Applications Of Copper-based Metal-organic Frameworks In Organic Reactions

Homogeneous transition metal catalysts have been widely applied in the synthesis of organic fine chemicals, however, the metal ions residual in the products made it very difficult to purify and separate. It is very important in theory and practice to research highly efficient heterogeneous transition metal catalysts. Metal-organic frameworks(MOFs) have received much attention as catalytic materials due to their unique features, including porous structure, huge specific surface area and the high density of open metal sites in the framework, which may supply a new stretagy to search highly efficient heterogeneous organic catalytic systems.In this thesis, the structure features and preparation methods of MOFs as well as their applications in the fields of heterogeneous catalysis were reviewed. Three highly porous MOFs, denoted as Cu-BTC, Cu-TDPAT and pcu-MOF, respectively, were fabricated by solvothermal method, meanwhile their physicochemical properties had been characterized by using the thermogravimetric analysis(TGA), powder X-ray diffraction(XRD), scanning electronic microscopy(SEM), N2 adsorption-desorption, and etc. All three MOFs were used directly or supported noble metal or encapsulated metalloporphyrin to Ullmann and Goldberg C-N coupling reaction, N-S oxidation coupling reaction, amines oxidation coupling reaction, Suzuki and Heck coupling reaction and oxidation of catechol. The main results obtained in this thesis are as follows:(1) A detailed investigation of Ullmann and Goldberg type C-N coupling reactions was carried out using a porous metal-organic framework, Cu-TDPAT, as an efficient heterogeneous catalyst, which was constructed from paddle-wheel type dinuclear copper cluster and organic ligand. It has been demonstrated that Cu-TDPAT can improve the N-arylation reaction of a wide variety of amines and amides with iodobenzene or bromobenzene efficiently. The experimental results proved that Cu-TDPAT was stable to the conditions of Ullmann and Goldberg type coupling reaction, and the open copper sites on the axis of paddle-wheel SBUs within MOF were responsible for the promotion of the C-N coupling reaction. A possible mechanism for the N-arylation is that the halobenzene molecule interacts with copper ion firstly and forms a ?-complex, then the amine species attack the halobenzene activated by copper, giving the coupling product.(2) We have shown for the first time that copper-based MOF is an efficient heterogeneous catalyst for the oxidative coupling of amines and disulfides or thiols. This protocol provides a novel and direct synthesis of N-sulfenylimines in good yields without the formation of N-sulfinyl- and N-sulfonylimines. Based on the control experiments and the characterization data, a plausible two steps mechanism was proposed, which involved the imine formation by amine oxidation and the N-S coupling reaction. The electron paramagnetic resonance(EPR) spectra showed that part of the Cu(II) ions on the MOF framework were reduced to Cu(I) species by the disulfide, which can be oxidized into Cu(II) by O2 oxidation at the end of the reaction without affecting heterogeneous nature of the MOF catalyst.(3) On the basis of the N-S coupling reaction, the pcu-MOF was applied as a heterogeneous catalyst in oxidative coupling reaction of benzylamine derivatives to generate N-imide with high selectivity, without the formation of over oxidation by-product, benzene nitrile. The post-processing of reaction is convenient, in which the catalyst can be removed by simple filtration.(4) Two porphyrin@MOF type catalysts, CuTNPP@MOF and MnTNPP@MOF, have been synthesized through solvothermal method in “one-pot”, and their catalytic abilities were evaluated by using the oxidation of 3, 5-di-tert-butylcatechol(DTBC) as a probe reaction. It was found that CuTNPP and pcu-MOF were both efficient for the DTBC oxidation reaction, nevertheless MnTNPP was catalytically inactive, resulting the discrepancy between the catalytic activities of CuTNPP@MOF and MnTNPP@MOF. The copper centre of the encapsulated CuTNPP molecule and the open copper sites within the MOF are the active sites in catechol oxidation. The contribution of the nicotinoyl groups on the periphery of porphyrin ring to the oxidation reaction was undetectable.(5) The applications of Cu-TDPAT supported palladium catalyst in Suzuki and Heck coupling reaction were preliminarily studied.