Divalent Tetra- and Penta-phenylcyclopentadienyl Europium and Samarium Sandwich and Half-Sandwich Complexes: Synthesis, Characterization, and Remarkable Luminescence Properties
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posted on 2015-12-14, 00:00 authored by Rory P. Kelly, Toby D.
M. Bell, Rosalind P. Cox, Daisy P. Daniels, Glen B. Deacon, Florian Jaroschik, Peter C. Junk, Xavier F. Le Goff, Gilles Lemercier, Agathe Martinez, Jun Wang, Daniel WernerThe 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 redox-transmetalation/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 variable-temperature 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.
