Study On Pd(0)-catalyzed Carbonylation Reaction Of Halogenated Aromatics With CO To Synthesize Amides And Esters

Homogeneous palladium-catalyzed carbonylation of carbon monoxide,halogenated aromatics and amines is one of the most common methods for the construction of aromatic amides and their derivatives.the active sites of homogeneous palladium catalysts are distributed at molecular level and the energy transfer processis is not restricted by interphase diffusion-This advantage has made the homogeneous palladium catalyst possess superior efficiency and selectivity in the reactions.However,homogeneous palladium-catalytic process generally requires the participation of expensive steric phosphine ligands.In addition,this kind of catalyst is hard to recycle after used and easy to remain in the target products,which seriously brings a lot of limitations to its practical application.Recently,in response to the development direction of sustainable and green synthesis,heterogeneous palladium catalyst system has become a hot research to activate CO and realize carbonyl insertion reaction for the construction of amides and their derivatives.Herein,this work focus on Pd?0?/SiO₂-catalyzed carbonylation of aryl iodines with CO to synthisize amides and esters under inorganic alkaline environment and elucidates the reaction mechanism.The main conclusions are obtained in this paper:?1?under the temperature of 80°C and atmospheric CO,using the low loading?capacity of 1 wt%?heterogeneous Pd?0?/SiO₂ as the catalyst,the carbonylation reaction of aryl iodines,amines and CO can take place with the deprotonation of inorganic base.26 kinds of aromatic amides with high selectivity and the moderate 11%-99%yields are successfully obtained.The reaction system exhibits good tolerance to various groups of aryl iodines and amines containing electron-donating groups and electron-withdrawing groups,and the introduction of electron-withdrawing groups on aromatic amines is not conducive to the construction of amide compound.Pd?0?/SiO₂ catalyst has excellent catalytic stability in the reaction system,and the decay value of conversion efficiency remains below 9%after 5 cycles;?2?The reaction undergos a single electron transfer mechanism.The basic reaction mechanism is that the thermal electrons of the active center palladium attacks halogenated aromatics and induces the cleavage of carbon-halogen bond.the deprotonation of the base causes the dissociation of hydrogen from the nucleophilic amine and forms the halogenated hydrogen ultimately.The valence state of palladium remained unchanged before and after the cyclic reaction;?3?In the absence of alkali,the catalytic properties of Pd?0?/SiO₂ can be used to realize the conversion of the hydrogen-free tertiary amines on N-center and aryl iodides to aromatic amides under standard reaction conditions.The amides are created through the cleavage of C-N bond of tertiary amines rather than the deprotonation of base.And the dissociation groups on N atoms has formed aldehydes;?4?The Pd?0?/SiO₂-base reaction system can accomplish the synthesis of ester via the carbonylation of aryl iodines and alcohols under moderate temperature and atmospheric pressure.19 kinds of esters are successfully synthesized with the existence of aromatic alcohols,aliphatic alcohols which possess different carbon chains,alicyclic alcohol and aryl iodines.At the same time,phenol can also effectively react with aryl iodine to produce benzene benzoate.The main features of this paper are as follows:?1?With the promotion of inorganic base,heterogeneous Pd?0?/SiO₂-catalyzed selective synthesis of amides and esters from CO and halogenated aromatics was carried out at low temperature,which provides an effective strategy for the construction of C-C,C-N and C-O bonds of the construction of complex structures under mild conditions.In addition,Pd?0?/SiO₂-catalyzed synthesis of amide compounds of aryl iodines and tertiary amines under normal temperature and atmospheric pressure was realized via the cleavage of C-N bond-this reaction mode offers a new idea for the formation of amides rather than the deprotonation.