Performance Study Of Formic Acid Dehydrogenation And CO₂ Hydrogenation Reduction Catalyzed By Pyridylpyrrole Cp*Ir（Ⅲ） Complexes

Carbon dioxide（CO₂）is one of the most widely utilized carbon sources in nature,and it is also the most common greenhouse gas.CO₂fixation and conversion into high value-added products such as formic acid（HCOOH）is one of the important strategies for CO₂ resource utilization and greenhouse effect mitigation,which has important practical needs.CO₂has high thermodynamic stability and inert kinetics in the conversion process.The reaction system of converting CO₂ into HCOOH in aqueous phase through metal complex molecular catalyst is a hot issue concerned by scientists.In addition,the obtained HCOOH has the characteristics of low toxicity,convenient transportation and decomposition at normal temperature and pressure.It is considered to be an excellent hydrogen storage material.Although the thermodynamics of HCOOH dehydrogenation process is feasible,the kinetics is blocked.Therefore,from the perspective of hydrogen energy development and utilization,Transition-metal molecular complexes catalyzing HCOOH dehydrogenation and hydrogenation in aqueous phase has also attracted much attention.This dissertation mainly focuses the performance of Cp*Ir（Ⅲ）complexes based on pyridylpyrrole ligand in catalytic formic acid dehydrogenation and CO₂ hydrogenation,mainly including the following aspects:（1）Design and synthesis of pyridylpyrrole ligands and corresponding complexes.The ligands HL₁,HL₂,HL₄,HL₅ and HL₆ were prepared by Suzuki reaction.The pyridylpyrrole as the skeleton structure containing pyridine ring with?-position substituted by-H,-OCH₃,-NH₂,-OH and-CF₃ groups are synthesized.HL₃ ligand contains pyrrole ring modified-CH₃ at the?（11）?position.The ligands HL₈ and HL₉ for pyridine nitrogen oxidation were prepared by oxidation of HL₇ by m-CBPA.The corresponding chloro iridium complexes 1-Cl to 9-Cl were prepared by the reaction of HL₁ to HL₉ and[Ir Cp*Cl₂]₂.The corresponding aqueous iridium complexes 1-H₂O to 9-H₂O were prepared by the reaction of HL₁to HL₉ and[Ir Cp*（H₂O）₃]SO₄.Binuclear iridium complex 10-Cl was prepared by the reaction of ligand HL₇ with Ir（PPh₃）₃Cl and followed by reacting with[Ir Cp*Cl₂]₂.The designed and synthesized ligands and corresponding complexes were fully characterized by NMR,IR,ESI-MS and electron absorption spectroscopy.HL₈,HL₉,1-Cl,1-H₂O,2-Cl,4-Cl to 10-Cl were characterized by X-ray single crystal diffraction.（2）Study on catalytic performance of pyridylpyrrole Cp*Ir（Ⅲ）complexes for dehydrogenation from formic acid.Using complexes 1-Cl to 9-Cl and 1-H₂O to 9-H₂O as catalysts,the effects of temperature,catalyst concentration,substrate concentration and p H value on the formic acid dehydrogenation performance were investigated under the condition of aqueous solution.The experimental results show that 2-H₂O complex with electron donating group（-OCH₃）modified at?-position of pyridine ring,4-H₂O complex with proton group（-NH₂）and 8-H₂O complex with basic side group（-O^-）and N?N coordination can effectively improve the efficiency of hydrogen dehydrogenation from acid.The Cp*Ir complex 2-H₂O with?-position modified electron donating group（-OCH₃）on the pyridine ring catalyzes the catalytic conversion of formic acid to hydrogen production under the conditions of p H 3.21,90℃,and formic acid concentration of 2 M,with a TOF of 45900 h^-1.The Cp*Ir complex 4-H₂O formed by modifying the protonic group at the?-position of the pyridine ring catalyzed the conversion of formic acid to hydrogen production under the conditions of p H 1.81,90℃,and formic acid concentration of 2 M,with a TOF of 57571 h^-1.The pyrrole ring-modified Cp*Ir complex 8-H₂O with basic side groups and N?N coordination mode catalyzes the conversion of formic acid to hydrogen production under the conditions of p H 3.21,90℃,and formic acid concentration of 2 M.The TOF is reached to 125561 h^-1.The effects of pyridine modification and pyrrole modification on catalytic performance of formic acid dehydrogenation were also investigated.The optimal reaction conditions were obtained.Through intermediate separation and characterization,KIE experiment and the study of relationship between temperature and reaction rate,the reaction mechanism of formic acid dehydrogenation catalyzed by pyridylpyrrole Cp*Ir（Ⅲ）was studied（3）Study on catalytic performance of pyridylpyrrole Cp*Ir（Ⅲ）complex for CO₂ hydrogenation.Using complexes 1-Cl to 9-Cl and 1-H₂O to 9-H₂O as catalysts,the effects of catalyst,temperature,pressure,on CO₂hydrogenation were investigated under aqueous solution conditions,and the catalytic reaction conditions were optimized.The electron-donating group（-OCH₃）was modified at the?-position of the pyridine ring to form a Cp*Ir complex 2-H₂O.The catalytic conversion of CO₂ hydrogenation to formic acid reached 4.5 h^-1 at 25℃and 0.1 MPa.The catalytic conversion TOF of Cp*Ir complex 8-H₂O,which contains basic side groups and forms NN coordination mode,catalyzed CO₂ hydrogenation to formic acid at 120℃,8 MPa reached 348 h^-1.The efficiency of CO₂hydrogenation to formic acid catalyzed by Cp*Ir complex can be greatly improved by increasing temperature and pressure.Through intermediate separation and characterization experiments,the reaction mechanism of pyridylpyrrole Cp*Ir（Ⅲ）CO₂ conversion to HCOOH was studied.Combined with DFT theoretical calculation,the reaction paths of Cp*Ir（Ⅲ）（N^N）Cl and Cp*Ir（Ⅲ）（N^N）（H₂O）were compared,and the thermodynamic process of catalytic reaction was explained in detail.（4）The interconversion of formic acid dehydrogenation and CO₂hydrogenation catalyzed by binuclear complex 10-Cl was also explored.Under the condition of aqueous solution,the effects of different reaction time on the dehydrogenation performance of formic acid were investigated,and the optimal reaction conditions were obtained.