Cyanide Coordination to Iron(III) Porphyrins and Covalently Linked Diiron(III) Diporphyrins

Wołowiec, Stanisław; Latos‐Grażyński, Lechosław

doi:10.1021/ic00094a022

Cited by 16 publications

(9 citation statements)

References 4 publications

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“…However, compared to related tripodal tetradentate ligands, TMPA is known to favor Cu(II) relative to Cu(I), based on electrochemical redox-potential comparisons. , When [Cu II (TMPA)(CN)]PF 6 ( 2-(PF 6 ) ) is combined in a 2:1 molar ratio with (F 8 -TPP)Fe-PF 6 (obtained by reacting (F 8 -TPP)Fe-Cl with AgPF 6 ), the trinuclear compound [(F 8 -TPP)Fe III -(CN) 2 -{Cu II (TMPA)} 2 ](PF 6 ) 3 ( 6-(PF 6 ) 3 ) is obtained in high yield (94%) (eq 2 and Scheme ). Although 5-coordinate monocyano Mn(III) porphyrins have been reported and a monocyano Fe(III) porphyrin species has been investigated in solution and suggested to exist in certain systems, we note that in the present case a monocyano-bridged (5-coordinate iron) binuclear Fe−Cu product was not observed even when a 1:1 reaction stoichiometry was imposed (i.e., in eq 2); rather, again the trinuclear product 6 was obtained in large quantities.…”

Section: Resultsmentioning

confidence: 99%

Synthesis, Structure, and Solution NMR Studies of Cyanide−Copper(II) and Cyanide-Bridged Iron(III)−Copper(II) Complexes

et al. 1999

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A range of small molecules, such as cyanide, are known to bind and/or inhibit the active site of the heme-copper oxidase enzymes. As such, model studies are aimed at elucidating ligand binding modes and their subsequent impact on spectroscopic properties of derived complexes. We describe here the isolation and characterization of two compounds containing the Fe-CN-Cu moiety, [(py)(F(8)-TPP)Fe(III)-CN-Cu(II)(TMPA)](2+) (5) and [(F(8)-TPP)Fe(III)-(CN)(2)-{Cu(II)(TMPA)}(2)](3+) (6) [py = pyridine, TMPA = tris(2-pyridylmethyl)amine, and (F(8)-TPP) = tetrakis(2,6-difluorophenyl)porphyrinate(2-)]. [Cu(II)(TMPA)(CH(3)CN)](ClO(4))(2) and [(py)(F(8)-TPP)Fe(III)(CN)] (3) react to yield 5, while 6 is formed by combination of [Cu(II)(TMPA)(CN)]PF(6) (2-(PF(6))) and [(F(8)-TPP)Fe(III)(PF(6))] (4). Complex 2-(PF(6)) crystallizes in the orthorhombic space group Iba2 with a = 17.2269(5) Å, b = 17.3143(4) Å, and c = 14.4971(4) Å, Z = 8, complex (5-(Sb/P)F(6))(1.5)(ClO(4))(0.5) was obtained in the orthorhombic space group P222 with a = 17.9541(2) Å, b = 20.5359(1) Å, and c = 21.2023(2) Å, Z = 4, and 6-(PF(6))(3) crystallized in the monoclinic space group P2(1)/c with a = 15.318(4) Å, b = 33.921(2) Å, and c = 19.649(6) Å, beta = 109.69(2) degrees, and Z = 4. Compound 5 possesses a low-spin iron(III) center, bridged via cyanide to copper. The iron-cyanide vector deviates slightly from linearity (174.6(5) degrees ). The copper(II) ion is five-coordinated by the TMPA N-donor atoms and the cyanide carbon atom. The Cu(TMPA) moiety is bent with an angle of 163.8(5) degrees around the cyanide-copper vector. Compound 6 possesses a low-spin iron(III) atom axially coordinated by two cyanide ligands capped on either side by trigonally coordinated [Cu(TMPA)] moieties. The [Cu(1)(TMPA)] unit is twisted somewhat ( angleCu1-N&tbd1;C = 168 degrees ), whereas the [Cu(2)(TMPA)] unit is coordinated in a nearly linear fashion with respect to the cyanide-iron vector ( angleCu2-N&tbd1;C4 = 175 degrees ). (1)H and (2)H NMR spectroscopy on 5 and 6 confirmed the low-spin nature of these iron complexes (pyrrole resonance found at -11.1 and -8 ppm, respectively). The NMR data as well as observed solution magnetic moment (&mgr;(B) = 2.7 for 5; &mgr;(B) = 3.4 for 6) suggest ferromagnetic coupling between the paramagnetic metal ions. This gives rise to an enhancement of the electronic relaxation rate for Cu(II) in both 5 and 6 allowing for the observation of the sharp and downfield shifted TMPA ligand proton signals.

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Section: Resultsmentioning

confidence: 99%

Synthesis, Structure, and Solution NMR Studies of Cyanide−Copper(II) and Cyanide-Bridged Iron(III)−Copper(II) Complexes

et al. 1999

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“…In our case, the primary assignment could be made on the basis of the chemical shift positions of the resonances, their intensities, and their multiplet structure due to J -coupling. A two-dimensional COSY experiment has been shown to be effective in connecting pyrrole proton resonances in iron(III) complexes of tetraarylporphyrins. ,, Two insets in Figure present the COSY maps of [(QTPP)Fe III (CN) 2 ] - . A cross-peak identifies scalar coupling between protons located on the same pyrrole ring.…”

Section: Resultsmentioning

confidence: 99%

“…1 H NMR spectroscopy of paramagnetic hemoproteins and iron porphyrins provides a particularly useful and sensitive tool for determination of the electronic ground states of the iron . In the group of low-spin iron(III) porphyrins, 1 H NMR data have been reported for the following type of axial ligands: pyridine derivatives, 3a, alkyl isocyanide (R-NC), 3c, dimethyl phenylphosphonite (P(OMe) 2 Ph), alkyl (R), aryl (Ar), trialkylphosphine (PR 3 ), imidazoles, , cyanide (CN - ), ,, ammonia, [Si(CH 3 ) 3 ] - , and azaferrocene (η 5 -C 4 H 4 N)(η 5 -C 5 H 5 )Fe …”

Section: Introductionmentioning

confidence: 99%

Characterization of High-Spin and Low-Spin Iron(III) Quinoxalinotetraphenylporphyrin

1997

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The 1H NMR spectra of iron(III) quinoxalinotetraphenylporphyrin ((QTPP)FeIIIX n ), iron(III) (methylquinoxalino)tetraphenylporphyrin ((MQTPP)FeIIIX n ), and iron(III) pyrazinotetraphenylporphyrin ((PTPP)FeIIIX n ) have been studied to elucidate the impact of an aromatic extension of a single pyrrole ring on the electronic structure of the corresponding high- and low-spin iron(III) porphyrins. The 1H NMR spectra of the complexes with the following axial ligands have been reported: chloride, iodide, cyanide, pyridine-d 5 (py-d 5), 4-aminopyridine (4-NH2py), and imidazole (ImH). Modification of the tetraphenylporphyrin by addition of the quinoxaline (pyrazine) fragment results in stabilization of the rare low-spin iron(III) (d xz d yz )4(d xy )1 electronic ground state in the presence of axial cyanide or pyridine ligands. The more common (d xy )2(d xz d yz )3 electronic ground state has been established for [(QTPP)FeIII(4-NH2py)2]+ and [(QTPP)FeIII(ImH)2]+ species. To account for the substituent contribution, the Hückel linear combination of atomic orbitals (LCAO) method has been used to determine the molecular orbitals involved in the spin density delocalization. The deviation from Curie law observed for [(QTPP)FeIII(CN)2]- suggests Boltzmann equilibrium {(d xz )2(d yz )2(d xy )2(Ψ- 1)1 ↔ (d xz )2(d yz )2(d xy )1(Ψ- 1)2} ⇌ (d xz )1(d yz )2(d xy )2(Ψ- 1)2 ⇌ (d xz )2(d yz )1(d xy )2(Ψ- 1)2 where Ψ- 1 is related to the a2u orbital of a regular porphyrin. For the first time in the group of low-spin iron(III) tetraarylporphyrins, the sign reversal of the isotropic shift was directly observed for pyrrole-proton resonances. The structure of (QTPP)FeIIICl was determined by X-ray crystallography. (QTPP)FeIIICl crystallizes in the monoclinic space group P21/c with a = 18.016(5) Å, b = 11.399(3) Å, c = 21.996(5) Å, β = 112.22(5)°, and Z = 4. The refinement of 548 parameters and 2696 reflections yields R 1 = 0.0654, R w2 = 0.1717. The (QTPP)FeIIICl presents features of the high-spin five-coordinate iron(III) tetraphenylporphyrin. The quinoxalinotetraphenylporphyrin macrocycle assumes a saddle-shape geometry.

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“…The full assignment required an application of two-dimensional 1 H NMR techniques. Two-dimensional COSY and NOESY experiments have been shown to be effective in connecting pyrrole proton resonances in low-spin iron(III) complexes of meso -substituted tetraphenylporphyrins. , Within each non-equivalent pyrrole ring the pyrrole protons are expected to be scalar coupled with an approximate 5 Hz coupling constant . Figure presents the COSY spectrum for the representative low-spin β-substituted iron(III) complex, i.e., [(2-Br-TPP)Fe III (CN) 2 ] - .…”

Section: Resultsmentioning

confidence: 99%

“…In systematic studies Walker et al have established that electronic effects controlled by substitution of meso phenyls plays an important role in determining the spin density distribution of low-spin meso substituted iron(III) tetraphenylporphyrins. ,6e,,, In particular, the considerable differentiation of spin densities at the pyrrole-H protons within each pyrrole ring has been demonstrated. ,,, …”

Section: Introductionmentioning

confidence: 99%

NMR Investigation of β-Substituted High-Spin and Low-Spin Iron(III) Tetraphenylporphyrins

et al. 1996

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The NMR spectra of a series of beta-substituted iron(III) tetraphenylporphyrin (2-X-TPP) complexes have been studied to elucidate the relationship between the electron donating/withdrawing properties of the 2-substituent and the (1)H NMR spectral pattern. The electronic nature of the substituent has been significantly varied and covered the -0.6 to 0.8 Hammett constant range. Both high-spin and low-spin complexes of the general formula (2-X-TPP)Fe(III)Cl and [(2-X-TPP)Fe(III)(CN)(2)](-) have been investigated. The (1)H NMR data for the following substituents (X) have been reported: py(+), NO(2), CN, CH(3), BzO (C(6)H(5)COO), H, D, Br, Cl, CH(3), NH(2), NH(3)(+), NHCH(3), OH, and O(-). The (1)H NMR resonances for low-spin dicyano complexes have been completely assigned by a combination of two-dimensional COSY and NOESY experiments. In the case of selected high-spin complexes, the 3-H resonance has been identified by the selective deuteration of all but the 3-H position. The pattern of unambiguously assigned seven pyrrole resonances reflects the asymmetry imposed by 2-substitution and has been used as an unique (1)H NMR spectroscopic probe to map the spin density distribution. The pyrrole isotropic shifts of [(2-X-TPP)Fe(III)(CN)(2)](-) are dominated by the contact term. In order to quantify the substituent effect, the dependence of isotropic shift of all low-spin pyrrole resonances and 3-H high-spin pyrrole resonance versus Hammett constants has been studied. The electronic effect is strongly localized at the beta-substituted pyrrole. The major change of the isotropic shift has also been noted for only one of two adjacent pyrrole rings, i.e., at 7-H and 8-H positions. These neighboring protons, located on a single pyrrole ring, experienced opposite shift changes when electron withdrawing/donating properties were modified. Two other pyrrole rings for all investigated derivatives revealed considerably smaller, substituent related, isotropic shift changes. A long-range secondary isotopic shift has been observed for [(2-D-TPP)Fe(III)(CN)(2)](-). The effect is consistent with a general spin density distribution mechanism due to beta-substitution. A fairly good correlation between the 3-H isotropic shift of (2-X-TPP)Fe(III)Cl and the Hammett constant has been found as well. The observed contact shift pattern of [(2-X-TPP)Fe(III)(CN)(2)](-) reflects spin pi delocalization into the highest filled MO equivalent to the unsubstituted porphyrin 3e(pi) orbital. To account for the substituent contribution, the semiquantitative Fenske-Hall LCAO method has been used to determine the molecular orbitals involved in the spin density delocalization. For low-spin complexes, (13)C pyrrole resonances of carbons bearing a proton have been identified by means of a (1)H-(13)C HMQC experiment. The reversed order of (13)C resonance patterns as compared to their (1)H NMR counterparts has been determined, e.g., the largest isotropic shift of 3-H has been accompanied by the smallest measured (13)C isotropic shift. Analysis of the isotropic shif...

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Cyanide Coordination to Iron(III) Porphyrins and Covalently Linked Diiron(III) Diporphyrins

Cited by 16 publications

References 4 publications

Synthesis, Structure, and Solution NMR Studies of Cyanide−Copper(II) and Cyanide-Bridged Iron(III)−Copper(II) Complexes

Synthesis, Structure, and Solution NMR Studies of Cyanide−Copper(II) and Cyanide-Bridged Iron(III)−Copper(II) Complexes

Characterization of High-Spin and Low-Spin Iron(III) Quinoxalinotetraphenylporphyrin

NMR Investigation of β-Substituted High-Spin and Low-Spin Iron(III) Tetraphenylporphyrins

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