New Dinuclear 5-<i>a</i><i>nsa</i>-Lanthanocene Derivatives. Crystal Structures of [Ln{2,6-(CH<sub>2</sub>C<sub>5</sub>H<sub>4</sub>)<sub>2</sub>C<sub>5</sub>H<sub>3</sub>N}μ-O<sub>2</sub>SOCF<sub>3</sub>]<sub>2</sub> (Ln = Nd, Y, Yb) and a VT Solution NMR (<sup>1</sup>H, <sup>19</sup>F) Study of the Fluxional Yttrium Homologue
作者:Gino Paolucci、Jacopo Zanon、Vittorio Lucchini、Wulf-Erich Damrau、Eric Siebel、R. Dieter Fischer
DOI:10.1021/om0104868
日期:2002.3.1
Five homologues of the new complex series [LnL(mu-OTf)](2) with Ln = Pr (1), Nd (2), Sm (3), Y (4), Yb (5) have been prepared from [Ln(OTf)(3)] and Na2L, where L designates two cyclopentadienyl rings tethered by a 2,6-bis(methylene)pyridyl unit and -OTf the triflate (trifluoromethanesulfonate) anion. According to crystal structure analyses of 2, 4, and 5, each triflate ligand bridges two Ln ions (Ln-O-S(O)-O'-Ln'), while, owing to substantial Ln-N(pyridyl) bonding, the LnL fragments turn out to be notably rigid entities. Nevertheless, the variable-temperature (VT) H-1 NMR spectra of all complexes reveal notable fluxionality. According to a detailed VT F-19 NMR study of 4, two dinuclear isomers, differing in the trans and cis orientations, respectively, of their two L fragments, interconvert with a negligibly small entropy of activation DeltaS(double dagger). A motion reminiscent of the Berry turnstile would most plausibly explain the experimental findings.