Solution versus Solid-State Structure of Ytterbium Heterobimetallic Catalysts

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.