Theoretical Study On Au Induced Hyperconjugative Aromaticity And [1,5]-shift Reaction Mechanism

As a developing and expanding subject,aromaticity occupies an important role in the fields of chemistry.Aromaticity could stabilize the transition states and intermediates and promote reactions.After introducing hyperconjugation into the aromatics,the scope of substituents which affords the hyperconjugation to induce aromaticity has expanded from the main group to transition metals.However,the influence of the oxidation state of the metal center and the maximum of sp3-hybrid atoms with hyperconjugation in aromatic rings remains unclear.On the other hand,The applications of hyperconjugative aromaticity to the reaction mechanism study are needed further inverstigation.Herein,through theoretical computations,we measure the aromaticity of a series of designed Au(Ⅲ)-substituted indoliums and hexa/octa/deca substituted hetero five-membered rings(5MR)and investigate the nature behind the aromaticity.For substituted isoindenes,indenes and their derivatives which contain an anti-aromatic benzene ring,the mechanism of the conversion between substituted isoindenes and indenes by[1,5]-shift reaction and the factors to influence the energy barriers and stability of intermediates and reactants are explored in detail.Our researches could pave the way to inspire new ideas for synthesizing new aromatic organometallic compounds and provide new direction to regulate[1,5]-shift reaction.The research results are as follows:(1)By designing a series of Au(Ⅲ)-substituted indoliums which contain different ligands and analysing their aromaticity changes,the results show that,compared with Au(Ⅰ)-substituted indoliums,the influence of ligands in Au(Ⅲ)-substituted indoliums is more pronounced.The aromaticity of the 5MR of indoliums could disappear and recover by tuning the electron-donating ability of Au(Ⅲ)-substituents.In addition,the configuration of Au(Ⅲ)substituents is another factor to affect the aromaticity of 5MR.The aromaticity of 5MR is increased when the configuration of Au(Ⅲ)substituents changed from the trans to the cis.(2)By measuring the aromaticity of 5MR in a series of tetra/hexa-substituted indoliums and octa/deca-substituted pyrroliums,the results show that the hetero-5MR with multi-hyperconjugation could also be aromatic.When the electron-donating ability of substituent is strong enough,the hyperconjugation effect of substitutents could make the 5MR satisfy the 6π electronic system.Meanwhile,the increased number of sp3-hybrid atoms would lead to the increase of steric hindrance in the ring.While the strong non-covalent interaction between transition metal,which is also called metallophilic interaction,is key factor to stabilize the compounds and maintain the planar structure without the loss of substitutents.(3)By investigating the mechanism of[1,5]-shift reaction under the conversion between substituted isoindenes and indenes which have an antiaromatic or resonance restricted benzene ring,the results show that the BDE energy of migration substitutents(C-R bond)and the deformatiom of transition states are significantly influence the energy barrier.The aromaticity for transition state could further reduce the energy barrier.On the other hand,the resonance structure variation of the benzene ring plays a great role in stabilizing the intermediates and reactants.