Application of carbon-13 NMR spectroscopy for measurement of antiferromagnetic coupling in μ-oxo iron(III) porphyrin dimers

Boersma, Arden D.; Phillippi, Martin A.; Goff, Harold M.

doi:10.1016/0022-2364(84)90119-7

Cited by 3 publications

(3 citation statements)

References 12 publications

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“…Complexes displaying strong antiferromagnetic coupling between two or more transition metal centers often manifest chemical shift temperature dependencies . Observation by NMR spectroscopy does not require analytically pure material and is relatively insensitive to paramagnetic impurities, because it probes local magnetic effects . Since H 2 loss from [(silox) 2 W] 2 (μ-H) 4 ( 7 ) prevents its isolation as a solid and equilibrium amounts of 3 are always present, NMR analysis presents obvious advantages to bulk susceptibility measurements.…”

Section: Discussionmentioning

confidence: 99%

Ditungsten Siloxide Hydrides, [(silox)₂WH_n]₂(n= 1, 2; silox =^tBuSiO), and Related Complexes

et al. 1996

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The addition of 4.0 equiv of Na(silox) to Na[W(2)Cl(7)(THF)(5)] afforded (silox)(2)ClW&tbd1;WCl(silox)(2) (1, 65%). Treatment of 1 with 2.0 equiv of MeMgBr in Et(2)O provided (silox)(2)MeW&tbd1;WMe(silox)(2) (2, 81%). In the presence of 1 atm of H(2), reduction of 1 with 2.0 equiv of Na/Hg in DME provided (silox)(2)HW&tbd1;WH(silox)(2) (3, 70%), characterized by a hydride resonance at delta 19.69 (J(WH) = 325 Hz, (1)H NMR). Exposure of 2 to 1 atm of H(2) yielded 3 and CH(4) via (silox)(2)HW&tbd1;WMe(silox)(2) (4); use of D(2) led to [(silox)(2)WD](2) (3-d(2)). Exposure of 3 to ethylene ( approximately 1 atm, 25 degrees C) in hexanes generated (silox)(2)EtW&tbd1;WEt(silox)(2) (5), but solutions of 5 reverted to 3 and free C(2)H(4) upon standing. NMR spectral data are consistent with a sterically locked, gauche, C(2) symmetry for 1-5. Thermolysis of 3 at 100 degrees C (4 h) resulted in partial conversion to (silox)(2)HW&tbd1;W(OSi(t)Bu(2)CMe(2)CH(2))(silox) (6a, approximately 60%) and free H(2), while extended thermolysis with degassing (5 d, 70 degrees C) produced a second cyclometalated rotational isomer, 6b (6a:6b approximately 3:1). When left at 25 degrees C (4 h) in sealed NMR tubes, 6 and free H(2) regenerated 3. Reduction of 1 with 2.0 equiv of Na/Hg in DME also afforded 6a (25%). When 3 was exposed to approximately 3 atm of H(2), equilibrium amounts of [(silox)(2)WH(2)](2) (7) were observed by (1)H NMR spectroscopy (3 + H(2) right harpoon over left harpoon 7; 25.9-88.7 degrees C, DeltaH = -9.6(4) kcal/mol, DeltaS = -21(2) eu). Benzene solutions of 3 and 1-3 atm of D(2) revealed incorporation of deuterium into the silox ligands, presumably via intermediate 6. In sealed tubes containing [(silox)(2)WCl](2) (1) and dihydrogen (1-3 atm), (1)H NMR spectral evidence for [(silox)(2)WCl](2)(&mgr;-H)(2) (8) was obtained, suggesting that formation of 3 from 1 proceeded via reduction of 8. Alternatively, 3 may be formed from direct reduction of 1 to give [(silox)(2)W](2) (9), followed by H(2) addition. Hydride chemical shifts for 7 are temperature dependent, varying from delta 1.39 (-70 degrees C, toluene-d(8)), to delta 3.68 (90 degrees C). (29)Si{(1)H} NMR spectra revealed a similar temperature dependence of the silox (delta 12.43, -60 degrees C, to delta 13.64, 45 degrees C) resonances. These effects may arise from thermal population of a low-lying, deltadelta, paramagnetic excited state of D(2)(d)() [(silox)(2)W](2)(&mgr;-H)(4) (DeltaE approximately 2.1 kcal/mol, chi(7a) approximately 0.03), an explanation favored over thermal equilibration with an energetically similar but structurally distinct isomer (e.g., [(silox)(2)WH(2)](2)(&mgr;-H)(2), DeltaG degrees approximately 0.69 kcal/mol, chi(7b) approximately 0.25) on the basis of spectral arguments. Extended Hückel and ab initio molecular orbital calculations on model complexes [(H(3)SiO)(2)W](2)(&mgr;-H)(4) (staggered bridged 7a', EHMO), [(H(3)SiO)(2)WH(2)](2) (all-terminal 7b', EHMO), [(H(3)SiO)(2)W](2) (9', EHMO), (HO)(4)W(2)(H(4)) (staggered-bridged 7", ab initi...

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Section: Discussionmentioning

confidence: 99%

Ditungsten Siloxide Hydrides, [(silox)₂WH_n]₂(n= 1, 2; silox =^tBuSiO), and Related Complexes

et al. 1996

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“…For the mixed-valent iron sites of hemerythrin and uteroferrin, -J values of 10-30 cm-1 have been determined from the temperature dependence of isotropic shifts of ligands to the ferric center.72,73 These values were later verified by other means.69,74 -J values of ~140-150 cm-1 have been determined from the temperature dependence of 13C NMR isotropic shifts of the pyrrole carbons in synthetic diferric oxobridged porphyrin complexes. 75,76 The larger dispersion of 13C signals means that reasonable variations with temperature can be obtained even for such strongly coupled systems. The temperature variation was fit by use of different hyperfine coupling constants for the S = 1 and 2 spin levels.…”

Section: B Methods For Measurement Of -Jmentioning

confidence: 99%

Oxo- and hydroxo-bridged diiron complexes: a chemical perspective on a biological unit

Kurtz¹

1990

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Contents I. Introduction 585 A. Limitations and Scope 585 B. Hydrolysis of Fe(IIIXaq) 586 II. Structure 586 A. Bridging Structural Types 586 1. p-Oxo Category 586 2. /i-Hydroxo Category 587 B. Types of Terminal Ligands and Their 587 Structural Effects III. Synthesis 589 A. General Methods 589 B. Equilibria and Pathways of Formation 589 C. Di-and Tribridged Complexes 590 D. Bridge Substitution and Exchange 591 IV. Electronic Absorption Spectra 591 A. Survey 591 B. (n-Oxo)diiron(111) Complexes 591 1. Oxo Dimer Region 591 2. Lower Energy Bands 593 V. IR and Raman Spectra 594 A. Vibrational Modes 594 B. (/i-OxoXJiiron(111) Complexes 595 VI. Magnetism 596 A. Antiferromagnetism 596 B Methods for Measurement of -J 596 C. Other Types of Spin Coupling 597 D. Orbital Pathways for Spin-Exchange 597 Coupling E. Oxidation Levels Other than Diferric 599 VII. EPR Spectra 599 A. Half-Integer Spin Ground States 599 B. Integer Spin States 599 VIII. Mossbauer Spectra 600 IX. Reactivity 600 A. Electrochemistry 600 B. Oxygen Transfer and 02 Activation 600 X. Some Implications for Diiron Sites in 601 Chemistry and Biology A. "Spontaneous Self-Assembly" of the 601 (g-Oxo)diiron(ni) Unit B. Structural Comparisons with the Diiron Site 601 of Hemerythrin 1. Diferric and Diferrous Forms 601 2. Mixed-Valent Forms 602 C. Comparison of Hemerythrin and Methane 602 Monooxygenase XI. Acknowledgment

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“…These β-H resonances demonstrate the anti-Curie behavior of the isotropic shifts, i.e., an increase of the pyrrole resonance shifts on warming, as expected for µ-oxo-bridged diiron porphyrins. 63 The spectral properties resemble those of asymmetric tetraphenylporphyrin derivatives including µ-oxo-bridged diiron complexes of Nmethylporphyrin, 21-oxaporphyrin, and recently characterized µ-oxo diiron(III) 5,10,15-triphenylporphyrin (6-Fe 2 O) [δ, 13.2 (4H), 13.4 (4H), 13.6 (8H), meso-H (2H) 6.3 ppm, 293 K]. 21,58,64 The ethynyl-H resonance of 1-Fe 2 O is expected in the region of intense solvent signals (1-2 ppm).…”

Section: Synthesis Ofmentioning

confidence: 99%

¹H NMR Investigation of High-Spin and Low-Spin Iron(III) meso-Ethynylporphyrins

2005

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The 1H NMR spectra of iron(III) 5-ethynyl-10,15,20-tri(p-tolyl)porphyrin [(ETrTP)Fe(III)X(n)], iron(III) 5-(phenylethynyl)-10,15,20-tri(p-tolyl)porphyrin [(PETrTP)Fe(III)X(n)], iron(III) 5-(phenylbutadiynyl)-10,15,20-tri(p-tolyl)porphyrin [(PBTrTP)Fe(III)X(n)], iron(III) 5,10,15,20-tetra(phenylethynyl)porphyrin [(TPEP)Fe(III)X(n)], iron(III) 1,4-bis-[10,15,20-tri(p-tolyl)porphyrin-5-yl]-1,3-butadiyne {[(TrTP)Fe(III)X(n)]2 B}, and 5,10,15-triphenylporphyrin [(TrPP)Fe(III)X(n)] have been studied to elucidate the impact of meso-ethynyl substitution on the electronic structure and spin density distribution of high-spin (X = Cl-, n = 1) and low-spin (X = CN-, n = 2) derivatives. The meso substituents, i.e., ethynyl, phenylethynyl, and phenylbutadiynyl, provided insight into the efficiency of spin density delocalization along structural elements that are typically applied to transmit electronic effects along multipart polyporphyrinic systems. The positive spin density localized at the meso-carbon of high-spin iron(III) ethynylporphyrins is effectively delocalized along the ethyne or butadiyne fragment as illustrated by the comparison of isotropic shifts of C(meso)-H and -CC-H determined for (TrPP)Fe(III)Cl (-82.6 ppm, 293 K) and (ETrTP)Fe(III)Cl (-49.5 ppm, 298 K). The replacement of the ethynyl hydrogen by phenyl or phenylethynyl provided evidence for the pi spin density distribution around the introduced phenyl ring. An analysis of the isotropic shifts for the low-spin bis-cyanide iron(III) porphyrins series reveals the analogous mechanism of spin density transfer. Treatment of high-spin [(TrTP)Fe(III)Cl]2 B with a base resulted in formation of the cyclic [(TrTP)Fe(III)OFe(III)(TrTP)B]2 complex linked by two mu-oxo bridges. (TPEP)H2 has been characterized by X-ray crystallography as a porphyrin dication where two molecules of trifluoroacetic acid associate with two coordinated trifluoroacetate anions. The X-ray structure of bis-tetrahydrofuran 1,4-bis[10,15,20-tri(p-tolyl)porphyrinatozinc(II)-5-yl]-1,3-butadiyne complex {[(TrTP)Zn(II)(THF)]2 B} reveals two parallel, non-coplanar [(TrTP)Zn(THF)] subunits linked by the linear butadiyne moiety.

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Application of carbon-13 NMR spectroscopy for measurement of antiferromagnetic coupling in μ-oxo iron(III) porphyrin dimers

Cited by 3 publications

References 12 publications

Ditungsten Siloxide Hydrides, [(silox)₂WH_n]₂(n= 1, 2; silox =^tBuSiO), and Related Complexes

Ditungsten Siloxide Hydrides, [(silox)₂WH_n]₂(n= 1, 2; silox =^tBuSiO), and Related Complexes

Oxo- and hydroxo-bridged diiron complexes: a chemical perspective on a biological unit

¹H NMR Investigation of High-Spin and Low-Spin Iron(III) meso-Ethynylporphyrins

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Application of carbon-13 NMR spectroscopy for measurement of antiferromagnetic coupling in μ-oxo iron(III) porphyrin dimers

Cited by 3 publications

References 12 publications

Ditungsten Siloxide Hydrides, [(silox)2WHn]2(n= 1, 2; silox =tBuSiO), and Related Complexes

Ditungsten Siloxide Hydrides, [(silox)2WHn]2(n= 1, 2; silox =tBuSiO), and Related Complexes

Oxo- and hydroxo-bridged diiron complexes: a chemical perspective on a biological unit

1H NMR Investigation of High-Spin and Low-Spin Iron(III) meso-Ethynylporphyrins

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Ditungsten Siloxide Hydrides, [(silox)₂WH_n]₂(n= 1, 2; silox =^tBuSiO), and Related Complexes

Ditungsten Siloxide Hydrides, [(silox)₂WH_n]₂(n= 1, 2; silox =^tBuSiO), and Related Complexes

¹H NMR Investigation of High-Spin and Low-Spin Iron(III) meso-Ethynylporphyrins