Divalent samarium in new coordination environments: Structure and reactivity

The chemistry of divalent samarium has been studied extensively in recent years. However, only three reagents have been extensively investigated. In organolanthanide laboratories, the pentamethylcyclopentadienide reagents, {dollar}rm{lcub}(Csb5Mesb5)sb2Sm(THF)sb2{rcub}{dollar} and {dollar}rm (Csb5Mesb5)sb2Sm{dollar}, are the most widely studied. In synthetic organic laboratories, the samarium reagent of choice is SmI{dollar}sb2{dollar}(THF){dollar}sb{lcub}rm x{rcub}{dollar}. Although each of these reagents has been shown to effect unique transformations in organic molecules, the pentamethylcyclopentadienide reagents have not been examined for synthetic organic purposes. The goal of this dissertation research was to learn more about the Sm(II) system used in organic synthesis and to develop new Sm(II) reagents for organic synthesis. This was accomplished in two ways. First, since samarium diiodide had not previously been structurally characterized, its structure was determined. The structure was found to be a pentagonal bipyramid in which two iodides occupy the axial positions and five THF molecules occupy the equatorial sites in the molecule, i.e. {dollar}rm{lcub}SmIsb2(THF)sb5{rcub}{dollar}. This coordination geometry was shown to be common for samarium diiodide when in the presence of THF ligands. Secondly, it was of interest to find new ligand sets for samarium(II) that would give reactivity similar to that observed in the pentamethylcyclopentadienide complexes and would be of interest to organic chemists. Two ligands were chosen, indenide and fluorenide, that are structurally similar to pentamethylcyclopentadienide but are less expensive. Two new samarium(II) reagents were made, {dollar}rm {lcub}(CqHsb7)sb2Sm(THF)sb3{rcub}{dollar} and {dollar}rm {lcub}(Csb{lcub}13{rcub}Hsb9)sb2Sm(THF)sb2{rcub}{dollar}, and structurally characterized. These compounds have bent metallocene structures similar to the structures of the pentamethylcyclopentadienide complexes, but differences in the bond angles and coordination number suggested that the reactivity of the new compounds would be different. This was indeed found to be true when the reactivity of the new reagents was probed by examining reactions that were characteristic of the pentamethylcyclopentadienide reagents. It was found that the reductive reactivity of the new reagents was similar to that of the pentamethylcyclopentadienide reagents, but the reaction products were not analogous to the products obtained from the reactions with the pentamethylcyclopentadienide reagents.