NDLI: Highly Reactive Porphyrin-Iron-Oxo Derivatives Produced by Photolyses of Metastable Porphyrin-Iron(IV) Diperchlorates

Content Provider	PubMed Central
Author	Pan, Zhengzheng Wang, Qin Sheng, Xin Horner, John H. Newcomb, Martin
Abstract	Photolyses of metastable porphyrin-iron(IV) diperchlorates in laser flash photolysis reactions gave highly reactive transients. The systems studied were 5,10,15,20-tetraphenylporphyrin (TPP), 5,10,15,20-tetramesitylporphyrin (TMP), and 2,3,7,8,12,13,17,18-octaethylporphyrin (OEP). The new species, which decayed within milliseconds in acetonitrile solutions, were shown to react with organic substrates by oxo-transfer reactions involving insertions into carbon-carbon double bonds of alkenes and styrenes or benzylic carbon-hydrogen bonds of arenes. The order of reactivity was OEP > TPP > TMP. Second-order rate constants for reactions with several substrates at 22°C were determined; representative values of rate constants for the TPP derivative were k = 8.6 × 105 M−1 s−1 for styrene, k = 2.5 × 106 M−1 s−1 for cyclohexene, and k = 7.7 × 104 M−1 s−1 for ethylbenzene. These porphyrin-iron-oxo transients reacted 4 to 5 orders of magnitude faster than the corresponding iron(IV)-oxo porphyrin radical cations with rate constants similar to those of porphyrin-manganese(V)-oxo derivatives. Rate constants for oxidations of benzylic C-H positions of arenes correlated with the C-H bond dissociation energies, and Hammett correlations for reactions with substituted styrenes had ρ+ values ranging from −0.5 to −0.7 reflecting electrophilic character of the oxidants and their high reactivity. On the basis of their unique UV-visible spectra, high reactivities, and oxo-transfer properties, the new transients are tentatively identified as porphyrin-iron(V)-oxo perchlorates, electronic isomers (or valence tautomers) of well known iron(IV)-oxo porphyrin radical cations.
Related Links	http://dx.doi.org/10.1021/ja807847q
Ending Page	2628
Page Count	8
Starting Page	2621
File Format	PDF
ISSN	00027863
e-ISSN	15205126
Journal	Journal of the American Chemical Society
Issue Number	7
Volume Number	131
Language	English
Publisher Date	2009-02-25
Access Restriction	Open
Subject Keyword	Colloid and Surface Chemistry Biochemistry Chemistry(all) Catalysis Research in Higher Education
Content Type	Text
Resource Type	Article
Subject	Chemistry Colloid and Surface Chemistry Biochemistry Catalysis

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