Preparation And Organic Catalytic Performances Of Graphene-based Transition Metal Nanomaterials

Heterogeneous catalysts play a vital role in the chemical and pharmaceutical industries and about 90%of chemical production processes rely on catalytic techniques.The high specific surface area,excellent electron mobility,and excellent thermal stability characteristics of graphene make it a powerful support for the highly reactive metal catalytic active center.Therefore,it is of great significance to promote the application of graphene-based heterogeneous catalysts in the preparation of fine chemicals and pharmaceutical intermediates through the in-depth study of the structure-activity relationship between catalytic efficiency and catalytic center,understanding the catalytic reaction mechanism,and developing various transition metal surface-functionalized graphene-based catalysts.In this paper,a variety of graphene-based transition metal nanomaterials were rationally designed and prepared under the guidance of the target organic reactions.The detailed morphology,structure,and composition of the produced materials were systematically analyzed by diverse characterization methods.Meanwhile,the catalytic properties of the prepared materials were tested,and a series of efficient catalytic systems were established.The active sites and catalytic reaction mechanism of the catalysts were studied.At last,the obtained catalytic systems were applied to explore the synthesis methods of fundamental drugs and their intermediates.（1）Preparation of leaf-like CuO nanosheets supported on rGO and their applications in the homocoupling of terminal alkynes:firstly,CuO nanosheets supported on rGO material（CuO nanosheets/rGO）were prepared by a convenient hydrothermal method.The CuO nanosheets and rGO have formed a composite catalytic center,which makes CuO nanosheets/rGO an economic and highly efficient heterogeneous catalyst in catalyzing the C_sp-C_sp homo-coupling reaction of multifarious terminal alkynes.At the same time,CuO nanosheets/rGO showed excellent recyclability with little activity loss after five cycles,and no obvious change was observed in its morphology and structure.（2）Preparation of copper nanospheres supported on rGO and their applications in the stereoselective syn-boronation of terminal alkynes:while the C≡C bond can be highly activated by copper-based nanomaterials,the catalytic efficiency and selectivity for different organic transformations will be greatly affected due to the formation of catalytic center with different valence states during the preparation and catalytic processes of them.Therefore,the key to overcome this problem lies in the accurate construction of uniform catalytic active centers for Cu-based catalyst.Hence,copper nanospheres supported on rGO（Cu-NPs/rGO）was prepared by a simple glucose reduction method with the assistance of a peristaltic pump.Compared with Cu₂O/rGO and CuO/rGO,Cu-NPs/rGO showed excellent catalytic performance for the stereoselective syn-boronation of terminal alkynes(a TOF value of 13.92 h^-1),which was much higher than other reported Cu-based catalysts.The synergistic mechanism of Cu nanospheres and rGO ensures the good heterogeneous catalytic ability and stereoselectivity of Cu-NPs/rGO for the trans-boric acid esterification of a wide range of terminal alkynes.Meanwhile,the catalytic system for Cu-NPs/rGO possesses excellent cycle stability.The synthesized（E）-β-styrene borate can be used in the one-pot preparation of the vascular drug cinnarizine through Petasis reaction（yield:81%）,which effectively overcomes the shortcomings of the existed preparation methods such as multiple reaction sites and poor selectivity.（3）Preparation of novel corner-cut Cu₂O nanocubes supported on rGO and their applications in the borylation of aryl halides:the oxidative addition efficiency of Cu₂O nanoparticles was low during the catalytic reaction process,which restricted the establishment of high-efficient catalytic systems based on Cu₂O.In this part,the novel corner-cut Cu₂O nanocubes on reduced graphene oxide（Cu₂O/rGO）were prepared using ascorbic acid as a green reducing agent and assisted by a peristaltic pump.Given the different activation energy barriers of C²_sp-I and C²_sp-Br bond in the Miyaura borylation reaction of aryl halides,two different catalytic systems have been established utilizing the synergy mechanism of Cu₂O nanocubes and rGO:iodobenzene borylation in the process of oxidative addition/reduction elimination and bromobenzene borylation in the process of free radical,respectively.The heterogeneous borylation systems catalyzed by Cu₂O/rGO have completed the construction of the C²_sp-B bond for various aryl halides.Furthermore,the obtained borylation products were treated with a one-pot coupling method for the preparation of sartan and other basic pharmaceutical intermediates.（4）Preparation of Cu Fe₂O₄ nanoparticles supported on rGO and their applications in the oxidative cleavage of the C=C bond for alkenes:magnetic Cu Fe₂O₄-based nanomaterials own superior activity in catalytic oxidative coupling reactions by TBHP,but their related research on the catalytic cleavage of sp² hybrid carbon-carbon bond oxidized by TBHP through the heterogeneous process is rare.In this chapter,the solvothermal synthesis of rGO nanomaterials with different Cu Fe₂O₄ loadings（Cu Fe₂O₄/rGO）was designed and synthesized,TBHP was used as a green oxidant to oxidize alkenes and produce varied aldehydes.It is found that20%-Cu Fe₂O₄/rGO material can be used as a cheap and readily available heterogeneous catalyst for the cleavage of C=C double bond with high efficiency.The Cu Fe₂O₄ nanoparticles in the catalyst activated the carbon-carbon double bond and played a synergistic catalytic role with rGO to promote the decomposition of TBHP and the generation of·OOH,thereby realizing the oxidative cleavage of the C=C bond under mild conditions.In this chapter,the established catalytic oxidation system enhanced the application of graphene-based materials in the conversion of styrene derivatives with different substituting groups to produce aromatic aldehyde-based fine chemicals.（5）Preparation of spherical CoNi alloys supported on rGO and their applications in catalytic N-alkylation reactions by borrowing hydrogen for amines and alcohols:the poor selectivity of the traditional method depended on the alkyl halides can be well avoided by the catalytic alkylation reaction through borrowing hydrogen strategy for amines and alcohols.The activation of the inert C³_sp-H bond of the alcoholic hydroxyl is crucial to this reaction.Besides,the high energy barrier in the functionalization of the C³_sp-H bond makes the reaction carried out in harsh conditions.Thus,a direct N-alkylation strategy of amines and alcohols catalyzed by CoNi/rGO material was designed.Three kinds of CoNi/rGO materials with different loadings of spherical CoNi alloy were synthesized by the solvothermal method and acted as the catalyst for the alkylation of amines and alcohols,and their catalytic N-alkylation reaction behavior was studied.By comparison,40%-CoNi/rGO was selected as an efficient catalyst for the N-alkylation reaction of amines with alcohols.CoNi alloy has formed a composite catalytic center with rGO,which highly activated the C³_sp-H bond and promoted the transfer of hydrogen during the reaction process,and finally realized the N-alkylation of different kinds of amines and alcohols via a borrowing hydrogen strategy.At the same time,the established catalytic system was employed in the exploration of new synthesis methods for piperazine-based pharmaceutical intermediates and butenafine.