Guanidinate Yttrium Complexes Containing Bipyridyl and Bis(benzimidazolyl) Radicals.

Ancillary ligand scaffolds that sufficiently stabilize a metal ion to allow its coordination to an open-shell ligand are scarce, yet their development is essential for next-generation spin-based materials with topical applications in quantum information science. To this end, a synthetic challenge must be met: devising molecules that enable the binding of a redox-active ligand through facile displacement and clean removal of a weakly coordinating anion. Here, we probe the accessibility of unprecedented radical-containing rare-earth guanidinate complexes by combining our recently discovered yttrium tetraphenylborate complex [{(MeSi)NC(NPr)}Y][(μ-η-Ph)(BPh)] with the redox-active ligands 2,2'-bipyridine (bpy) and 2,2'-bis(benzimidazole) (Bbim), respectively, under reductive conditions. Our endeavor resulted in the first evidence of guanidinate complexes that contain radicals, namely, a mononuclear bipyridyl radical complex, {(MeSi)NC(NPr)}Y(bpy) (), and a dinuclear bis(benzimidazolyl) radical-bridged complex, [K(crypt-222)][{(MeSi)NC(NPr)}Y](μ-Bbim) (). The latter was achieved by an in situ reduction of [{(MeSi)NC(NPr)}Y](μ-Bbim) (), which was isolated from a salt metathesis reaction. and were characterized by X-ray crystallography and IR and UV-vis spectroscopy. Variable-temperature electron paramagnetic resonance spectroscopy was applied to gain insight into the distribution of unpaired spin density on and . Density functional theory calculations were conducted on and to elucidate further their electronic structures. The redox activity of and was also probed by electrochemical methods.