Analytical Chemistry and Spectroscopy
Wiley InterScience Backfile Collection 1832-2000
Chemistry and Pharmacology
The relative abilities of weak Lewis bases to complex binuclear lanthanide(III) - silver(I) reagents were checked by inter- or intra- molecular competitions. Preferential complexation at one particular site was shown to be determined mainly by the occurrence of well localized π electrons, by the relief of strain effects or by the lack of steric hindrance. In benzofuran and methoxybenzene derivatives oxygen never interacts directly with the silver reagent and plays a role mainly through electronic effects. Unlike oxygen, sulphur in benzo[b]thiophene is the preferred site of complexation with the silver reagent. On complexation with binuclear shift reagents (lanthanide = Eu, Pr, Yb) the 1H NMR shifts were shown to result from several mechanisms. Better insight into the precise location of the reagent is obtained in 13C NMR by the use of the binuclear relaxation reagent Ag(tfa)-Gd(fod)3.
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