A theoretical study on the metal cation-π complexes of Zn²⁺ and Cd²⁺ with benzene and cyclohexene

Abstract

Transition metal cation-π complexes of Zn²⁺ and Cd²⁺ with benzene and cyclohexene have been studied with density functional B3PW91 method. Natural bond orbital (NBO) analyses on the direct cation-π complexes (with direct π-ion contact) indicate that the interaction between the π orbital of the π systems and the empty valance s orbital of the cation (π_PI → s _M²⁺ interactions) dominates the cation-π interactions. Energetical results indicate that formation of metal cation-π complexes in the gas phase is always energetically favourable and these complexes can thus be prepared and observed in experiments in the gas phase. However, in aqueous solution the desolvation penalty of Zn²⁺ and Cd²⁺ is so high that it is energetically unfavourable to form metal cation-π complexes from hydrated Zn²⁺ and Cd²⁺ at both 0 K and room temperature. It would thus be predicted that metal cation-π complexes of Zn²⁺ and Cd²⁺ are not likely to be observed in aqueous solution.

Keywords:

• metal cation-π complex
• DFT
• benzene
• cyclohexene

Acknowledgements

This work was supported by the National Natural Science Foundation of China (20433020, 20573023, 20573024, 20673024), the National Basic Research Program of China (2006CB202502), and Shanghai Science and Technology Committee (06JC14009).