Evaluating Electron Transfer Reactivity of Rare-Earth Metal(II) Complexes Using EPR Spectroscopy

摘要

To evaluate the relative reducing capacities of rare-earth metal complexes of Sc(II), Y(II), and complexes of the lanthanide metals in their +2 oxidation state, a series of reactions of trivalent Ln(III)A(3) compounds with divalent [Ln'(III)A(3)'](1-) complexes has been examined, where Ln = Sc, Y, or a lanthanide and A is C5H4SiMe3 (Cp'), C5H3(SiMe3)(2) (Cp ''), C5Me4H (Cp-tet), N(SiMe3)(2) (NR2), 2,6-Bu-2-C6H3O (OAr), or 2,6-Bu-t(2)-4-MeC6H2O (OAr'). The specific combinations were chosen to allow evaluation by EPR spectroscopy of the Ln(II) complex. The [Ln(II )Cp(3)'](1- )complexes of Y(II), La(II), and Lu(II) have similar reducing abilities in that they all reduce Ln(III)Cp(3)' complexes of the other metals in this group. However, these Y(II), La(II), and Lu(II) complexes all are stronger reductants than [(GdCp3)-Cp-II'](1-), which cannot reduce Ln(III)Cp(3)' complexes of Y, La, and Lu. These results do not apply to all ligand sets, since [Gd-II(NR2)(3)](1-) can reduce Y-III(NR2) 3 to [Y-II(NR2)(3)](1-). The amide and aryloxide complexes of Y and Sc are similar in that [Y-II(NR2)(3)](1-) reduces Sc-III(NR2)(3) and [Y-II(NR2)(3)](1-) reduces Sc-III(OAr')(3). Both [Y-II(NR2)(3)](1-) and [Y-II(OAr')(3)](1-) reduce (YCp3)-Cp-III'. [(LaCp3tet)-Cp-II](1- )has reductive capacity similar to that of [(LaCp)-Cp-II'(3)](1-), and both are stronger reductants than [(LaCp)-Cp-III ''(3)](1-). None of the Ln(III)I(2) complexes of Sm, Tm, Dy, and Nd can reduce Ln(III)A(3 )complexes of Y and La to [Ln(II)A(3)](1-). In the "same-metal-differentligands" reactions, multiple EPR signals are found, suggesting that ligand exchange occurs alongside the electron transfer reactivity.