80975-58-2Relevant academic research and scientific papers
Heme carbonyls: Environmental effects on vc-o and Fe-C/C-O bond length correlations
Silvernail, Nathan J.,Roth, Arne,Schulz, Charles E.,Noll, Bruce C.,Scheldt, W. Robert
, p. 14422 - 14433 (2007/10/03)
The synthesis and characterization of four low-spin (carbonyl)iron(11) tetraphenylporphyrinates, [Fe(TPP)(CO)(L)], where L = 1-methylimidazole, 2-methylimidazole, 1,2-dimethylimidazole (unsolvated), and 1,2-dimethylimidazole (toluene solvate) are reported. The complexes show nearly the same value of vc-o in toluene solution (1969-72 cm-1) but a large range of CO stretching frequencies in the solid-state (1926-1968 cm-1). The large solid-state variation results from CO interactions in the solid state, as shown by an examination of the crystal structures of the four complexes. The high precision of the four structures obtained allows us to make a number of structural and spectroscopic correlations that describe the Fe-C-O and N lm-Fe-CO units. The values of vc-o and the Fe-C and C-O bond distances are strongly correlated and provide a structural, as well as a spectroscopic, correlation of the π back-bonding model. The interactions of CO described are closely related to the large range of CO stretching frequencies observed in heme proteins and specific interactions observed in carbonylmyoglobin (MbCO).
O2 and CO Binding to Iron(II) Porphyrins: A Comparison of the Picket Fence and Pocket Porphyrins
Collman, James P.,Brauman, John I.,Iverson, Brent L.,Sessler, Jonathan L.,Morris, Roger M.,Gibson, Quentin H.
, p. 3052 - 3064 (2007/10/02)
Kinetic and equilibrium O2 and CO binding behavior for various iron(II) porphyrin systems are reported.Compared to the picket fence complexes, unprotected iron(II) porphyrins have both lowered affinities and lowered ligand association rates.This is explained in terms of a solvation effect which stabilizes the five-coordinate form in the unprotected iron(II) porphyrins.Five-coordinate iron(II) complexes of the sterically encumbered medium and small pocket porphyrins show substantially reduced CO affinities as compared to the analogous open-cavity picket fence complexes.Kinetic data indicate that the lowered CO affinities in the pocket complexes are primarily reflected in decreased assosiation rates.By contrast, the pocket models show both decrease O2 dissociation and association rates as compared to the picket fence analogues.As such, the O2 affinities are virtually identical throughout the series of picket and picket fence complexes.These results are discussed in terms of distal-side steric interactions.
Ligand, Oxygen, and Carbon Monoxide Affinities of Iron(II) Modified Capped Porphyrins
Hashimoto, Toshiaki,Dyer, Robert L.,Crossley, Maxwell J.,Baldwin, Jack E.,Basolo, Fred
, p. 2101 - 2109 (2007/10/02)
Ligand, O2, and CO binding constants are presented for iron(II) modified capped porphyrins.Steric effects at the axial position outside the cap were altered by changing a tetraphenyl-type cap to a corresponding tetranaphthalene-type cap.The steric hindrance caused by the peri hydrogens of the naphthalene groups is believed to be responsible for the decrease in ligation in the order n-propylamine > isobutylamine > sec-butylamine > tert-butylamine.Inductive effects in the porphyrin plane were altered by introducing a nitro group.Such an electron-withdrawing group enhances ligation but retards oxygenation.The solvent effect on O2 binding by capped complexes is small, presumably because the environment of the O2 bound inside the cap is not greatly changed by changes in solvent.The CO affinities of iron(II) capped porphyrins and of corresponding iron(II) flat-open porphyrins are similar.In contrast, the O2 affinities of the capped systems are lower than their flat-open counterparts, which means the iron(II) capped porphyrin complexes discriminate against O2 but not CO.This is discussed in terms of distal steric effects on the stable structures of Fe-O-O (bent) and Fe-C-O (linear).
