Structure and energetics of the samarium diiodide-HMPA complex in tetrahydrofuran

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 W -vis spectroscopy, isothermal titration calorimetry (ITC), and vapor pressu re 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), i ndicating that SmI2 is monomeric. The UV-vis data suggest that four HMPA li gands coordinate to SmI2, and this was supported by ITC experiments. The co mbined results are consistent with [SmI2(HMPA)(4)] being the reductant resp onsible for the unique reactivity exhibited by SmI2-HMPA cosolvent combinat ions.