|Budget Amount *help
¥3,000,000 (Direct Cost : ¥3,000,000)
Fiscal Year 2000 : ¥700,000 (Direct Cost : ¥700,000)
Fiscal Year 1999 : ¥700,000 (Direct Cost : ¥700,000)
Fiscal Year 1998 : ¥1,600,000 (Direct Cost : ¥1,600,000)
The electron configuration of low spin iron (III) porphyrin complexes is generally represented as (d_<xy>)^2(d_<xz>, d_<yz>)^3(d_π type). Recently, We have found that the energy levels of the iron d_<xy> and d_π(d_<xz>, d_<yz>) orbitals are reversed in some complexes with highly nonplanar porphyrin rings, resulting in the formation of the less common (d_<xz>, d_<yz>)^4(d_<xy>)^1(d_<xy> type) ground state. We started the project three years ago to reveal the factors that affect the electronic ground state of low spin iron (III), manganese (III), and chromium (III) porphyrin complexes.
Three factors that could affect the electron configuration of low spin iron (III) are, i) coordination ability of axial ligands, ii) deformation mode of porphyrin ring, and iii) electronic effect of the peripheral substituents. By the extensive studies using ^1H NMR, ^<13>C NMR, and EPR spectra, we have found that i) strong axial ligands such as imidazole and dimethylaminopyridine stabilize the d_π type, while weak axial ligands such as tert-butylisocyanide and 4-cyanopiridine stabilize the d_<xy> type, ii) highly saddle shaped porphyrin rings such as octaethyltetraphenyl-porphyrin stabilize the d_π type, while highly ruffled porphyrin rings such as meso-tetraisopropylporphyrin stabilize the d_<xy> type, iii) porphyrins carrying electron withdrawing substituents at the meso positions stabilize the d_π type, while those with electron donating groups prefer the d_<xy> type.
We have then examined the effect of porphyrin deformation on the electron configuration of manganese (III) porphyrin complexes. However, even by the addition of excess cyanide, the expected bis-adduct was not a sole product. Instead, the mixture of the mono and bis-addcut was observed. Close examination of the coordination reaction has revealed that the ratio, mono vs. bis, chages depending upon the nature of the solvents used. The study to reveal this interesting phenomenon is now in progress.