Binuclear lanthanide(III)–silver(I) NMR shift reagents: Investigations of new achiral and chiral analogs

A series of new achiral binuclear complexes formed from a ytterbium(III) tris‐beta‐diketonate and silver(I) beta‐diketonate have been evaluated as NMR shift reagents for olefins. The effectiveness of the new reagents was compared with that of similar binuclear reagents that have already been reported. Some unexpected behavior in the form of ‘wrong way’ shifts was observed in the NMR spectrum of substrates in the presence of certain binuclear reagents. Possible explanations for this observation are discussed. A series of new chiral binuclear reagents were evaluated; certain of the complexes with praseodymium(III) resulted in enhanced enantiomeric resolution when compared with previously reported examples. Binuclear complexes formed from Pr(III) tris chelates with the ligands d,d‐dicampholylmethane and 1,1‐difencholylmethane do not appear to be suitable for chiral binuclear shift reagent applications.

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