54453-30-4Relevant academic research and scientific papers
Kinetic study of the reaction of ferric porphyrin fluorides and imidazole
Jones,Tondreau,Edwards,Sweigart
, p. 296 - 300 (2008/10/08)
A kinetic study is reported for the reaction of Fe(porphyrin)F (porphyrin = dianion of tetraphenylporphyrin (TPP) and protoporphyrin IX dimethyl ester (PPIXDME)) with imidazole (HIm) in acetone at 25°C to give Fe(porphyrin)(HIm)2+F-. The reaction rate shows a complex dependence on the HIm concentration, being second order in HIm at low concentrations and progressing to zero order at high concentrations of HIm. With Fe(TPP)F, optical spectra at 25 and -78°C show the existence of two reaction intermediates. The first intermediate to form is the six-coordinate high-spin Fe(TPP)(HIm)F and the second is Fe(TPP)(HIm)F?HIm, in which an external imidazole is hydrogen bonded to the fluoride. Thus, hydrogen bonding is shown to play a major role in assisting ionization of the fluoride. A comparison to analogous Fe(porphyrin)Cl complexes shows that hydrogen bonding is much more important with the fluoride, as expected for the stronger Br?nsted base (F- compared to Cl-). A complete analysis of the data is provided that yields rate constants as well as equilibrium constants for the formation of both intermediates. The relevance of these reactions to hydrogen bonding to superoxide in oxymetalloporphyrins is noted.
