Theoretical Study Of Transition Metals Involved Hyperconjugative Aromaticity

Aromaticity,one of the most important concepts in chemistry,has attracted considerable experimentalists and theoreticians due to its fascinating and ever-increasing manifestations in decades.Hyperconjugation,a weak interaction in organic chemistry,can have a strong effect on aromaticity,leading to the concept of hyperconjugative aromaticity,which was first proposed by Mulliken in 1939.However,most studies are limited to the main group chemistry and carbocyclics.Transition metal substituents are essential in organometallic chemistry and heterocycllics generally exist in organic compounds.Therefore,it is of great significance to explore the hyperconjugative aromaticity of transition metal substituents in heterocyclic systems.Here,a systematic study is carried out to investigate the hyperconjugative aromaticity of transition metal substituents in goup 11 and the selectivity of hyperconjugative aromaticity via quantum chemical method.The structure and bonding of the related systems were analyzed in detail.The main contents are summarized as follows:1.The hyperconjugative aromaticity of the metal substituted heterocyclic compounds,tetra-and octa-aurated heteroaryl complexes were studied.The results show these heterocyclic systems can participate in hyperconjugation,first extending the concept of hyperconjugative aromaticity to the transition metal substituted heterocyclic systems.Further studies also show that the transition metal substituents can perform better than the traditional main group substituents on hyperconjugative aromaticity.2.The hyperconjugative aromaticity of transition metal substituents in group 11 were systematically studied in pyrrolium and indolium.The results show that comparison with gold,silver and copper can also participate in the hyperconjugation and result in the aromaticity switch of five membered ring from nonaromaticity to aromaticity.It is found that the silver exhibits the strongest hyperconjugation effect among transition metals in group 11.Moreover,the most aromatic and antiaromatic pyrroliums have been achieved by combining the hyperconjugation with the push-pull effect.3.The regioselectivity of the main group and the transition metal substituents in the hyperconjugation aromaticity is explored.The study shows that the electronegtive substituent is more likely to form hyperconjugation with carbon atoms rather than nitrogen atoms.However,for the electronpositive substitutions,the selectivity of indoliums will be significantly reduced.In addition,the difference in the thermodynamic stability of the isomers with tera-aurated indoliums is caused by the bond dissociation energy in the system rather than aromaticity.The results of theoretical prediction have been experimentally verified in this study.