Design, Synthesis Of Heterogenous Porphyrinic Catalysts And Their Catalytic Performance

Green Chemistry and Sustainable Technology has been widely considered as the forefront of the current international chemistry field. It mainly focuses on the elimination of chemical pollution from chemical industry via chemical principle. Of these, heterogeneous catalysis has brought hope for the future in order to meet the demand for green chemistry. It usually has significant advantages, such as easy separation, recovery, recycling, and post-processing, which makes heterogeneous catalysis become the key factor in research, development and practical application of catalytic field. Therefore, heterogeneous catalysis shows a good prospect. Porphyrin and its derivatives, as a class of important biomimetic catalysts, can effectively simulate the cytochrome(P450) function, thus showing a good catalytic performance. However, it suffers several drawbacks when porphyrins using as homogeneous catalysts, for instance, poor stability, rapid deactivation and recycling issues, which limits the further development of porphyrin based biomimetic catalysis.In recent years, frame materials are very competitive in the application of heterogeneous catalysis mainly due to their good controllability, strong design ability and stable structure. Therefore, preparation of porphyrinic frame material, not only enhances the catalytic activity via high-density active sites, but also builds a "confinement effect" on substrate through the channel of frame material. In addition, with the characterization and analysis tools of framework materials, the reaction processes catalyzed by porphyrin framework can be systematically researched, which brings important theoretical significance and application value.In this thesis, a series of metal organic framework and covalent organic framework catalysts based on porphyrin catalytically active sites(including covalent bond linked polymer with periodically arranged unit) have been synthesized. Their catalytic application on fine chemical synthesis, such as catalytic activity and selectivity of unsaturated olefin epoxidation and benzyl amine coupling, has been systematically studied. In addition, we use density functional theory(DFT) of quantum chemistry to optimize structural geometry and single point energy for preparation of porphyrin based catalyst and catalytic processes, in order to achieve the purpose of theory and practice mutual authentication.The main contents and results of this study are listed as follows:1) Metal-organic frameworks(MOFs) have emerged as a type of crystalline porous materials which combine highly desirable properties, such as uniform micropores, high surface areas, and size-controlled channel, making them ideal candidates for nanoscopic cage to encapsulate various functional guests. In this work, a sodalite zeolite-type ZIF-8(zeolitic imidazolate frameworks, Zn(MeIM)2, MeIM=2-methylimidazolate) is selected as the support. Synthetic manganese-porphyrin has been selected as an effectively active site to mimic enzymes. Afterwards, we strategically design encapsulated porphyrinic MOF catalyst, henceforth denoted as Mn-TAPP@ZIF-8(manganese meso-Tetrakis(4-aminophenyl)porphyrin, namely Mn-TAPP). In particular, this novel heterogeneous catalyst, denoted as Mn-TAPP@ZIF-8, shows an enhanced catalytic efficiency no matter for conversion or selectivity, compared to the homogeneous Mn-TAPP. This confirms that Mn-TAPP@ZIF-8 can be used as olefin epoxidation heterogeneous catalyst. On the other hand, this work studied the host-guest interaction between Mn-TAPP and ZIF-8, and then confirmed the synergistic interplay. At the atomic level, the amino substituent on Mn-TAPP coupled with the C-H on the 2-methylimidazolate(MeIM) constitutes a weak hydrogen bond as the host-guest interaction(Por-N…H-MeIM). This resulting satellite peak with a higher intensity than Mn2p3/2 region, can be attributed to the manganese species at high valence state from catalyst, which is caused by a weak hydrogen bond. Mn-TAPP@ZIF-8 has extensive use value in olefin epoxidation. Especially, it shows a good catalytic performance for various different substrate. Mn-TAPP@ZIF-8 has obvious heterogeneous nature and can be reused for three cycles without significant drop in its catalytic activity, as well as selectivity.2) Two metalloporphyrinic metal-organic frameworks(Fe-MMPF and Ni-MMPF) have been successfully constructed by tetrakis(4-carboxyphenyl) porphyrin(H4TCPP) and manganese tetrakis(4-carboxyphenyl) porphyrin(Mn-TCPP) as a bridging ligand and Fe or Ni ions with a stable 3D framework in this chapter. Their crystal structures are determined by X-ray crystallography. For Fe-MMPF, a bent trinuclear iron cluster has been reported, which is not presented in existing MOF structures. For Ni-MMPF, the binuclear Ni motifs are interconnected through the carboxylate bridges to form a rare infinite one dimensional(1D) nanosized ribbon chain. Each Ni-TCPP ligand coordinates with eight Ni atoms of four neighbouring Ni chains to propagate into an overall 3D framework structure. According to their structural features, we use two different systems to evaluate their catalytic performance. 1) For Fe-MMPF/H2O2/NaHCO3 system, Fe-MMPF exhibits high catalytic activity in which cyclohexene could be almost fully oxidized into the epoxide product with 99% selectivity. As the catalytic results shown, NaHCO3 is a highly efficient co-catalyst in this reaction. According to a theoretical study on catalytic mechanism, we suggest a posited catalytic cycle about the O atom transformation: HCO4- as a new oxidant instead of H2O2 provides the O atom, then porMnV=O is formed via the activation of HCO4- and last the nucleophilic attack of olefin substrate at the electrophilic oxygen of por MnV=O happens. The nature of the novel bridging bent trinuclear iron cluster works as electron-withdrawing groups on Mn-TCPP. Thus, the catalytic ability may be greatly enhanced due to its electronic environment. Therefore, we propose a new concept, called “catalysis-promoted charge transfer” according such a pheromone. 2) For Ni-MMPF/TBHP catalytic system, the effect of different electron-donating and withdrawing groups on epoxidation of conjugated olefins has been confirmed based on the catalytic results. There is a relationship between the epoxidation yield and steric hindrance of olefin substrate. On the other hand, a higher electron density on double bond usually increases the nucleophilicity of conjugated olefins towards electrophilic oxygenating intermediates. Moreover, Ni-MMPF can retain its structural integrity and can be recycled for five cycles with no significant drop in its catalytic activity. The conversion is no less than 90% and the selectivity is no less than 98%.3) A porphyrin with hydrazide group(Mn-HTCPP) has been employed as building block, with a hydrazone linkage or linked by the squraraine linkage. We successfully synthesize a class of solid catalysts on epoxidation reaction with novel structure via condensation reaction. Pore structure of the two frameworks are mainly based on stacked hole and they are difficult to dissolve in polar and non-polar organic solvents. For these two catalysts, we exame their performance on epoxidation. The results show that the catalyst Mn-CPF-1 shows a superior performance, indicating the combination of Mn-HTCPP and phthalaldehyde favors to enhance the catalytic ability of manganese porphyrin. When Mn-CPF-1 is used as the catalyst, we examine its performance on the cyclic olefin and chain olefins. The catalyst recycling experiments show that Mn-CPF-1 has a good recyclability and high stability. Of further importance, a detailed XPS study evidences that Mn-CPF-1 owns a more desirable electronic environment than Mn-CPF-2, with a more pronounced redox potential, and therefore has a more efficient catalytic properties of active centers.4) Manganese meso-Tetra(4-nitrophenyl)porphyrin(Mn-TNPP) with four nitro groups at periphery has been employed as building moieties to condense with p-phenylenediamine and benzidine into extended π materials, respectively. Two covalent metalloporphyinic polymers(CMPs) linked by azo(-N=N-) are denoted as azo-CMP-1 and azo-CMP-2. azo-CMP-1 shows a superior catalytic performance. SEM images show that azo-CMP-1 is composed of agglomerated plate-shaped particles, which not only relates with their skeleton but also facilitates the epoxidation reaction. Additionally, azo-CMP series exhibits an amphipathic property, facilitating the diffusion of reactant into channels of azo-CMPs, release of product and preventing the contact with tertiary butanol. Furthermore, in order to gain insight into the epoxidation mechanism, XPS study confirms the effect of organic framework on catalytic active sites: electron is highly dispersed on conjugated organic framework for azo-CMP-1, compared to either azo-CMP-2 or homogenous sites. Therefore, there is a catalysis-promoted electronic environment around the Mn(III) active sites. The catalyst recycling experiments show that azo-CMP-1 has a good recyclability and high stability.5) A photoactive donor-acceptor(D-A) polymer with an improved porosity has been successfully synthesized by connecting porphyrin and melem(2,5,8-triamino-tri-s-triazine) via azo bond in this chapter. Therefore, hole oxidative process, photo-induced electron transfer and energy transfer are established as a “three-in-one photocatalytic system”. On the other hand, the large surface area minimizes the diffusion resistance for mass transport. The DFT, the steady and time-resolved PL spectroscopy show that purple PMP has the ability to absorb light over the visible spectrum. Its structure benefits the spatial charge separation involved in the simultaneous reactions of photogenerated electron-hole pairs. Thus, the electron transfer process is enhanced. From the EPR and UV-Vis results, PMP exhibits greater intensity in the EPR signal than TNPP, thus PMP generated more 1O2 via energy transfer of the triplet electrons. PMP shows excellent performance and recyclability as recyclable heterogeneous metal-free photocatalysts, due to a dual-enhanced catalytically favored process.