Chemical Conversion Of Carbon Dioxide By Bifunctional Metal Complex Catalyst

As a major contributor of greenhouse gases,carbon dioxide?CO₂?is also a cheap,available,non-toxic,non-flammable C₁ resource to various chemicals and alternative to fossil fuels.This work is focus on the C-O bond and C-N bond formation for various high value-added chemicals with CO₂ as raw material,and the exploitation of efficient catalysts,which is significant for the protection of the environment and resource utilization.Specific works of this thesis are as follows:A series of quaternary phosphonium bifunctional metal complexes was developed as catalyst for the construction of C-O bond.First,quaternary phosphonium bifunctional metal complexes were utilized as single-component catalysts for the solvent-free and cocatalyst-free cycloaddition between CO₂ and epoxides,yielding cyclic carbonates in high yields and selectivities.Besides,the bifunctional catalysts were workable for various substrates,including terminal and internal epoxides under mild reaction conditions down to atmospheric pressure.After recycling tests,the catalytic performance and structure of Zn-PPBCl could be maintained.The kinetic studies of different metal centres demonstrated the formation activation energies?E_a?for each.Based on the results and reported literatures,an inferred intramolecular cooperative catalytic mechanism was deduced.Then,the quaternary phosphonium bifunctional catalyt Zn-PPBCl could also used for the solvent-free carboxylation cyclization of CO₂and propargylic alcohols in the presence of triethylamine?Et₃N?.Various propargylic alcohols could be effciently converted to corresponding?-alkylidene cyclic carbonates.The possible cooperative catalytic mechanism catalyzed by Zn-PPBCl/Et₃N was also investigated and discussed.The quaternary phosphonium bifunctional metal complex Zn-PPBCl was also used as catalyst for the construction of C-N bond.First,Zn-PPBCl was utilized as a single-component catalyst for the chemical conversion of CO₂ to formamides in the presence of amines and PhSiH₃.Under the optimal condition,the substrate to various primary or second amines could be expanded.The results shows that the reaction conditions and type of hydrogenalkoxysilanes would change the type of products.Under low temperature and high pressure,the formylated product could be obtained using PhSiH₃ as reductant.By increasing the reaction temperature and lowering temperature,the methylated product could be obtained using Ph₂SiH₂ as reductant.Based on these results,the feasible mechanism for the hydrosilylation of CO₂ with amines to produce formamides and methylamines was proposed.Then,the single-component bifunctional catalyt Zn-PPBCl could also be used for the solvent-free cycloaddition reaction of aziridines and CO₂.This bifunctional catalyst was workable for various substrates to yield corresponding oxazolidinones in good yields and regio-selectivities.Furthermore,Zn-PPBCl was utilized as an efficient catalyst for the cycloaddition reaction of CO₂ with electron-withdrawing and electron-donating substituted 2-aminobenzonitriles to produce various quinazoline-2,4?1H,3H?-diones in good yields.Except two-component reactions,Zn-PPBCl also showed excellent catalytic performance in reductive three-component coupling reaction of CO₂,primary amines,and aldehydes to yield unsymmetrically N,N-disubstituted formamides.The scopes for this bifunctional catalyst of primary amines and aldehydes were relatively wide,various aromatic/aliphatic amines and aldehydes could converted to various unsymmetrically N,N-disubstituted formamides in good yields.The proposed mechanism indicated that amine reacted with aldehyde to produce imine in situ,which acted as the real reactant to further react with CO₂ and PhSiH₃,generating the final product unsymmetrically N,N-disubstituted formamide.Based on the carbonyldiiazole,a series of bifunctional metal complexes was developed as single-component catalyst for the solvent-free and cocatalyst-free cycloaddition reaction between CO₂ and epoxides to yield cyclic carbonates in high yields and selectivities.Besides,the bifunctional catalyst Zn-CDI-H was workable for various substrates under mild reaction conditions down to atmospheric pressure,such as terminal,internal epoxides,even the unsaturated substrates and diepoxides.After recycling tests,the catalytic performance and structure of Zn-CDI-H could be maintained.The superior catalytic performance of Zn-CDI-H may due to the unique surface porous structure for adsorption and concentration CO₂.On the basis of these results,a possible cooperative catalytic mechanism was proposed.The cycloaddition reaction of CO₂ and hydroxyl-containing glycidol was also studied.First,the catalytic performance of various simple catalysts such as quaternary ammonium salts,halide salts and alkyl halides for the cycloaddition reaction under high temperature/atmospheric temperature and atmospheric pressure was investigated.The kinetic studies of different catalysts demonstrated the formation activation energies?E_a?for each.Moreover,glycidol was used as catalyst for the cycloaddition reaction between CO₂ and PO in the presence of KI.The results showed that its corresponding cyclic carbonate glycerol carbonate acted as the real hydroxyl donor to catalyzed cycloaddition reaction between CO₂ and PO together with I^-.Based on the above results,a possible cooperative catalytic mechanism involved hydroxyl and I^-was proposed.