Takahisa Ikeue

Saddle-Shaped Six-Coordinate Iron(III) Porphyrin Complexes Showing a Novel Spin Crossover between S=1/2 and S=3/2 Spin States

The field strength of the axial ligands determines the spin state of saddled iron(III) porphyrin complexes. Strong axial ligands (L), such as imidazole and 4-dimethylaminopyridine, lead to the formation of complexes with a pure S=1/2 state, while weak ligands, such as THF, give complexes with a pure S=3/2 state. Intermediate strength ligands, such as pyridine and 4-cyanopyridine, give complexes that show a novel spin crossover between the S=1/2 and S=3/2 states.

Electronic effects of para-substituents on the electron configuration of dicyano[meso-tetrakis(p-substituted phenyl)porphyrinato]iron(III) complexes

Abstract There are two types of electron configuration, (dxy)2(dxz, dyz)3 and (dxz, dyz)4(dxy)1, in low spin iron(III) porphyrin complexes. In order to reveal how the electronic effect of substituents affects the electron configuration of low spin iron(III) porphyrin complexes, we have examined the 13C NMR, 1H NMR, and EPR spectra of a series of tetrabutylammonium (dicyano)[meso-tetrakis(p-substituted phenyl)porphyrinato]ferrate(III), [Fe(p-X–TPP)(CN)2]−Bu4N+, in both CD2Cl2 and CD3OD solutions. The chemical shifts of the meso carbon signals, which sharply reflect the electron configuration of low spin iron(III), have changed to a great extent depending on the electron-donating or electron-withdrawing ability of the para-substituent. The isotropic shifts of the meso-carbon signals of [Fe(p-X–TPP)(CN)2]−Bu4N+ are determined on the basis of the meso-carbon chemical shifts of the corresponding diamagnetic cobalt(III) complexes, [Co(p-X–TPP)(CN)2]−Bu4N+. The plots of the isotropic shifts against Hammett σp values have yielded good linear lines with the slopes, −22 and −69 ppm, in CD2Cl2 and CD3OD, respectively. On the basis of these results, we have concluded that the electron-withdrawing groups at the phenyl para-positions stabilize the (dxy)2(dxz, dyz)3 state while the electron-donating groups at the same positions stabilize the (dxz, dyz)4(dxy)1 state. The conclusion is further supported by the 1H NMR and EPR results.

Chloro­(3,6,13,16-tetraethyl-2,7,12,17-tetra­methyl­porphycenato-κ4N)iron(III) chloro­form solvate

The X-ray crystallographic analysis of the title complex, chloro[3,10,13,20-tetraethyl-4,9,14,19-tetramethylpentacyclo[16.2.1.1(2,5).1(8,11).1(12,15)]tetracosa-2,4,6,8(23),9,12,14,16,18(21),19-decaene]iron(III) chloroform solvate, [Fe(C(33)H(37)N(4))Cl].CHCl(3), reveals a twisted macrocyclic framework with a slightly distorted rectangular pyramidal core, where the deviation of the central Fe(III) atom from the least-squares plane of the C(20)N(4) core is 0.594 (1) A. Some important bond distances are as follows: Fe-N 2.019 (3), 2.026 (3), 2.028 (3) and 2.034 (3) A; Fe-Cl 2.232 (1) A.

Barriers to rotation of axially coordinated imidazole ligands in nonplanar meso-tetraalkylporphyrinato-cobalt(III) complexes

Dynamic NMR study of a series of meso-[Co(TRP)(L)2]Cl, where R is an alkyl group and L is a substituted imidazole, has been carried out. While the complexes with unhindered imidazole show no splitting of the signals, those with bulky imidazoles exhibit change in line shape, indicating the hindered imidazole rotation. The activation free energy increases as R and/or L become bulkier. Based on the red-shifted Soret and Q bands in the UV-Visible and the downfield shifted imidazole protons in the 1H NMR spectra of these complexes as compared with the meso unsubstituted complexes, it is concluded that the deformation of the porphyrin ring slows down the rate of rotation of the coordinated ligand.

Effects of a nonplanar porphyrin rings on the spin–spin interactions in low-spin ferric porphyrin radical cations

Low-spin ferric porphyrin radical cations formed by the oxidation of chloro(meso-tetraalkylporphyrinato)iron(III) followed by the addition of bulky 2-methylimidazole show antiferromagnetic coupling, which is interpreted in terms of the interaction between porphyrin a2u and iron d(xy), orbitals caused by the S4 ruffling of the porphyrin core.

Highly saddle shaped (porphyrinato)iron(III) iodide with a pure intermediate spin state

Combined analyses using NMR, EPR and Mössbauer spectroscopy as well as SQUID magnetometry have revealed that highly saddle shaped Fe(OETPP)I adopts an essentially pure intermediate spin state in spite of the coordination of an iodide ligand.

Formation of pure intermediate spin complexes in highly nonplanar iron(III) porphyrins

Bis(thf)(porphyrinato)iron(III) complexes with nhighly S4-ruffled and S4-saddled nporphyrin cores are determined to be very pure intermediate spin complexes non the basis of NMR, EPR, Mossbauer, and magnetic data.

Chloro(meso-tetrapropylporphyrinato)iron(III)

In the chloroiron(III) complex of meso-tetrapropylporphyrin, [Fe(C 32 H 36 N 4 )Cl], the Fe III atom has slightly distorted square-pyramidal coordination. The porphyrin ring shows a typical S 4 -ruffled structure in addition to a normally observed domed core; the deviations of the meso-C and Fe atoms from the least-squares plane of the C 20 N 4 core are 0.366(4) (maximum) and 0.578 (1) A, respectively. The average Fe-N p bond distance is 2.063 (4) A.

SYNTHESIS AND PROPERTIES OF C-AZA-2-DEOXY-L-LYXONUCLEOSIDES

‘C-Aza-2-deoxy-L-lyxonucleosides’ in which a sugar ring oxygen is replaced with a nitrogen atom are synthesized from 2-deoxy-3,5-O-(tetraisopropyldisiloxane-1,3-diyl)-D-erythro-pentofuranose via a sequential procedure of the addition of lithium salts of aromatic heterocycles, Swern oxidation and reductive aminocyclization. Their structures are determined mainly by X-ray crystallography and NMR measurements. Their bioassay is also described.