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Solution versus Solid-State Structure of Ytterbium Heterobimetallic Catalysts

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posted on 15.04.2003 by Lorenzo Di Bari, Moreno Lelli, Guido Pintacuda, Gennaro Pescitelli, Fabio Marchetti, Piero Salvadori
The solution structures of the ytterbium heterobimetallic complexes Na3[Yb((S)-BINOL)3] (1), K3[Yb((S)-BINOL)3] (2), and Li3[Yb((S)-BINOL)3] (3), belonging to a family of well-known enantioselective catalysts, are studied by means of NMR and circular dichroism (CD) in the UV and near-IR regions. The experimental NMR paramagnetic shifts were employed to obtain a refined solution structure of 1. NMR analysis demonstrated that 1, 2, and 3 have the same solution geometry but different magnetic susceptibility anisotropy 𝒟 factors. By comparing XRD and NMR structures of 1, we demonstrate that, upon dissolution, this complex experiences a rearrangement from the crystalline C3 symmetry into the solution D3 symmetry. Remarkably, Yb is not bound to water in solution, and Ln−BINOL bonds are labile as demonstrated through EXSY. NIR−CD is confirmed especially sensitive to changes in the ytterbium coordination sphere.