Insight into the Ligand-to-Ligand Charge-Transfer Process in Rare-Earth-Metal Diradical Complexes

Abstract

While a ligand-to-ligand charge-transfer (LLCT) process is an important way to understand the interactions between metal-bridged radicals for late-transition-metal complexes, there is little clear and evident observation of the LLCT process for rareearth-metal complexes. In this work, rare-earth-metal diradical complexes supported by diazabutadiene (DAD) ligands [(DAD) 2 RE(BH 4 )] [RE = Yb (1), Sm (2)] were synthesized and studied. The coordination geometries of 1 and 2 are different due to the different ionic radii. Reduction of 1 or 2 generated monoradical complexes, with one of their DAD radical anions being reduced. In all of the complexes, Sm and Yb remain at the 3+ valence state. In their UV−vis spectra, the LLCT transition of 1 could be clearly observed, but complex 2 did not show the same transition. These results could be related to the geometric structures of the complexes as well as exchange coupling between diradicals, thus clearly expanding the model for late-transition-metal-bridged diradicals to rare-earth systems experimentally.

Bi-Catalyzed Trifluoromethylation of C(sp2)–H Bonds under Light

“…On the other hand, the LUMO and LUMO+1 can be described as π* orbitals delocalized throughout the N,C,N -pincer ligand. Therefore, the absorptions in the operating blue light regime are associated with LLCT processes that ultimately reduce the electron density of the hypervalent bonding orbitals and induce Bi–O bond homolysis …”