Tuning Lanthanide Reactivity Towards Small Molecules with Electron‐Rich Siloxide Ligands

Abstract

The synthesis, structure, and reactivity of stable homoleptic heterometallic LnL 4 K 2 complexes of divalent lanthanide ions with electron-rich tris(tert-butoxy)siloxide ligands are reported. The [Ln(OSi(OtBu) 3 ) 4 K 2 ] complexes (Ln = Eu, Yb) are stable at room temperature, but they promote the reduction of azobenzene to yield the KPhNNPh radical anion as well as the reductive cleavage of CS 2 to yield CS 3 2À as the major product. The Eu III complex of the radical anion PhNNPh is structurally characterized. Moreover, [Yb(OSi(OtBu) 3 ) 4 K 2 ] can reduce CO 2 at room temperature. Release of the reduction products in D 2 O shows the quantitative formation of both oxalate and carbonate in a 1:2.2 ratio. The bulky siloxide ligands enforce the labile binding of the reduction products providing the opportunity to establish a closed synthetic cycle for the Yb II -mediated CO 2 reduction. These studies show that the presence of four electron-rich siloxide ligands renders their Eu II and Yb II complexes highly reactive.

Lanthanoid Complexes as Molecular Materials: The Redox Approach

“…Although the existence of Ln II in solid state materials had been known for many years, it has taken much longer for molecular Ln II species to be isolated. The more accessible Ln II ions (Eu, Sm, and Yb) have been reasonably well explored in molecular species, and continue to gain attention for applications such as reduction reagents, catalysts, and for small molecule activation [20a, 52] . Among the first Ln II complexes to be reported were those featuring the bulky cyclopentadienyl (Cp) and cyclooctatetraene (COT) ligands, [53] phosphane, [54] selenolate, [55] and silylamide ligands (Scheme 1).…”