Research On Reductive Carboxylation Of Unsaturated Hydrocarbons With CO₂ Catalyzed By Zirconium/Titanium

As is known to all,Carbon dioxide is a kind of greenhouse gas.Because more and more CO₂ is emitted into atmosphere in recent years,the greenhouse effect becomes increasingly severe.In order to protect our living environment,many research institutions in the world are making efforts to capture and fix CO₂ via physical or chemical methods.Carbon dioxide has become an attractive C1 source in organic chemistry due to its abundance,economy and recyclability.However,carbon dioxide molecule is very thermodynamically and kinetically stable.In order to achieve the chemical conversion of carbon dioxide,One of strategies is to prepare high nucleophilic reagents which could proceed nucleophilic addition to carbon dioxide.In recent years,late-transition metals,such as rhodium,palladium,copper,gold and silver,are developed to mediate or catalyze carboxylation with carbon dioxide.Early-transition metals are studied scarely.Organotitaniums and organozirconiums are easily prepared and used without isolation,which served as important synthons for synthesis of heterocycles.Nucleophilic carbon centers in their structures could be utilized in the CO₂ chemistry.In this thesis,with the former transition metals titanium or zirconium as catalyst and economic unsaturated hydrocarbons as raw materials,in the presence of Grignard reagents,high nucleophilic carbon centers are prepared in situ,which react with carbon dioxide to afford a series of carboxylic acids.The main contents are as follows:Hydrocarboxylation of mono-substituted olefins was studied: in the presence of Grignard reagent,high nucleophilic organomagnesium reagents,which is generated in situ through insertion of olefins to Ti-H and transmetalation,proceed nucleophilic addition to carbon dioxide to give a serie of ?-aryl substituted carboxylic acids.This method has four main advantages: Firstly,it uses stable,easily available and inexpensive Cp2 Ti Cl2 as catalyst.Secondly,Grignard reagents are commercially available and they are cheaper than organoaluminum and organozinc reagents.In addition,they are non-flammable in air and more convenient to use.Thirdly,reaction substrates ? alkenes are readily available and the reaction is mild and efficient.Fourth,the reaction is not only suitable for aryl olefins,but also suitable for alkyl olefins.Futhermore,Hydrocarboxylation of alkynes was studied: in the presence of Grignard reagents,high nucleophilic alkenylmagnesium reagents,which are generated in situ through insertion of triple bond to Ti-H and transmetalation,proceed nucleophilic addition to carbon dioxide to give a serie of ?,?-unsaturated carboxylic acids.For unsymmetrical disubstituted alkynes,the reactions proceed smoothly with good regioselectivity.Ethylcarboxylation of alkenes was also studied.catalyzed by Cp2 Zr Cl2,organomagnesium reagents formed in situ,which subsequently react with CO₂ to afford a series of ?-aryl substituted carboxylic acids and ?-ethyl substituted alknoic acids.This method introduces a carboxyl group and an ethyl group at the same time,building two carbon-carbon bonds.Ethylcarboxylation of alkenes is scarcely reported.