Addition of HMPA to [Sm{N(SiMe3)2}2] produces a less reactive reductant in contrast to additionof HMPA to SmI2. While the [Sm{N(SiMe3)2}2]-HMPA combination results in a more powerful reductantbased on the redox potential, the observed decrease in reactivity is attributed to steric hindrance causedby the nonlabile ligand -N(SiMe3)2 and HMPA around the Sm metal. The importance of ligand displacement(exchange) in Sm(II)-HMPA-based reactions and insight into the mechanism of [Sm{N(SiMe3)2}2]-HMPAand SmI2-HMPA reductions are presented.