Divalent Tetra- and Penta-phenylcyclopentadienyl Europium and Samarium Sandwich and Half-Sandwich Complexes: Synthesis, Characterization, and Remarkable Luminescence Properties

The synthesis of the bulky divalent (polyphenylcyclopentadienyl)­lanthanoid sandwich complexes [Ln­(C<sub>5</sub>Ph<sub>5</sub>)<sub>2</sub>] (Ln = Sm, Eu) and [Ln­(C<sub>5</sub>Ph<sub>4</sub>H)<sub>2</sub>(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)<sub>4</sub>]­[C<sub>5</sub>Ph<sub>4</sub>H]<sub>2</sub>. In addition, rare divalent samarium halide complexes [Sm­(C<sub>5</sub>Ph<sub>5</sub>)­(μ-Br)­(thf)<sub>2</sub>]<sub>2</sub> and [Sm­(C<sub>5</sub>Ph<sub>4</sub>H)­I­(thf)<sub>3</sub>], were also prepared, either by RTP or ligand rearrangement. X-ray studies showed that the [Ln­(C<sub>5</sub>Ph<sub>5</sub>)<sub>2</sub>] complexes adopt highly symmetrical sandwich structures, whereas the [Ln­(C<sub>5</sub>Ph<sub>4</sub>H)<sub>2</sub>(solv)] complexes have open sandwich structures. The unexpected, but limited, solubility of the [Ln­(C<sub>5</sub>Ph<sub>5</sub>)<sub>2</sub>] complexes allowed for variable-temperature NMR spectra of [Sm­(C<sub>5</sub>Ph<sub>5</sub>)<sub>2</sub>] to be obtained. Detailed 1D and 2D NMR studies were conducted on [Sm­(C<sub>5</sub>Ph<sub>4</sub>H)<sub>2</sub>(thf)] to ascertain its structure in donor and nondonor solvents. During the course of these studies, the mixed tetraarylcyclopentadienyl sandwich complex [Sm­{C<sub>5</sub>(2,5-Ph)<sub>2</sub>­(3,4-<i>p</i>-tol<sub>2</sub>)­H}<sub>2</sub>(thf)] was also prepared in order to fully assign the spectrum of [Sm­(C<sub>5</sub>Ph<sub>4</sub>H)<sub>2</sub>(thf)]. The europium sandwich complexes [Eu­(C<sub>5</sub>Ph<sub>5</sub>)<sub>2</sub>] and [Eu­(C<sub>5</sub>Ph<sub>4</sub>H)<sub>2</sub>(dme)] exhibit remarkable luminescence properties with high quantum yields (45% and 41%, respectively) coupled w<sub>i</sub>th long emission lifetimes (approximately 800 and 1300 ns, respectively) in toluene.