Studies on the proton and carbon-13 contact shifts for .sigma.-bonded molecules. Stereospecific electron spin transmission in cyclic and bicyclic amines

Morishima, Isao; Yoshikawa, Kenichi; Okada, Koji

doi:10.1021/ja00429a009

Cited by 18 publications

(3 citation statements)

References 5 publications

(14 reference statements)

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“…Accordingly the first situation promotes β-spin density transfer where the α-spin transfer is preferred for ls iron(III) due to the (d xy ) 1 electron in the second case. Similar sign reversals have been determined for adamantane bound to low-spin d 5 iron(III) as compared to azaadamantane coordinated to high-spin nickel(II). , …”

Section: Resultssupporting

confidence: 78%

“…Similar sign reversals have been determined for adamantane bound to low-spin d 5 iron(III) as compared to azaadamantane coordinated to high-spin nickel(II). 44,45 Conclusion. Low-spin iron(III) tetracyclohexylporphyrin and iron(III) chiroporphyrin complexes exhibit electronic properties considerably different from those of the analogous low-spin iron(III) tetrarylporphyrins.…”

Section: Methodsmentioning

confidence: 99%

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Stabilization of the Less Common (d_xzd_y_z)⁴(d_x_y)¹Iron(III) Porphyrin Ground Electronic State: ¹H NMR Investigations of Iron(III) 5,10,15,20-Tetracyclohexylporphyrin

et al. 1998

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High-spin and low-spin complexes of the iron(III) tetrakis(meso-cyclohexyl)porphyrin ((TCHP)FeIII) have been studied by means of 1-D and 2-D 1H NMR. The complete assignment of porphyrin and R-imidazole 1H resonances has been done on the basis of 2-D COSY and NOESY techniques as well as by selective deuteration of imidazole. The chemical shifts of pyrrole β-Hs have been used as the probe of the electronic state of an iron(III) metal ion. It has been found that cyanide coordinates to the high-spin (TCHP)FeIIICl complex, leading to the formation of the low-spin [(TCHP)FeIII(CN)2]-, with the rare (d xz d yz )4(d xy )1 ground electronic state (the pyrrole β-H resonance at 12.01 ppm at 293 K in CD3OD). A contribution of two electronic configurations, (d xy )2(d xz d yz )3 and (d xz d yz )4(d xy )1, to the ground state of the metal ion has been invoked for the low-spin [(TCHP)FeIII(R-Im)2]+ complexes. Characteristic 1H NMR shifts for these complexes include the pyrrole resonance at 2.81 ppm accompanied by the markedly upfield shifted imidazole resonances at −19.67 ppm (2-H), −10.58 ppm (4-H), −4.05 ppm (5-H), and 0.97 ppm (1-H). An admixture of a (d xz d yz )4(d xy )1 configuration into the ground electronic state increases in the order imidazole (ImH) < 1-methylimidazole (1-MeIm) < 1,2-dimethylimidazole (1,2-diMeIm), following an enlargement of the axial ligand steric hindrance. The rotation of the 1,2-diMeIm around Fe−N bond in the low-spin [(TCHP)FeIII(1,2-diMeIm)2]+ complex is slow on the 1H NMR time scale even at 293 K. Consequently four β-H resonances and the diastereotopy of the cyclohexyl meso-substituents have been observed. The meso-cyclohexyl groups rotate freely at temperature above 243 K, whereas the frozen rotation below 233 K leads to the formation of additional rotational isomers as demonstrated by multiplicity of β-H resonances for high-spin and low-spin complexes studied.

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Section: Resultssupporting

confidence: 78%

Section: Methodsmentioning

confidence: 99%

Stabilization of the Less Common (d_xzd_y_z)⁴(d_x_y)¹Iron(III) Porphyrin Ground Electronic State: ¹H NMR Investigations of Iron(III) 5,10,15,20-Tetracyclohexylporphyrin

et al. 1998

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“…Similar results are obtained with the isoelectronic neutral hydrocarbon radical [18] with the same conformation at the radical site, defined by the angle 4. On the other hand the model of corresponding anion radicals or hybrids of anion and cation radicals [19] are clearly inconsistent with experimental results.…”

Section: Hyperfine Coupling Constants and Spin Densitiessupporting

confidence: 82%

Hyperfine couplings and ¹³C relaxation in alkylamines coordinated to Ni(II) acetylacetonate

1979

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The conformational dependence of the proton and carbon-13 hyperfine coupling constants in aliphatic amines Coordinated to Ni(AA)~ has been investigated by N.M.R. contact shift measurements. It is shown that the hyperfine coupling constants ac/~ and ari B are given by a~ (O) = px*'(B: cos O+ B~ cos 2 0), with B: H = 10.5 G, B2 H = 10.6 G, B: c = -4.9 G, B~ c = 13.1 G where 0 is the torsion angle about the C1-N bond. The experimental values of aH/~ and ac/~ in the ethylamine-Ni(AA)z complex have been compared with those calculated from the above expression and the potential function computed by INDO for the rotation of C~H5 about the N-C1 bond in EtI~IH~ +. Good agreement is obtained for a potential barrier Vo = 15.5 kJ mol-:.The :3C paramagnetic relaxation rates T:M-: and T2M-: in the complexes have also been determined. For n-butyl and n-hexylamine complexes, the dipolar longitudinal relaxation rates have been calculated from Monte Carlo simulations of random fluctuations of the magnetic field due to internal and overall motions and to electron spin transitions. Satisfactory agreement with experiment has been obtained from C3 to the terminal methyl carbon. On the other hand T:M-: of C1 and C2 are significantly larger than expected from Monte.Carlo calculations because of local 2s and 2p spin densities. The latter contribution has been estimated by calculating the hyperfine dipolar tensor from the average C-Ni distances and the C1 or C2 spin density matrices obtained from INDO calculations on related alkylamine cation radicals. The validity of this semi-quantitative treatment has been checked on the simplest example of the ethylamine-Ni(AA)2 complex.

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Substituent Effects on ¹³ C Chemical Shifts in Aliphatic Molecular Systems. Dependence on Constitution and Stereochemistry

Duddeck¹

1986

Topics in Stereochemistry

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Studies on the proton and carbon-13 contact shifts for .sigma.-bonded molecules. Stereospecific electron spin transmission in cyclic and bicyclic amines

Cited by 18 publications

References 5 publications

Stabilization of the Less Common (d_xzd_y_z)⁴(d_x_y)¹Iron(III) Porphyrin Ground Electronic State: ¹H NMR Investigations of Iron(III) 5,10,15,20-Tetracyclohexylporphyrin

Stabilization of the Less Common (d_xzd_y_z)⁴(d_x_y)¹Iron(III) Porphyrin Ground Electronic State: ¹H NMR Investigations of Iron(III) 5,10,15,20-Tetracyclohexylporphyrin

Hyperfine couplings and ¹³C relaxation in alkylamines coordinated to Ni(II) acetylacetonate

Substituent Effects on ¹³ C Chemical Shifts in Aliphatic Molecular Systems. Dependence on Constitution and Stereochemistry

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Studies on the proton and carbon-13 contact shifts for .sigma.-bonded molecules. Stereospecific electron spin transmission in cyclic and bicyclic amines

Cited by 18 publications

References 5 publications

Stabilization of the Less Common (dxzdyz)4(dxy)1Iron(III) Porphyrin Ground Electronic State: 1H NMR Investigations of Iron(III) 5,10,15,20-Tetracyclohexylporphyrin

Stabilization of the Less Common (dxzdyz)4(dxy)1Iron(III) Porphyrin Ground Electronic State: 1H NMR Investigations of Iron(III) 5,10,15,20-Tetracyclohexylporphyrin

Hyperfine couplings and 13C relaxation in alkylamines coordinated to Ni(II) acetylacetonate

Substituent Effects on 13 C Chemical Shifts in Aliphatic Molecular Systems. Dependence on Constitution and Stereochemistry

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Stabilization of the Less Common (d_xzd_y_z)⁴(d_x_y)¹Iron(III) Porphyrin Ground Electronic State: ¹H NMR Investigations of Iron(III) 5,10,15,20-Tetracyclohexylporphyrin

Stabilization of the Less Common (d_xzd_y_z)⁴(d_x_y)¹Iron(III) Porphyrin Ground Electronic State: ¹H NMR Investigations of Iron(III) 5,10,15,20-Tetracyclohexylporphyrin

Hyperfine couplings and ¹³C relaxation in alkylamines coordinated to Ni(II) acetylacetonate

Substituent Effects on ¹³ C Chemical Shifts in Aliphatic Molecular Systems. Dependence on Constitution and Stereochemistry