Labile ligands on some Lewis super acids: a computational study.

Lewis super-acids, like Sn(OTf)(4) or In(OTf)(3), OTf = CF(3)SO(3)(-), are efficient catalysts for cycloisomerization reactions. We report here a study on the coordination of ligands (or of solvent molecules) around such catalysts at density functional theory level. Using the Sn-based compound as an example, we consider the interaction with several molecules, usually nearby in reaction conditions. These include nitromethane, esters and diesters, dimethylsulfoxide, and so on. We establish a ladder of interaction strengths and show that dimethylsulfoxyde molecules can displace triflate ligands from the metallic center. This leads to the main conclusions that solvent molecules directly coordinate Sn centers and that non-coordinating triflates are potentially free in solution despite their anionic characteristic.