Investigation of the [Sm{N(SiMe3)2}2] reducing system in THF.: Rate and mechanistic studies

The reductant [Sm{N(SiMe3)(2)}(2)] was examined by cyclic voltammetry and UV-vis spectroscopy. Rate constants and activation parameters for the reduction of 1-iodobutane, 2-butanone, and methylacetoacetate by [Sm{N(SiMe3)(2)}(2)] were measured in THF by stopped-flow absorption decay experiments. Comparison with Sml(2) and Sml(2)-HMPA shows that the redox potential of [Sm{N(SiMe3)(2)}(2)] is intermediate between the Sml(2)-based reductants, yet it reduces alkyl iodides and ketones at a faster rate than the powerful combination of Sml(2) and HMPA. The activation data for reduction of alkyl iodides and ketones by [Sm{N(SiMe3)(2)}(2)] are consistent with highly ordered transition states having low activation barriers. All of these results taken together suggest that the mechanism of reduction of alkyl iodides and ketones by [Sm{N(SiMe3)(2)}2] has more inner-sphere character than reduction by Sml(2) or Sm-(HMPA) complexes. The change in the ET mechanism is attributed to the unique structure of the [Sm{N(SiMe3)(2)}(2)] complex.