NMR study of lanthanide shift reagents.

The work in this thesis describes a detailed study of the nature of the interactions occurring in solution between lanthanide shift reagents and organic substrates. The determination of intrinsic parameters, such as equilibrium binding constants and limiting incremental shift values feature prominently in this work. Chapter I gives a brief outline of the historical background and the chemistry of lanthanide shift reagents, namely, chelates of rare-earth ions and selected beta-diketones. In the first part of Chapter II, an account is presented of the experimental conditions that need to be considered for the determination of reliable intrinsic parameters. An account of simple data treatment methods used to determine intrinsic parameters is also presented. The results of these determinations are discussed in terms of assumed 1:1 and 2:1 stoichiometries. The second part of Chapter II describes a rigorous data treatment method for determining intrinsic parameters. A discussion of the results obtained for a series of alcohols, ketones, ethers and nitrogen containing substrates complexed with the shift reagent Eu(fod)[3], is also presented. Selected results of the rigorous data treatment method are then compared with results from simple data treatment methods. Chapter III describes several independent, but simple data treatment methods which may be used as alternatives to the data treatment method presented in Chapter II. These methods employ shift reagent resonance frequencies and also competition experiments involving two competing substrates. In view of the expected complexity of the solution equilibria for a 2:1 stoichiometry, only those systems exhibiting a predominantly 1:1 stoichiometry have been considered. In Chapter IV an account of the contact and pseudocontact lanthanide induced shift mechanisms is presented. Various methods for separating the contact shift contribution from the total paramagnetic induced shift are then described. Contact shifts for several substituted pyridine-Eu(fod)[3] complexes are determined and the results discussed in terms the symmetry of the shift reagent-substrate complex.