Structure and Energetics of the Samarium Diiodide−HMPA Complex in Tetrahydrofuran

Abstract

The role of HMPA as a ligand for SmI₂ and the stoichiometry and energetics of formation for the SmI₂-HMPA complex in THF were investigated employing UV-vis spectroscopy, isothermal titration calorimetry (ITC), and vapor pressure osmometry (VPO). The aggregation number for SmI₂ in THF was found to be 0.98 ± 0.09 over the entire concentration range studied (6.71-84.0 mM), indicating that SmI₂ is monomeric. The UV-vis data suggest that four HMPA ligands coordinate to SmI₂, and this was supported by ITC experiments. The combined results are consistent with [SmI₂(HMPA)₄] being the reductant responsible for the unique reactivity exhibited by SmI₂-HMPA cosolvent combinations.