The Binding Ability of Iron Bonded to Porphodimethene: Structural, Magnetic, and Electronic Relationship to Iron Porphyrin Complexes (original) (raw)

Electronic Effects in Transition Metal Porphyrins. 9. Effect of Phenyl Ortho Substituents on the Spectroscopic and Redox Properties and Axial Ligand Binding Constants of Iron(III) Tetraphenylporphyrinates

Inorganic Chemistry, 1998

To obtain a better understanding of the effects of ortho-halogen and related substituents on the phenyl rings of TPPH 2 and (TPP)Fe(III) complexes, a series of unsymmetrically substituted tetraphenylporphyrins have been synthesized. In each of these complexes one phenyl ring bears halogen(s) on one (or both) ortho position(s), while the other three phenyl rings carry para-methoxy substituents. The free-base porphyrins were characterized by UV-visible and 1 H NMR spectroscopy. The resonance of the pyrrole protons closest to the phenyl ring bearing the ortho substituent, H a , of the free-base porphyrins shows a progressive shift to higher shielding as the atomic radius and Hammett substituent constant σ p of the substituent increases. However, the fact that 2,6substitution has a similar effect as 2-substitution suggests that size effects are more important than through-bond electronic effects. Equilibrium constants, 2 III , for addition of N-methylimidazole to the series of complexes (o-X)(p-OCH 3 ) 3 (TPP)FeCl and (2,6-X 2 )(p-OCH 3 ) 3 (TPP)FeCl were measured in chloroform at 25°C. log( 2 III ) increases in the order F < Cl < Br < I < F 2 < CF 3 < Cl 2 < Br 2 , and all 2 III values for mixed substituent porphyrins except the monofluoro-containing complex are larger than the 2 III for the reaction between the symmetrical non-ortho-substituted parent compound, (p-OCH 3 ) 4 (TPP)FeCl, and NMeIm. Hence, ortho-halogen and -CF 3 substituents increase the values of 2 III in order of increasing size, with the 2,6-disubstituted phenyls causing an increase of 2 III by more than a factor of 2 over that for 2-substituted phenyls. In the strongly solvating solvent dimethylformamide, where dissociation of the anion has already taken place, the opposite order of log-( 2 III ) is observed (F > CF 3 > Cl 2 . p-OCH 3 ). Both sets of equilibrium constant data suggest that orthohalogens and -CF 3 groups are electron donating, which we believe is due to direct overlap between the electron clouds of the halogens and the π system of the porphyrin. This direct overlap of electron clouds decreases the Lewis acidity of Fe(III), both making it easier for Clto dissociate from the Fe + Clstarting material in CHCl 3 and making the complex less stable; the former contribution is more important in CHCl 3 , while the latter becomes evident in DMF. The 1 H NMR spectra of the same series of low-spin Fe(III) complexes show a decrease in the spread of the pyrrole-H resonances in the order of Cl 2 > F 2 > Br 2 . F > Cl > Br ∼ CF 3 . I. This order suggests that the apparent electron-donating characteristics of the substituents decrease in the listed order, which is quite different from that derived from the values of log( 2 III ) measured in chloroform solution. The differences probably result from the fact that these two physical properties are sensing different effects of the ortho substituents: log( 2 III ) values probe changes in the σ basicity of the pyrrole nitrogens and hence the Lewis acidity of the metal, while the spread of pyrrole-H resonances probes changes in the π electron density distribution in the e(π) orbitals and/or differences in the energy separation of those two orbitals of the porphyrin ring.

Iron Porphyrin Chemistry

Encyclopedia of Inorganic Chemistry, 2006

Possible oxidation and spin states of iron porphyrins and the d orbital configurations expected in each case. All of these states (excluding high-spin d 7 , which is not included in the figure) have been observed for iron porphyrins, and are discussed in this article. In addition, the spin-admixed S = 3/2,5/2 state of Fe III and the alternative orbital configuration for low-spin Fe III , with d xy higher in energy than d xz ,d yz , are also discussed

X-ray photoelectron spectroscopic studies on monomeric and dimeric iron porphyrins

Journal of the American Chemical Society, 1980

The Fe 2~312 and N 1s X-ray PES binding energies for the dimeric iron porphyrin complexes p-nitrido-bis[a,P,y,6-tetraphenylporphinatoiron] and p-oxo-bis[a,P,y,G-tetraphenylporphinatoiron] are reported. In addition, X-ray PES binding energies for the monomeric a,P,y,&tetraphenylporphinatoiron cation with selected anions (C104-, Br-, CI-, and N3-) are found to be correlated with the half-wave potentials for reduction in the noncoordinating solvent dichloromethane. Comparisons are made between the previously reported infrared, Mossbauer, X-ray crystallographic, magnetic susceptibility, and electrochemical results and the X-ray PES data in an attempt to unambiguously assign the electron environment of the p-nitrido complex. In contrast to the p-oxo dimer and the monomers, the electronic configuration about each five-coordinate Fe atom in the p-nitrido dimer has been shown to be low spin.

Structural, Conformational, and Spectroscopic Studies of Primary Amine Complexes of Iron(II) Porphyrins

Inorganic Chemistry, 1999

Three novel bis(primary amine)iron(II) porphyrins [Fe(TPP)(RNH 2) 2 ], where RNH 2) 1-butylamine, benzylamine, and phenethylamine, have been synthesized and characterized by X-ray crystallography and IR, electronic, and Mössbauer spectroscopy. The compounds provide unprecedented structural data for the coordination of primary amines by iron(II) porphyrins. The Fe-N ax distances of [Fe(TPP)(1-BuNH 2) 2 ], [Fe(TPP)(BzNH 2) 2 ], and [Fe-(TPP)(PhCH 2 CH 2 NH 2) 2 ] are 2.039(3), 2.043(3), and 2.028(2) Å, respectively. The Fe-N p distances of the three complexes average 1.990(2) Å. The zero-field Mössbauer spectra (5-300 K) show comparable isomer shifts (0.393(1)-0.493(1) mm/s) and quadrupole splittings (1.144(6)-1.204(3) mm/s) that are consistent with an S) 0 iron(II) assignment in each case. The bis(primary amine) complexes are structurally and spectroscopically similar to [Fe(TPP)(Py) 2 ] derivatives, where Py) an unsubstituted pyridine. Molecular mechanics (MM) calculations with a force field parametrized for primary and secondary amine complexes of iron(II) porphyrins show that stable conformations arise when the R-CH 2 and NH 2 protons of the coordinated ligands are staggered relative to the Fe-N p bonds of the porphyrin core. The lowest energy conformations of the three [Fe(TPP)(RNH 2) 2 ] complexes therefore have the ligand R-carbons positioned directly over the Fe-N p bonds of the porphyrin core. The X-ray structure of [Fe(TPP)(PhCH 2 CH 2 NH 2) 2 ] lies close to the global minimum (φ 1 , φ 2) 0, 180°) on the potential surface, while [Fe(TPP)(BzNH 2) 2 ] and [Fe(TPP)(1-BuNH 2) 2 ] show deviations that may be attributed to packing interactions in the solid and intrinsically low barriers to axial ligand rotation (<0.5 kcal/mol). Three types of minimum energy conformation are accessible for [Fe(TPP)(Pip) 2 ]. The lowest energy conformation has an S 4ruffled porphyrin core. The conformation which matches the X-ray structure (Radonovich, L.

Effect of meso substituents on exchange-coupling interactions in .mu.-oxo iron(III) porphyrin dimers

Inorganic Chemistry, 1986

The p-oxo iron(II1) porphyrin dimers [(TPP)Fe],O, [(TPP(COCH,))Fe],O, [(TPP(4-CF3))FeI20, and [(TPP(F5))FeI2O (where TPP is meso-tetraphenylporphyrin, TPP(4-OCH3) is meso-tetrakis(4-methoxyphenyl)porphyrin, TPP(4-CF3) is meso-tetrakis-(4-(trifluoromethyl)phenyl)porphyrin, and TPP(F5) is meso-tetrakis(pentafluorophenyl)porphyrin) have been studied to determine the effect of peripheral substituents on the porphyrin rings on properties of the molecules. Variable-temperature magnetic susceptibility studies on solid samples yielded the following exchange-coupling constants for the antiferromagnetically coupled iron(II1) ions:-146.8 cm-I, [(TPP(4-OCH3))FeI2O-135.7 cm-I, [(TPP)Fe],O;-136.4 c d , [(TPP(4-CF3))Fe],0;-146.9 cm-I, [ (TPP(F,))Fe],O. Variable-temperature I3C NMR studies of dichloromethane solutions yield exchange-coupling constants of-150 cm-' for [(TPP(4-OCH3))Fe],O,-145 cm-' for [(TPP)FeI20, and-129 cm-' for [(TPP(F,))Fe],O. Raman spectra were collected in the region of the energy of the outer-ring stretching modes found at approximately 1560 cm-I. The position of this band is empirically related to the porphyrin core size, and the data indicate that the porphyrin center-pyrrole nitrogen (C,-N) distances increase in the order [(TPP(FS))FeI20 < [(TPP(4-CF3))FeI2O < [(TPP)FeI20 < [(TPP(4-OCH3))FeI20. The data support the hypothesis that the porphyrin ring core size increases as the electron-releasing capability of the peripheral substituent increases. For the para-substituted complexes, increasing core size correlates with stronger axial binding, reflected in stronger antiferromagnetic coupling. The anomalous behavior of [(TPP(F,))Fe],O may result from distortions caused by steric interactions of the o-fluorines.

Electronic Structures of Five-Coordinate Iron(III) Porphyrin Complexes with Highly Ruffled Porphyrin Ring

Inorganic Chemistry, 2004

The spin states of the iron(III) complexes with a highly ruffled porphyrin ring, [Fe(TEtPrP)X] where X ) F -, Cl -, Br -, I -, and ClO 4 -, have been examined by 1 H NMR, 13 C NMR, EPR, and Mössbauer spectroscopy. While the F -, Cl -, and Brcomplexes adopt a high-spin (S ) 5 / 2 ) state, the Icomplex exhibits an admixed intermediate-spin (S ) 5 / 2 , 3 / 2 ) state in CD 2 Cl 2 solution. The Icomplex shows, however, a quite pure high-spin state in toluene solution as well as in the solid. The results contrast those of highly saddled [Fe(OETPP)X] where the Icomplex exhibits an essentially pure intermediate-spin state both in solution and in the solid. In contrast to the halide-ligated complexes, the ClO 4complex shows a quite pure intermediate-spin state. The 13 C NMR spectra of [Fe(TEtPrP)-ClO 4 ] are characterized by the downfield and upfield shifts of the meso and pyrrole-R carbon signals, respectively: δ(meso) ) +342 and δ(R-py) ) −287 ppm at 298 K. The data indicate that the meso carbon atoms of [Fe-(TEtPrP)ClO 4 ] have considerable amounts of positive spin, which in turn indicate that the iron has an unpaired electron in the d xy orbital; the unpaired electron in the d xy orbital is delocalized to the meso positions due to the iron(d xy )−porphyrin(a 2u ) interaction. Similar results have been obtained in analogous [Fe(T i PrP)X] though the intermediate-spin character of [Fe(T i PrP)X] is much larger than that of the corresponding [Fe(TEtPrP)X]. On the basis of these results, we have concluded that the highly ruffled intermediate-spin complexes such as [Fe(TEtPrP)-ClO 4 ] and [Fe(T i PrP)ClO 4 ] adopt a novel (d xz , d yz ) 3 (d xy ) 1 (d z 2 ) 1 electron configuration; the electron configuration of the intermediate-spin complexes reported previously is believed to be (d xy ) 2 (d xz , d yz ) 2 (d z 2 ) 1 . Neya, S.; Ikeue, T.; Takahashi, M.; Takeda, M.; Funasaki, N.; Nakamura, M. Inorg Chem. 2002, 41, 4627-4629. (9) Ikeue, T.; Ohgo, Y.; Takahashi, M.; Takeda, M.; Neya, S.; Funasaki, N.; Nakamura, M. Scheme 3. Schematic Representation of the Change in Energy Levels of the Iron d Orbitals in Ruffled [Fe(TRP)X] and Saddled [Fe(OETPP)X]

Effect of Meso Substituents on Exchange-Coupling Interactions in μ-Oxo Iron(III) Porphyrin Dimers

1986

Structural, Electrochemical, and Spectroscopic Properties of a Class of Dodecasubstituted Iron Porphyrins Bearing Four Positive Charges Close to the Metal

European Journal of Inorganic Chemistry, 2007

The first iron complexes of the tetracationic 2, 3,7,8,12,13,17,18octaethyl-5,10,15,20-tetra-N-pyridiniumylporphyrin, (OE-Py 4 P) 4+ , in which four pyridine molecules are attached to the meso-carbon atoms through their nitrogen atoms, were synthesized in three steps starting from Zn(OEP) (Zn-β-octaethylporphyrin) with an overall yield of ca. 30 %. The X-ray structure of [Fe II (OEPy 4 P)(pyridine) 2 ](CF 3 SO 3 ) 3 (Br) established that the molecule adopts a severely distorted nonplanar saddle conformation. 1 H NMR spectroscopy showed that the [Fe II (OEPy 4 P)(B) 2 ] 4+ ligated complexes, B = pyridine (Py) or imidazole (Im), are low-spin, Fe II , S = 0. These complexes exhibit redox potentials for the Fe III /Fe II couple that range between 0.62 and 0.38 V (vs. Ag/AgCl) and are shifted by as much as +0.7 V relative to those of the corresponding [a] Condensed Matter Materials and Methods: Methanol (MeOH), diethyl ether (Et 2 O) and Celite 545 were purchased from SDS and used without further www.eurjic.org 7 be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data\_request/cif.

Durene-capped porphyrin complexes of iron(II)

Journal of Inorganic Biochemistry, 1986

Solution equilibria are presented for in situ reactions of the type FeIl(porp) + B ;::' : FeIl(porp)B, where porp represents the dianion of some durene-capped porphyrins with variable length linking methylene straps, and B is I-methyl, 1,2-dimethyl, or 1,5-dicyclohexylimidazole. Increasing distortion of the porphyrin skeleton has no effect on coordination of B at the unhindered side of the capped porphyrin. Increasing skeleton distortion gives rise to regular trends within the visible spectra of the free base porphyrins, the hemin (Felli) chlorides, and six-coordinate FeII(porp)B(L) species (L = RNC, CO, O2), while the visible spectra of FeII(porp) and of FeII(porp)B species are independent of the nature of porp and B, which may be related to greater flexibility of the lower coordination number systems. v(CO) data for the FeII(porp)(CO)B species are discussed briefly.

The Binding Ability of Iron Bonded to Porphodimethene: Structural, Magnetic, and Electronic Relationship to Iron Porphyrin Complexes (original) (raw)

Related papers