Nuclear Magnetic Resonance Studies of Terpenes with Chiral and Achiral Lanthanide(III)-Silver(I) Binuclear Shift Reagents

Article abstract of DOI:10.1021/ja00366a003

Certain binuclear metal β-diketonate complexes consisting of a lanthanide(III) tetrakis chelate anion with a silver(I) counterion are effective NMR shift reagents for olefinic and aromatic substrates.The silver in the pair forms a bond with the olephinic or aromatic,and shifts are observed in the NMR spectrum of the substrate because of the proximity of the paramagnetic lanthanide.Significant alterations are produced in the complex NMR spectra of terpenes such as α- and β-pinene, camphene, and Δ-3-carene in the presence of these shift reagents.In contrast with the excellent shifts in the spectra of olefins and aromatic compounds observed with fluorinated β-diketonate complexes of 6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedione or (trifluoroacetyl)-d-camphor, shifts with 2,2,6,6-tetramethyl-3,5-heptanedione chelates are much smaller.In addition, through proper choice of a choral lanthanide chelate and silver β-diketonate, it is possible to distinguish certain dextro and levo resonances of enantiomers.