Divalent Tetra- and Penta-phenylcyclopentadienyl Europium and Samarium Sandwich and Half-Sandwich Complexes: Synthesis, Characterization, and Remarkable Luminescence Properties
Résumé
The synthesis of the bulky divalent
(polyphenylcyclopentadienyl)lanthanoid sandwich complexes
[Ln(C5Ph5)2] (Ln = Sm, Eu) and [Ln(C5Ph4H)2(solv)] (Ln =
Sm, solv = thf; Ln = Eu, solv = dme)], from redoxtransmetalation/
protolysis (RTP) reactions, has been
achieved. An analogous reaction with Yb afforded the
solvent-separated ion pair [Yb(dme)4][C5Ph4H]2. In addition,
rare divalent samarium halide complexes [Sm(C5Ph5)(μ-
Br)(thf)2]2 and [Sm(C5Ph4H)I(thf)3], were also prepared,
either by RTP or ligand rearrangement. X-ray studies showed
that the [Ln(C5Ph5)2] complexes adopt highly symmetrical sandwich structures, whereas the [Ln(C5Ph4H)2(solv)] complexes
have open sandwich structures. The unexpected, but limited, solubility of the [Ln(C5Ph5)2] complexes allowed for variabletemperature
NMR spectra of [Sm(C5Ph5)2] to be obtained. Detailed 1D and 2D NMR studies were conducted on
[Sm(C5Ph4H)2(thf)] to ascertain its structure in donor and nondonor solvents. During the course of these studies, the mixed
tetraarylcyclopentadienyl sandwich complex [Sm{C5(2,5-Ph)2(3,4-p-tol2)H}2(thf)] was also prepared in order to fully assign the
spectrum of [Sm(C5Ph4H)2(thf)]. The europium sandwich complexes [Eu(C5Ph5)2] and [Eu(C5Ph4H)2(dme)] exhibit
remarkable luminescence properties with high quantum yields (45% and 41%, respectively) coupled with long emission lifetimes
(approximately 800 and 1300 ns, respectively) in toluene.