 C—H bonds. The reaction involves the use of N-methylmorpholine oxide (NMO) as oxidizing agent in the presence of primary or secondary amine as coupling pairs with DMF as solvent at 90-100° C. [Nga T. T. Tran, Quan H. Tran, Thanh T. Journal of Catalysis, 2014, 320, 9-15.—incorporated herein by reference in its entirety].
In view of the forgoing, one object of the present disclosure is to provide relatively cheap and environmentally friendly metal organic framework catalysts designed towards laboratory and industrial scale catalytic applications as opposed to uses in gas storage and carbon capture. Metal organic framework catalysts provide great potential for new and existing chemical reactions for shortest route organic conversions that reduce industrial wastes and enable greener chemical processes through their high tunability, high surface area, stability, and reusability. Specifically, this disclosure is focused on isostructural HKUST-1 metal organic frameworks comprising zinc (II) metal ions and second metal ions, such as iron (II) ions, cobalt (II) ions, and copper (II) ions linked by 1,3,5-benzentricarboxylic acid to form a porous coordination network as polyhedral crystals. This disclosure provides the transmetallation preparation of these metal organic frameworks by post-synthetic metallic exchange of the solvothermally synthesized Zn-HKUST-1 metal organic framework. An additional aspect of the present disclosure is application of these metal organic frameworks as catalysts in methods for the liquid phase oxidation of cyclic hydrocarbons, such as, toluene, cyclohexane, and methylcyclohexane. It is envisioned that the metal organic frameworks of the present disclosure will exhibit strong activity in terms of conversion of the cyclic hydrocarbon, selectivity for a desired oxidized cyclic hydrocarbon product, and reusability. Overall, the metal organic frameworks are envisaged to exhibit strong potential utility as catalysts that aid the increasing demand for safer and energy saving reaction routes that additionally reduce and minimize the adverse environmental impact of industrial wastes.