PROTON MAGNETIC RESONANCE STUDIES OF AMINO ACID COMPLEXES OF PLATINUM(2) .3. ISOMERISM PROTON EXCHANGE AND INVERSION AT ASYMMETRIC COORDINATED NITROGENS

Rates of N-H proton exchange of 1 and 2 were determined (a) by analysis of line-shape changes of H2O solutions at high pH and (b) by analysis of slow spectral changes of D2O solutions at mid pH. The exchange reactions are OH- catalyzed. However, intramolecular catalysis by acetate fragments is also important in the mid-pH range. Rates of inversion were determined by line-shape analysis of the acetate methylene AB quartet at high pH. Inversion rates were found to be less than N-H proton exchange rates by a factor of 70. The rate of inversion of the deprotonated nitrogen of Pt(NH3)2(EDDA) was determined to be 105-106 sec-1 at 39° on the basis of an nmr-determined N-H acid dissociation constant, Ka ≅ 0.01Kw. Activation energies for inversion of 1 and 2 are 14-16 kcal. Conformational implications of nmr parameters, including JPt-H, are also considered. © 1969, American Chemical Society. All rights reserved.