Kinetic H/D/T isotope and solid state effects on the tautomerism of the conjugate porphyrin monoanion
- Freien Universitaet, Berlin (Germany)
- Universitaet Freiburg (Germany)
- Lawrence Berkeley National Lab., CA (United States)
Using dynamic NMR spectroscopy, the kinetic isotope effects of the degenerate single hydron transfer in the conjugate {sup 15}N-labeled porphyrin anion Por-H{sup -} dissolved in organic solvents have been measured as a function of temperature. Por-H{sup -} was generated by dissolving the labeled parent compound porphyrin together with the phosphazene base 1,1,1,5,5, 5-hexakis(dimethylamino)-3-[1,1,2, 2-tetramethylpropylimino]-3-[[tris(dimethylamino)- phosphoran yliden]amino]-1{lambda}{sup 5},3{lambda}{sup 5},5{lambda}{sup 5} 1,1,4-triphosphazadiene (tHept-P{sup 4}) in organic solvents. In addition, by reaction of porphyrin with the base 1,1,1,5,5, 5-tetrakis[tris(dimethylamino)phosphoranylidene]amino phosphonium fluoride(P{sup 5}{sup +}F{sup -}) Por-H{sup -} could be embedded into the solid state and its tautomerism followed by {sup 15}N CPMAS NMR. Surprisingly, within the margin of error, the generacy of the tautomerism was not lifted in the solid state and the rate constants of the proton transfer were identical in the liquid and the solid. The kinetic isotope effects at 240 K (extrapolated) are given by k{sup H}/k{sup D} = 34 and k{sup H}/k{sup T} = 152. The size and the temperature dependence of the isotope effects indicates a proton tunneling mechanism as in the parent porphyrin where this process is nondegenerate. 29 refs., 9 figs., 3 tabs.
- OSTI ID:
- 427056
- Journal Information:
- Journal of the American Chemical Society, Vol. 118, Issue 45; Other Information: PBD: 13 Nov 1996
- Country of Publication:
- United States
- Language:
- English
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