Proton and carbon-13 NMR study of the effects of meso substituents on the S = 3/2, 5/2 spin state admixture of (perchlorato)(tetraarylporphinato)iron(III) complexes

Toney, G. E.; Gold, Avram; Savrin, J. E.; Haar, Leonard W. ter; Sangaiah, R.; Hatfield, William E.

doi:10.1021/ic00193a048

Cited by 28 publications

(27 citation statements)

References 1 publication

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“…For our experiments, we chose the readily available Fe(III) tetraphenylporphyrin perchlorate (FeTPPClO 4 ) as the base porphyrin, and photoswitchable azopyridines as axial ligands (photodissociable ligands, PDLs). FeTPPClO 4 is admixed-spin ( S = 3 / 2 , 5 / 2 ) in non-coordinating and weakly coordinating solvents 11 , 22 – 24 , and very sensitive towards water and oxygen 25 . In acetone, a 6-coordinate complex (Fig.…”

Section: Resultsmentioning

confidence: 99%

Light-controlled switching of the spin state of iron(III)

et al. 2018

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Controlled switching of the spin state of transition metal ions, particularly of FeII and FeIII, is a prerequisite to achieve selectivity, efficiency, and catalysis in a number of metalloenzymes. Here we report on an iron(III) porphyrin with a photochromic axial ligand which, upon irradiation with two different wavelengths reversibly switches its spin state between low-spin (S = 1/2) and high-spin (S = 5/2) in solution (DMSO-acetone, 2:598). The switching efficiency is 76% at room temperature. The system is neither oxygen nor water sensitive, and no fatigue was observed after more than 1000 switching cycles. Concomitant with the spin-flip is a change in redox potential by ~60 mV. Besides serving as a simple model for the first step of the cytochrome P450 catalytic cycle, the spin switch can be used to switch the spin-lattice relaxation time T1 of the water protons by a factor of 15.

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Section: Resultsmentioning

confidence: 99%

Light-controlled switching of the spin state of iron(III)

et al. 2018

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“…The degree and mode of transmission of electronic effects between various points on the porphyrin ring and the central metal via the σ and π orbitals of the four porphyrin nitrogens have long been of interest to those who have investigated the physical properties and chemical reactions of metalloporphyrinates. − Because of the high aromaticity of the porphyrin ring system, electron-donating or -withdrawing substituents on the periphery of the molecule have been shown to affect the basicity of the porphyrin nitrogens, , the rate of N−H tautomerism in porphyrin free-bases, 6b,21a, the chemical shifts of pyrrole and NH protons in free-base tetraphenylporphyrins, 20a, rates of phenyl ring rotation 21b,c,25 and porphyrin ring inversion 22 in metalloporphyrinates, visible absorption spectra,19b spin states, EPR parameters, NMR isotropic shifts, 20b,c,, metal nucleus NMR chemical shifts, , rate 7d,12b and equilibrium 7e-15 constants for axial ligation, reduction potentials 7b,c,8d,11,15-18 of both porphyrin ring and metal redox reactions, and metal incorporation rates. 7f,g, In most of the systems studied (except refs , , , c, and 29), symmetrically substituted tetraphenylporphyrins having either meta or para substituents on the phenyl rings have been investigated, and it has usually been found that the above physical properties correlate with the Hammet σ constants of the substituents: Here P(X) and P(H) are the observed physical property of the tetraphe...…”

Section: Introductionmentioning

confidence: 99%

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

et al. 1998

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To obtain a better understanding of the effects of ortho-halogen and related substituents on the phenyl rings of TPPH2 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 1H NMR spectroscopy. The resonance of the pyrrole protons closest to the phenyl ring bearing the ortho substituent, Ha, 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 2,6-substitution has a similar effect as 2-substitution suggests that size effects are more important than through-bond electronic effects. Equilibrium constants, β2 III, for addition of N-methylimidazole to the series of complexes (o-X)(p-OCH3)3(TPP)FeCl and (2,6-X2)(p-OCH3)3(TPP)FeCl were measured in chloroform at 25 °C. log(β2 III) increases in the order F < Cl < Br < I < F2 < CF3 < Cl2 < Br2, and all β2 III values for mixed substituent porphyrins except the monofluoro-containing complex are larger than the β2 III for the reaction between the symmetrical non-ortho-substituted parent compound, (p-OCH3)4(TPP)FeCl, and NMeIm. Hence, ortho-halogen and -CF3 substituents increase the values of β2 III in order of increasing size, with the 2,6-disubstituted phenyls causing an increase of β2 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(β2 III) is observed (F > CF3 > Cl2 ≫ p-OCH3). Both sets of equilibrium constant data suggest that ortho-halogens and -CF3 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 Cl- to dissociate from the Fe+Cl- starting material in CHCl3 and making the complex less stable; the former contribution is more important in CHCl3, while the latter becomes evident in DMF. The 1H 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 Cl2 > F2 > Br2 ≫ F > Cl > Br ∼ CF3 ≫ 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(β2 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(β2 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 el...

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“…[7][8][9][10] For planar porphyrin ligands, such as high-spin FeTPPCl (or FeOEPCl), the meso-C signal appears at a downfield position of 500 ppm (or 380 ppm), and 368 ppm (or 246 ppm) for the admixed (5/2, 3/2) FeTPPClO 4 (or FeOEPClO 4 ), respectively (see Table 1; TPP = dianion of 5,10,15,20-tetraphenylporphyrin and OEP = dianion of 2,3,7,8,12,13,17,18-octaethylporphyrin). [11,12] These downfield shifts at the meso-C atoms have been attributed by Cheng et al to interactions between the iron(III) d z 2 and the porphyrin a 2u orbitals. [13] However, for saddled porphyrin ligands, considering the main skeleton of the macrocycle, the five-coordinate saddleshaped Fe(OETPP)Cl has a local C 2v symmetry, which is lower than the C 4v symmetry of five-coordinate planar iron(III) porphyrin complexes.…”

Section: In Memory Of Ru-jen Chengmentioning

confidence: 81%

“…Fe(TPP)X [7,11,12,14] porphyrin complexes in similar spin states so far, but this change has been postulated because of the difference in the geometric structures. [7] In this study, we employed density functional theory (DFT) calculations to correlate the Fe-porphyrin bonding interactions with calculated spin populations, including the total spin, the localized p spin, and the Fermi contact spin densities on the porphyrin macrocycle to elucidate these unexpected NMR data.…”

Section: In Memory Of Ru-jen Chengmentioning

confidence: 99%

Paramagnetic NMR Shifts for Saddle‐Shaped Five‐Coordinate Iron(III) Porphyrin Complexes with Intermediate‐Spin Structure

Chen

2012

Angew Chem Int Ed

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Calculable results: Complex density functional calculations and spin distribution analyses have been performed for planar and saddled iron(III) porphyrin complexes (see picture). The spin populations and the extent of the interactions between the metal and the porphyrin orbitals were determined, which can explain the large change of meso-carbon atom chemical shifts observed for different porphyrin ligands

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Proton and carbon-13 NMR study of the effects of meso substituents on the S = 3/2, 5/2 spin state admixture of (perchlorato)(tetraarylporphinato)iron(III) complexes

Cited by 28 publications

References 1 publication

Light-controlled switching of the spin state of iron(III)

Light-controlled switching of the spin state of iron(III)

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

Paramagnetic NMR Shifts for Saddle‐Shaped Five‐Coordinate Iron(III) Porphyrin Complexes with Intermediate‐Spin Structure

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