Mikio Nakamura - Academia.edu (original) (raw)
Papers by Mikio Nakamura
Inorganic Chemistry, 2007
Substituent effects of the meso-aryl (Ar) groups on the 1H and 13C NMR chemical shifts in a serie... more Substituent effects of the meso-aryl (Ar) groups on the 1H and 13C NMR chemical shifts in a series of low-spin highly saddled iron(III) octaethyltetraarylporphyrinates, [Fe(OETArP)L2]+, where axial ligands (L) are imidazole (HIm) and tert-butylisocyanide ((t)BuNC), have been examined to reveal the nature of the interactions between metal and porphyrin orbitals. As for the bis(HIm) complexes, the crystal and molecular structures have been determined by X-ray crystallography. These complexes have shown a nearly pure saddled structure in the crystal, which is further confirmed by the normal-coordinate structural decomposition method. The substituent effects on the CH2 proton as well as meso and CH2 carbon shifts are fairly small in the bis(HIm) complexes. Since these complexes adopt the (d(xy))2(d(xz), d(yz))3 ground state as revealed by the electron paramagnetic resonance (EPR) spectra, the unpaired electron in one of the metal dpi orbitals is delocalized to the porphyrin ring by the interactions with the porphyrin 3e(g)-like orbitals. A fairly small substituent effect is understandable because the 3e(g)-like orbitals have zero coefficients at the meso-carbon atoms. In contrast, a sizable substituent effect is observed when the axial HIm is replaced by (t)BuNC. The Hammett plots exhibit a large negative slope, -220 ppm, for the meso-carbon signals as compared with the corresponding value, +5.4 ppm, in the bis(HIm) complexes. Since the bis((t)BuNC) complexes adopt the (d(xz), d(yz))4(d(xy))1 ground state as revealed by the EPR spectra, the result strongly indicates that the half-filled dxy orbital interacts with the specific porphyrin orbitals that have large coefficients on the meso-carbon atoms. Thus, we have concluded that the major metal-porphyrin orbital interaction in low-spin saddle-shaped complexes with the (d(xz), d(yz))4(d(xy))1 ground state should take place between the d(xy) and a(2u)-like orbital rather than between the dxy and a(1u)-like orbital, though the latter interaction is symmetry-allowed in saddled D(2d) complexes. Fairly weak spin delocalization to the meso-carbon atoms in the complexes with electron-withdrawing groups is then ascribed to the decrease in spin population in the d(xy) orbital due to a smaller energy gap between the d(xy) and dpi orbitals. In fact, the energy levels of the d(xy) and dpi orbitals are completely reversed in the complex carrying a strongly electron-withdrawing substituent, the 3,5-bis(trifluoromethyl)phenyl group, which results in the formation of the low-spin complex with an unprecedented (d(xy))2(d(xz), d(yz))3 ground state despite the coordination of (t)BuNC.
Acta Crystallographica Section E Structure Reports Online, 2011
metal-organic compounds m1904 Ohgo et al. [Fe(C 36 H 36 N 4 O 4)Cl] Acta Cryst. (2011). E67, m190... more metal-organic compounds m1904 Ohgo et al. [Fe(C 36 H 36 N 4 O 4)Cl] Acta Cryst. (2011). E67, m1903-m1904 supporting information sup-1
Chemical Communications, 2006
Inorganic Chemistry, 2006
Chemical Communications, 2006
Acta Crystallographica Section A Foundations of Crystallography
Microsymposia of [Ni(tmdt)2] and [Au(tmdt)2]. It was quite surprising that in spite of the compre... more Microsymposia of [Ni(tmdt)2] and [Au(tmdt)2]. It was quite surprising that in spite of the compressed crystalline powder sample, the room temperature conductivity of [Pt(tmdt)2] was as high as 350 S cm-1 and temperature dependence of the resistivity was metallic down to 4 K. Here, our recent studies on crystal structures and their physical properties of single-component molecular conductors with different central metal atoms (Cu, Zn, Co) will also be presented.
Journal of inorganic biochemistry, 2018
Pyrrocorphin is an air-sensitive porphyrinoid with a highly reduced hexahydroporphyrin core. In c... more Pyrrocorphin is an air-sensitive porphyrinoid with a highly reduced hexahydroporphyrin core. In contrast, pyrrolidine-fused pyrrocorphin (Pyr) obtained by successive 1,3-dipolar cycloaddition reactions of azomethine ylide to 5,10,15,20-tetrakis(pentafluorophenyl)porphyrin is less air-sensitive. In order to reveal the effect of highly reduced porphyrin rings on the physicochemical properties of their metal complexes, we have prepared diamagnetic (S=0) Ni(II) complex Ni(II)(Pyr). The addition of excess pyridine (Py) to the toluene solution of Ni(II)(Pyr) yielded five-coordinate Ni(II)(Pyr)(Py), which was then completely converted to six-coordinate paramagnetic (S=1) Ni(II)(Pyr)(Py). The latter was characterized by UV-Vis, H NMR, CV, SQUID, and X-ray crystallography as well as DFT calculations. As compared with analogous complexes of porphyrin (Por), chlorin (Chl), and isobacteriochlorin (Iso) reported by Herges and co-workers (R. Herges et al., Inorg. Chem. 2015), Ni(II)(Pyr)(Py) has ...
Acta Crystallographica Section C Crystal Structure Communications
ABSTRACT The title complex, [Fe(C32H36N4)(C4H8O)2]ClO4, shows an S4-ruffled porphyrin ring, where... more ABSTRACT The title complex, [Fe(C32H36N4)(C4H8O)2]ClO4, shows an S4-ruffled porphyrin ring, where the maximum deviation of the meso-carbon from the least-squares plane of the [Fe(C20N4)] core is as high as 0.675 (9) Å. This is the highest class of deviation among S4-ruffled iron(III) porphyrin complexes. The average Fe—Np bond distance is 1.967 (12) Å (Np denotes an N atom of the equatorial ligand).
Coordination Chemistry Reviews
ABSTRACT This review describes the effects of highly deformed porphyrin ring on the electronic st... more ABSTRACT This review describes the effects of highly deformed porphyrin ring on the electronic structures of iron(III) porphyrinates, which includes (i) the electron configurations in low-spin (S = 1/2) ruffled complexes, (ii) the contribution of the intermediate-spin (S = 3/2) state in the spin-admixed (S = 5/2, 3/2) complexes with ruffled and saddled porphyrin ring, and (iii) the novel spin crossover (S = 1/2, S = 3/2) phenomenon in saddled complexes, with a special emphasis on the use of 1H NMR, 13C NMR, and EPR spectroscopy.
Inorganic Chemistry, 2016
Dalton transactions (Cambridge, England : 2003), Jan 20, 2016
In contrast to the general tendency that six coordinate iron(iii) porphyrin complexes with neutra... more In contrast to the general tendency that six coordinate iron(iii) porphyrin complexes with neutral oxygen ligands adopt a high-spin state in a wide range of temperature, some complexes with substituted pyridine N-oxides have exhibited spin-crossover from high-spin to low-spin states with decreasing temperature both in solution and in the solid state.
Tetrahedron Letters, 1973
Inorganic Chemistry, Oct 1, 2003
The electronic states of a series of saddle-shaped porphyrin complexes [Fe(OMTPP)L 2 ] + and [Fe(... more The electronic states of a series of saddle-shaped porphyrin complexes [Fe(OMTPP)L 2 ] + and [Fe(TBTXP)L 2 ] + have been examined in solution by 1 H NMR, 13 C NMR, and EPR spectroscopy and by magnetic measurements. While [Fe(OMTPP)(DMAP) 2 ] + and [Fe(TBTXP)(DMAP) 2 ] + maintain the low-spin (S) 1 / 2) state, [Fe(OMTPP)(THF) 2 ] + and [Fe(TBTXP)(THF) 2 ] + exhibit an essentially pure intermediate-spin (S) 3 / 2) state over a wide range of temperatures. In contrast, the Py and 4-CNPy complexes of OMTPP and TBTXP exhibit a spin transition from S) 3 / 2 to S) 1 / 2 as the temperature was decreased from 300 to 200 K. Thus, the magnetic behavior of these complexes is similar to that of [Fe(OETPP)Py 2 ] + reported in our previous paper (Ikeue, T.; Ohgo, Y.; Yamaguchi, T.; Takahashi, M.; Takeda, M.; Nakamura, M. Angew. Chem., Int. Ed. 2001, 40, 2617−2620) in the context that all these complexes exhibit a novel spin crossover phenomenon in solution. Close examination of the NMR and EPR data of [Fe(OMTPP)L 2 ] + and [Fe(TBTXP)L 2 ] + (L) Py, 4-CNPy) revealed, however, that these complexes adopt the less common (d xz , d yz) 4 (d xy) 1 electron configuration at low temperature in contrast to [Fe(OETPP)Py 2 ] + which shows the common (d xy) 2 (d xz , d yz) 3 electron configuration. These observations have been attributed to the flexible nature of the OMTPP and TBTXP cores as compared with that of OETPP; the relatively flexible OMTPP and TBTXP cores can ruffle the porphyrin ring and adopt the (d xz , d yz) 4 (d xy) 1 electron configuration at low temperature. Therefore, this study reveals that the rigidity of porphyrin cores is an important factor in determining the spin crossover pathways.
Chemistry Letters, Aug 1, 1995
ABSTRACT
J Porphyr Phthalocya, 2008
Electronic structure of a series of five-coordinate Fe ( OArTAzP ) X ( OAr = octaaryltetraazaporp... more Electronic structure of a series of five-coordinate Fe ( OArTAzP ) X ( OAr = octaaryltetraazaporphyrin , X = Cl -, Br -, I -; Ar = 4-tert-butylphenyl) have been examined on the basis of 1 H NMR, 13 C NMR, and EPR spectroscopy as well as SQUID magnetometry. These complexes adopt the intermediate-spin state as in the case of analogous complexes reported by Fitzgerald et al. (Inorg. Chem. 1992; 31: 2006-2013) and Stuzhin et al. (Inorg. Chim. Acta 1995; 236: 131-139). The 13 C NMR studies using 13 C -enriched complexes at the pyrrole α positions have revealed that the pyrrole- C α signals appear at extraordinary upfield positions, i.e. -130 to -250 ppm at 273 K, due to the d z2-a2 u and d π-3 e g interactions. The Curie plots of the pyrrole- C α signals have further revealed that the iodide complex adopts a much purer intermediate-spin state than the bromide and chloride complexes. In contrast to the case of Fe ( OArTAzP ) X , six-coordinate [ Fe ( OArTAzP )( CN )2]- showed the pyrrole- C α signal at 47 ppm at 273 K, which indicates that the complex adopts the low-spin state with the ( d xy)2( d xz, d yz)3 electron configuration. Thus, the 13 C NMR chemical shift of the pyrrole- C α signal turns out to be quite a good probe to elucidate the spin state and electron configuration of iron(III) tetraazaporphyrins, where the 1H NMR spectroscopy is less useful because of the absence of the hydrogen atoms as well as the alkyl or aryl groups directly attached to the meso positions.
Journal of the American Chemical Society, 2003
On the basis of the difference in meso-13C chemical shifts, we have concluded that the intermedia... more On the basis of the difference in meso-13C chemical shifts, we have concluded that the intermediate-spin iron(III) complexes with highly ruffled and highly saddled porphyrins have different electron configurations. While the latter has a conventional (dxy)2(dxz, dyz)2(dz2)1, the former adopts a novel (dxz, dyz)3(dxy)1(dz2)1.
Inorganic Chemistry, 2007
Substituent effects of the meso-aryl (Ar) groups on the 1H and 13C NMR chemical shifts in a serie... more Substituent effects of the meso-aryl (Ar) groups on the 1H and 13C NMR chemical shifts in a series of low-spin highly saddled iron(III) octaethyltetraarylporphyrinates, [Fe(OETArP)L2]+, where axial ligands (L) are imidazole (HIm) and tert-butylisocyanide ((t)BuNC), have been examined to reveal the nature of the interactions between metal and porphyrin orbitals. As for the bis(HIm) complexes, the crystal and molecular structures have been determined by X-ray crystallography. These complexes have shown a nearly pure saddled structure in the crystal, which is further confirmed by the normal-coordinate structural decomposition method. The substituent effects on the CH2 proton as well as meso and CH2 carbon shifts are fairly small in the bis(HIm) complexes. Since these complexes adopt the (d(xy))2(d(xz), d(yz))3 ground state as revealed by the electron paramagnetic resonance (EPR) spectra, the unpaired electron in one of the metal dpi orbitals is delocalized to the porphyrin ring by the interactions with the porphyrin 3e(g)-like orbitals. A fairly small substituent effect is understandable because the 3e(g)-like orbitals have zero coefficients at the meso-carbon atoms. In contrast, a sizable substituent effect is observed when the axial HIm is replaced by (t)BuNC. The Hammett plots exhibit a large negative slope, -220 ppm, for the meso-carbon signals as compared with the corresponding value, +5.4 ppm, in the bis(HIm) complexes. Since the bis((t)BuNC) complexes adopt the (d(xz), d(yz))4(d(xy))1 ground state as revealed by the EPR spectra, the result strongly indicates that the half-filled dxy orbital interacts with the specific porphyrin orbitals that have large coefficients on the meso-carbon atoms. Thus, we have concluded that the major metal-porphyrin orbital interaction in low-spin saddle-shaped complexes with the (d(xz), d(yz))4(d(xy))1 ground state should take place between the d(xy) and a(2u)-like orbital rather than between the dxy and a(1u)-like orbital, though the latter interaction is symmetry-allowed in saddled D(2d) complexes. Fairly weak spin delocalization to the meso-carbon atoms in the complexes with electron-withdrawing groups is then ascribed to the decrease in spin population in the d(xy) orbital due to a smaller energy gap between the d(xy) and dpi orbitals. In fact, the energy levels of the d(xy) and dpi orbitals are completely reversed in the complex carrying a strongly electron-withdrawing substituent, the 3,5-bis(trifluoromethyl)phenyl group, which results in the formation of the low-spin complex with an unprecedented (d(xy))2(d(xz), d(yz))3 ground state despite the coordination of (t)BuNC.
Acta Crystallographica Section E Structure Reports Online, 2011
metal-organic compounds m1904 Ohgo et al. [Fe(C 36 H 36 N 4 O 4)Cl] Acta Cryst. (2011). E67, m190... more metal-organic compounds m1904 Ohgo et al. [Fe(C 36 H 36 N 4 O 4)Cl] Acta Cryst. (2011). E67, m1903-m1904 supporting information sup-1
Chemical Communications, 2006
Inorganic Chemistry, 2006
Chemical Communications, 2006
Acta Crystallographica Section A Foundations of Crystallography
Microsymposia of [Ni(tmdt)2] and [Au(tmdt)2]. It was quite surprising that in spite of the compre... more Microsymposia of [Ni(tmdt)2] and [Au(tmdt)2]. It was quite surprising that in spite of the compressed crystalline powder sample, the room temperature conductivity of [Pt(tmdt)2] was as high as 350 S cm-1 and temperature dependence of the resistivity was metallic down to 4 K. Here, our recent studies on crystal structures and their physical properties of single-component molecular conductors with different central metal atoms (Cu, Zn, Co) will also be presented.
Journal of inorganic biochemistry, 2018
Pyrrocorphin is an air-sensitive porphyrinoid with a highly reduced hexahydroporphyrin core. In c... more Pyrrocorphin is an air-sensitive porphyrinoid with a highly reduced hexahydroporphyrin core. In contrast, pyrrolidine-fused pyrrocorphin (Pyr) obtained by successive 1,3-dipolar cycloaddition reactions of azomethine ylide to 5,10,15,20-tetrakis(pentafluorophenyl)porphyrin is less air-sensitive. In order to reveal the effect of highly reduced porphyrin rings on the physicochemical properties of their metal complexes, we have prepared diamagnetic (S=0) Ni(II) complex Ni(II)(Pyr). The addition of excess pyridine (Py) to the toluene solution of Ni(II)(Pyr) yielded five-coordinate Ni(II)(Pyr)(Py), which was then completely converted to six-coordinate paramagnetic (S=1) Ni(II)(Pyr)(Py). The latter was characterized by UV-Vis, H NMR, CV, SQUID, and X-ray crystallography as well as DFT calculations. As compared with analogous complexes of porphyrin (Por), chlorin (Chl), and isobacteriochlorin (Iso) reported by Herges and co-workers (R. Herges et al., Inorg. Chem. 2015), Ni(II)(Pyr)(Py) has ...
Acta Crystallographica Section C Crystal Structure Communications
ABSTRACT The title complex, [Fe(C32H36N4)(C4H8O)2]ClO4, shows an S4-ruffled porphyrin ring, where... more ABSTRACT The title complex, [Fe(C32H36N4)(C4H8O)2]ClO4, shows an S4-ruffled porphyrin ring, where the maximum deviation of the meso-carbon from the least-squares plane of the [Fe(C20N4)] core is as high as 0.675 (9) Å. This is the highest class of deviation among S4-ruffled iron(III) porphyrin complexes. The average Fe—Np bond distance is 1.967 (12) Å (Np denotes an N atom of the equatorial ligand).
Coordination Chemistry Reviews
ABSTRACT This review describes the effects of highly deformed porphyrin ring on the electronic st... more ABSTRACT This review describes the effects of highly deformed porphyrin ring on the electronic structures of iron(III) porphyrinates, which includes (i) the electron configurations in low-spin (S = 1/2) ruffled complexes, (ii) the contribution of the intermediate-spin (S = 3/2) state in the spin-admixed (S = 5/2, 3/2) complexes with ruffled and saddled porphyrin ring, and (iii) the novel spin crossover (S = 1/2, S = 3/2) phenomenon in saddled complexes, with a special emphasis on the use of 1H NMR, 13C NMR, and EPR spectroscopy.
Inorganic Chemistry, 2016
Dalton transactions (Cambridge, England : 2003), Jan 20, 2016
In contrast to the general tendency that six coordinate iron(iii) porphyrin complexes with neutra... more In contrast to the general tendency that six coordinate iron(iii) porphyrin complexes with neutral oxygen ligands adopt a high-spin state in a wide range of temperature, some complexes with substituted pyridine N-oxides have exhibited spin-crossover from high-spin to low-spin states with decreasing temperature both in solution and in the solid state.
Tetrahedron Letters, 1973
Inorganic Chemistry, Oct 1, 2003
The electronic states of a series of saddle-shaped porphyrin complexes [Fe(OMTPP)L 2 ] + and [Fe(... more The electronic states of a series of saddle-shaped porphyrin complexes [Fe(OMTPP)L 2 ] + and [Fe(TBTXP)L 2 ] + have been examined in solution by 1 H NMR, 13 C NMR, and EPR spectroscopy and by magnetic measurements. While [Fe(OMTPP)(DMAP) 2 ] + and [Fe(TBTXP)(DMAP) 2 ] + maintain the low-spin (S) 1 / 2) state, [Fe(OMTPP)(THF) 2 ] + and [Fe(TBTXP)(THF) 2 ] + exhibit an essentially pure intermediate-spin (S) 3 / 2) state over a wide range of temperatures. In contrast, the Py and 4-CNPy complexes of OMTPP and TBTXP exhibit a spin transition from S) 3 / 2 to S) 1 / 2 as the temperature was decreased from 300 to 200 K. Thus, the magnetic behavior of these complexes is similar to that of [Fe(OETPP)Py 2 ] + reported in our previous paper (Ikeue, T.; Ohgo, Y.; Yamaguchi, T.; Takahashi, M.; Takeda, M.; Nakamura, M. Angew. Chem., Int. Ed. 2001, 40, 2617−2620) in the context that all these complexes exhibit a novel spin crossover phenomenon in solution. Close examination of the NMR and EPR data of [Fe(OMTPP)L 2 ] + and [Fe(TBTXP)L 2 ] + (L) Py, 4-CNPy) revealed, however, that these complexes adopt the less common (d xz , d yz) 4 (d xy) 1 electron configuration at low temperature in contrast to [Fe(OETPP)Py 2 ] + which shows the common (d xy) 2 (d xz , d yz) 3 electron configuration. These observations have been attributed to the flexible nature of the OMTPP and TBTXP cores as compared with that of OETPP; the relatively flexible OMTPP and TBTXP cores can ruffle the porphyrin ring and adopt the (d xz , d yz) 4 (d xy) 1 electron configuration at low temperature. Therefore, this study reveals that the rigidity of porphyrin cores is an important factor in determining the spin crossover pathways.
Chemistry Letters, Aug 1, 1995
ABSTRACT
J Porphyr Phthalocya, 2008
Electronic structure of a series of five-coordinate Fe ( OArTAzP ) X ( OAr = octaaryltetraazaporp... more Electronic structure of a series of five-coordinate Fe ( OArTAzP ) X ( OAr = octaaryltetraazaporphyrin , X = Cl -, Br -, I -; Ar = 4-tert-butylphenyl) have been examined on the basis of 1 H NMR, 13 C NMR, and EPR spectroscopy as well as SQUID magnetometry. These complexes adopt the intermediate-spin state as in the case of analogous complexes reported by Fitzgerald et al. (Inorg. Chem. 1992; 31: 2006-2013) and Stuzhin et al. (Inorg. Chim. Acta 1995; 236: 131-139). The 13 C NMR studies using 13 C -enriched complexes at the pyrrole α positions have revealed that the pyrrole- C α signals appear at extraordinary upfield positions, i.e. -130 to -250 ppm at 273 K, due to the d z2-a2 u and d π-3 e g interactions. The Curie plots of the pyrrole- C α signals have further revealed that the iodide complex adopts a much purer intermediate-spin state than the bromide and chloride complexes. In contrast to the case of Fe ( OArTAzP ) X , six-coordinate [ Fe ( OArTAzP )( CN )2]- showed the pyrrole- C α signal at 47 ppm at 273 K, which indicates that the complex adopts the low-spin state with the ( d xy)2( d xz, d yz)3 electron configuration. Thus, the 13 C NMR chemical shift of the pyrrole- C α signal turns out to be quite a good probe to elucidate the spin state and electron configuration of iron(III) tetraazaporphyrins, where the 1H NMR spectroscopy is less useful because of the absence of the hydrogen atoms as well as the alkyl or aryl groups directly attached to the meso positions.
Journal of the American Chemical Society, 2003
On the basis of the difference in meso-13C chemical shifts, we have concluded that the intermedia... more On the basis of the difference in meso-13C chemical shifts, we have concluded that the intermediate-spin iron(III) complexes with highly ruffled and highly saddled porphyrins have different electron configurations. While the latter has a conventional (dxy)2(dxz, dyz)2(dz2)1, the former adopts a novel (dxz, dyz)3(dxy)1(dz2)1.