MIXED-LIGAND LANTHANIDE COMPLEXES .8. PARAMAGNETIC SHIFT INDUCED BY PR(FOD)3PZ AND PR(FOD)3PYZ IN THE NMR-SPECTRUM OF DI-N-BUTYL ETHER

Two adducts of Pr(fod)(3), Pr(fod)(3)pz and Pr(fod)(3)pyz, where pz st ands for pyrazole and pyz for pyrazine, have been scanned as potential NMR shift reagents using di-n-butyl ether. Although di-n-butyl is a v ery weak donor, complexes associate with the base and induce large hyp erfine isotropic shifts in the resonance frequencies of the magnetic s ubstrate nuclei. The t-butyl resonances of the complexes are strongly shifted upfield in the presence of the substrate. This observation, to gether with the fact that the spectrum of the substrate is unaffected by the addition of any amount of the complexes, are taken as evidence that the specific coordination of the complexes to the substrate occur s through the agency of the oxygen lone-pair electrons.