The discovery of new dioxygen binding and activation modes is of paramount importance in biological and synthetic systems. Herein, we describe two rare earth-alkali metal clusters displaying unusual reactivity with dioxygen. We isolate a trans-end-on peroxo dineodymium tetrapotassium species, (LH4Nd)2(trans-μ-η1:η1-O2)K4(thf)4 (5), from reduction reactions of LH5Nd (1) and KLH4Nd (2) employing KC8 in dry O2. Cluster 5 contains the first end-on peroxo coordination to an f-block metal. Surprisingly, when the weaker reductant sodium naphthalenide (NaC10H8) is used, we isolate the cluster (LH4Nd)2(μ6-O)Na4(thf)4 (6), indicating dioxygen's O-O bond has been cleaved. The typically weak π-backbonding interaction of 4f-block elements to stabilize the end-on binding mode of O2 is realized in 5 through a Lewis acid-assisted support of the peroxo species. Cleaving of the O-O bond in 6 is attributed to an increased Lewis acid effect rather than a larger chemical potential driving force since |Ered(KC8)| > |Ered (C10H8-|. Lanthanide oxos are highly reactive; however, the oxo reactivity in 6 is tamed by dimerization and protection with four equatorial closely associated Na ions. This work demonstrates a synergistic effect between the rare earth and alkali metals in the binding and activation of dioxygen and provides a novel route to examine lanthanide peroxo/oxo chemistry.
Xu et al. (Fri,) studied this question.