Molecular Structures of HMPA-Coordinated Samarium(II) and Ytterbium(II) Iodide Complexes. A Structural Basis for the HMPA Effects in SmI2-Promoted Reactions

The reaction of ytterbium(II) iodide (YbI2) with 4.5 equiv of hexamethylphosphoric triamide (hmpa) in tetrahydrofuran (thf) gave [Yb(hmpa)4(thf)2]I2 (1) as yellow crystals. A similar reaction of SmI2 with hmpa afforded black-purple [SmI2(hmpa)4] (2) after recrystallization from toluene. When 10 equiv of hmpa were used in the reaction with SmI2, [Sm(hmpa)6]I2 (3) was obtained as purple blocks. Complexes 1—3 have been structurally characterized by crystallographic studies. The structural data of these complexes satisfactorily explain the hmpa effects observed in SmI2-promoted reactions, and also provide a guideline for the use of HMPA in these reactions.