Modeling ion-π interactions of transition metal complexes

Abstract

Interactions of π-systems with ions are very important for many chemical and biological systems. In this work we show how transition metal coordination strengthens cation-π interactions, and how it makes anion-π interactions of some systems possible. The calculations showed that cation-π interactions between ferrocene and alkali metal ions are stronger than cation-π interactions of benzene. The strongest cation-π interaction is between ferrocene and Li+, with interaction energy of -44.0 kcal/mol, while benzene-Li+ interaction has the energy of -36.1 kcal/mol. Cation-π interactions can also involve transition metal complexes as cations, with [Co(NH3)6] 3+/benzene interaction being very strong (-31.4 kcal/mol), while [Zn(H2O)6]2+/benzene interaction somewhat weaker (-14.0 kcal/mol). Anion-π interactions of unsubstituted aromatic rings without heteroatoms are possible if they are ligands in organometallic half-sandwich complexes with electron-withdrawing ligands. The anion-π interactions of such transition metal complexes with halides can reach the energy of -25.0 kcal/mol, and they are stronger than anion-π interactions of organic aromatic molecules.