Solution versus Solid-State Structure of Ytterbium Heterobimetallic Catalysts

• Published in: Journal of the American Chemical Society 2003-05, Vol.125 (18), p.5549-5558
• Main Authors: Di Bari, Lorenzo, Lelli, Moreno, Pintacuda, Guido, Pescitelli, Gennaro, Marchetti, Fabio, Salvadori, Piero
• Format: Article
• Language: English
• Subjects: Condensed matter: structure, mechanical and thermal properties; Exact sciences and technology; Inorganic compounds; Metal complexes; Physics; Structure of liquids; Structure of simple liquids; Structure of solids and liquids; crystallography; Structure of specific crystalline solids
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/ja0297640

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 C 3 symmetry into the solution D 3 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.