NUCLEAR MAGNETIC RESONANCE STUDIES OF N-H PROTON DISSOCIATION AND INVERSION OF PLATINUM(II) COMPLEXES OF SUBSTITUTED ETHYLENEDIAMINES

The effects of high KOH concentrations on nmr chemical shifts of ligand protons have been used to determine the fractional extent of titration and pKa's of weakly acidic N-H protons of several Pt(II) complexes. For five methyl-substituted bipyridyl-ethylenediamine complexes, pKa's range from 0.07Kw to 0.20Kw at μ = 1.3. For Pt(NH3)2(N,N′-dmen)2+ and Pt(NH3)2(EDDA), pKa ≅ 0.01Kw. For asymmetric complexes, rate constants for OH−-catalyzed inversion (Kin') have also been determined by analysis of nmr line shapes as a function of pH. Coupled with the pKa determinations, these data permit calculation of k3 (= 105-106 sec−1 at 30° for four complexes), the rate constant for inversion of deprotonated complex. More limited temperature-dependence data suggest that ΔH°N-H; for the ionization of N-H for three complexes ≅ ΔH°H, which requires that ΔHin*, the activation energy derived from the temperature dependence of kin', ≅ ΔH3*, the activation energy for inversion of deprotonated complex. © 1969, American Chemical Society. All rights reserved.