Multielectron Redox Chemistry of Ytterbium Complexes Reaching the +1 and Zero Formal Oxidation States

Lanthanide redox reactivity remains limited to one-electron transfer reactions due to their inability to access a broad range of oxidation states. Here, we show that multielectron reductive chemistry is achieved for ytterbium by using the tripodal tris(siloxide)arene redox-active ligand, which can store two electrons in the arene anchor. Reduction of the Yb(III) complex of the tris(siloxide)arene tripodal ligand affords the Yb(II) analogue by metal-centered reduction. Two subsequent reduction events occur mainly at the ligand with retention of the ligand framework and formation of analogous complexes of Yb in the formal +1 and zero oxidation states. Four complexes of Yb in four different oxidation states were isolated, crystallographically and spectroscopically characterized, and their electronic structure was confirmed by DFT studies. Reactivity studies show that the "Yb(I)" complex can transfer two electrons to organic azides, with retention of its molecular structure, to form highly reactive imido intermediates, providing a rare example of a two-electron transfer at a single lanthanide center that does not involve accessing the +4 oxidation state.