Solution structure and structural rearrangement in chiral dimeric ytterbium(iii) complexes determined by paramagnetic NMR and NIR-CD

Abstract

Chiral lanthanide complexes are attracting interest in enantioselective catalysis and due to their unique optical and magnetic properties. Here, we investigate the chiral ytterbium complex [Yb((S)-THP)] ((S)-THP = ((1S,4S,7S,10S)-1,4,7,10-tetrakis(2-hydroxypropyl)-1,4,7,10-tetraazacyclododecane), which has found applications in catalysis and as a CEST agent in MRI, by means of near-IR circular dichroism (NIR CD), NMR, and mass spectrometry, in different solvents. The NMR analysis revealed that this complex, different from the analogues including early lanthanides, is not axially coordinated by the solvent. In non-protic solvents, and in the presence of bases, [Yb((S)-THP)]³⁺ dimerizes to [Yb((S)-H₂THP)]₂²⁺. The careful analysis of the paramagnetic contributions in the NMR spectra allowed us to determine the structure of the dimeric species in solution, revealing a structural rearrangement of the coordination cage following the dimerization process.