Kinetics of binding of O2 and CO to 'double-sided' porphyrinatoiron(II) complexes

Teruyuki Komatsu, Etsuo Hasegawa, Shin Ichi Kumamoto, Hiroyuki Nishide, Eishun Tsuchida

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Abstract

The kinetics of binding of O2 and CO to double-sided porphyrinatoiron(II) complexes having ester pockets on both sides of the porphyrin plane has been studied. The specific environment created by the four ester groups around the central iron(II) ion of 5,10,15,20-tetrakis(2,6-di-tert-butylacetoxyphenyl)porphyrinatoiron(II) 2 results in binding which is not affected by solvation. The lower binding affinity for CO of 5,10,15,20-tetrakis(2,6-dipivaloyloxyphenyl)porphyrinatoiron(II) 1 compared to that of 5,10,15,20-tetra (o-pivalamidophenyl)porphyrinatoiron(II) is attributed to the unfavourable steric repulsions between the axial imidazole ligand and the pivaloyloxy groups, and is reflected in decreased association and increased dissociation rates. On the other hand, axial base ligation to 2 is not inhibited by the tert-butylacetoxy groups. Therefore, the lower binding affinity for O2 exhibited by 2 compared to that of an amide fenced porphyrin complex is ascribed to the loss of local polarity in the cavity. The less-polar ester groups of the double-sided porphyrinatoiron complex result in an increased rate of dissociation of O2. The activation energy for gaseous ligand association to complex 2 was determined.

Original languageEnglish
Pages (from-to)3281-3284
Number of pages4
JournalJournal of the Chemical Society, Dalton Transactions
Issue number12
DOIs
Publication statusPublished - 1991

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Carbon Monoxide
Esters
Kinetics
Porphyrins
Association reactions
Ligands
Solvation
Amides
Iron
Activation energy
Ions
porphyrinatoiron(II)

ASJC Scopus subject areas

  • Chemistry(all)

Cite this

Kinetics of binding of O2 and CO to 'double-sided' porphyrinatoiron(II) complexes. / Komatsu, Teruyuki; Hasegawa, Etsuo; Kumamoto, Shin Ichi; Nishide, Hiroyuki; Tsuchida, Eishun.

In: Journal of the Chemical Society, Dalton Transactions, No. 12, 1991, p. 3281-3284.

Research output: Contribution to journalArticle

Komatsu, Teruyuki ; Hasegawa, Etsuo ; Kumamoto, Shin Ichi ; Nishide, Hiroyuki ; Tsuchida, Eishun. / Kinetics of binding of O2 and CO to 'double-sided' porphyrinatoiron(II) complexes. In: Journal of the Chemical Society, Dalton Transactions. 1991 ; No. 12. pp. 3281-3284.
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AB - The kinetics of binding of O2 and CO to double-sided porphyrinatoiron(II) complexes having ester pockets on both sides of the porphyrin plane has been studied. The specific environment created by the four ester groups around the central iron(II) ion of 5,10,15,20-tetrakis(2,6-di-tert-butylacetoxyphenyl)porphyrinatoiron(II) 2 results in binding which is not affected by solvation. The lower binding affinity for CO of 5,10,15,20-tetrakis(2,6-dipivaloyloxyphenyl)porphyrinatoiron(II) 1 compared to that of 5,10,15,20-tetra (o-pivalamidophenyl)porphyrinatoiron(II) is attributed to the unfavourable steric repulsions between the axial imidazole ligand and the pivaloyloxy groups, and is reflected in decreased association and increased dissociation rates. On the other hand, axial base ligation to 2 is not inhibited by the tert-butylacetoxy groups. Therefore, the lower binding affinity for O2 exhibited by 2 compared to that of an amide fenced porphyrin complex is ascribed to the loss of local polarity in the cavity. The less-polar ester groups of the double-sided porphyrinatoiron complex result in an increased rate of dissociation of O2. The activation energy for gaseous ligand association to complex 2 was determined.

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