Kozo Fukui

Curve-Structured Phenalenyl Chemistry : Synthesis, Electronic Structure, and Bowl-Inversion Barrier of a Phenalenyl-Fused Corannulene Anion

We have demonstrated the features of curve-structured phenalenyl chemistry, for the first time. A phenalenyl-fused corannulene anion has been designed by the annelation of a six-memberd ring across peri-positions of corannulene and generated as a stable species in a degassed solution. The 1H and 13C NMR spectra have shown the highly symmetrical structure and high-field shifts of protons and carbons at the asterisked positions in the chemical structure, indicating the occurrence of large negative charge densities at these positions. These results well agree with the HOMO picture and the electrostatic potential surface, demonstrating the phenalenyl anion-type electronic structure is retained in the curved-surface pi-system. The calculated bowl-inversion barrier of the anion (11.3 kcal/mol) is larger than that of corannulene (9.2 kcal/mol) because of peri-annelation of the corannulene skeleton. The calculations of the barriers of the neutral radical (12.6 kcal/mol), radical dianion (8.1 kcal/mol), and trianion (5.4 kcal/mol) of the phenalenyl-fused corannulene have exhibited a stepwise flattening of the curvature with increase in negative charge. Therefore, we have revealed that the bowl-inversion barrier of the anion is governed by the setoff of the peri-annelation and negative charge effects.

Electronic structure of a stable phenalenyl radical in crystalline state as studied by SQUID measurements, cw-ESR, and 13C CP/MAS NMR spectroscopy

Abstract A neat single crystal of phenalenyl radical was obtained for the first time by introducing the substituent group of tert -butyl X-ray structure analysis of the crystal of 2,5,8-tri- tert -butylphenalenyl( 2 ) showed that the two planar radicals face each other with inversion symmetry and are dimerized in the monoclinic crystal. This is supported by the magnetic susceptibility(χ) measurement of the crystalline solid state of 2 The observed temperature dependence of χT was reproduced by assuming the thermal equilibrium between a singlet ground state and excited triplet state of the dimer (2 J/k B = −2000K) with traces of paramagnetic impurity molecules (0.3mol%). The electronic structure of the radical dimer in the crystalline state has been identified also by single-crystal ESR and 13 C CP/MAS NMR measurements. The origin of the large antiferromagnetic interaction is discussed in terms of both the experimentally determined π-spin density distribution of monomer radicals and π MO calculations.

6-Oxophenalenoxyl derivatives covalently linked to TTF moieties: synthesis, ESR/ENDOR measurements, and DFT calculations

Abstract The efficient synthesis, characterization, and electronic properties of new 6-oxophenalenoxyls covalently linked to TTF moieties are described in terms of Stille-coupling reactions, ESR/ 1 H-ENDOR techniques, and DFT calculations.

A synthetic study of metal complexes of coordinated neutral radicals based on an azaphenalenyl system

Abstract A new neutral radical ligand, 5,8-di-tert-butyl-2-(4′,6′-dimethylpyrimidine-2′-yl)-1,3-diazaphenalenyl (2), has been designed on the basis of 1,3-diazaphenalenyl system. As a study for the metal complexes of coordinated neutral radical 6, we have synthesized the metal complex coordinated diazaphenalene 3 by a combination of CoCl2 with 1,3-diazaphenalene 4. The 1,3-diazaphenalene of the metal complex 3 in the crystal was planar and nearly coplanar with the pyrimidine ring, giving the first study on the structurally characterized metal complex based on the azaphenalene system. Preliminary magnetic susceptibility measurements have revealed that 3 is a spin-quartet in the ground state.

Electronic-spin and columnar crystal structures of stable 2,5,8-tri-tert-butyl-1,3-diazaphenalenyl radical

Abstract 1,3-Diazaphenalenyl is a typical example of the isoelectronic mode of heteroatomic modification for phenalenyl. Recently, we have designed and isolated 2,5,8-tri-tert-butyl-1,3-diazaphenalenyl (6) as the first example of stable azaphenalenyl. For further elucidation of the electronic and solid-state structures of 6, 15N atoms incorporated 1,3-diazaphenalenyl 7 was designed. New nitration reaction by K15NO3 of 2,7-di-tert-butylnaphthalene has enabled us to accomplish effective introduction of 15N atoms and synthesis of 7. The spin structure of 1,3-(15N2)diazaphenalenyl 7 was unequivocally determined by the ratio of the hfcc for 14N and 15N (A14N/A15N=0.292/0.409=0.714), which was equal to the ratio of each gyromagnetic ratio (γ14N/γ15N=0.713). Under an air atmosphere, the radical 7 decomposes slowly, but most of it remains unchanged for weeks. By comparing the spin densities of 7 with those of parent phenalenyl radical 2, it appears that the spin densities of the 1- and 3-positions decrease appreciably, while those of the 4-, 6-, 7-, and 9-positions increase. The radical 7 forms the syn-dimer with gable structure in the crystal, and the dimer stacks in a columnar structure motif.

Electronic Structure of a Stable Phenalenyl Radical as Studied by ESR/ENDOR, Paramagnetic NMR Spectroscopy and SQUID Measurements

Abstract We have studied magnetic properties and electronic structures of a novel persistent neutral radical, 2,5,8-tri-tert-butylphenalenyl(2), which is the first example of alternant hydrocarbon π-radical isolated in the crystalline state. The observed magnetic susceptibilities of polycrystalline sample 2 were reproduced by assuming the thermal equilibrium between singlet ground state and excited triplet state of the dimer (2J/k B = −2×103 K) with traces of paramagnetic impurity molecules (0.3mol%). The π-spin density distribution of radical 2 was determined by liquid-phase cw-ESR, 1H-ENDOR/TRIPLE, and paramagnetic 1H-NMR measurements. The origin of the large inter-molecular antiferromagnetic interaction in the crystal 2 was explained by an occurrence of effective SOMO-SOMO overlap between the two radicals on the six equivalent α-positions with large positive spin densities of the carbon sites.

Hexaazaphenalene derivatives: one-pot synthesis, hydrogen-bonded chiral helix, and fluorescence properties.

Symmetric hexaazaphenalenes (R = phenyl and tert-butyl) have been synthesized by one-pot condensations of corresponding amidine hydrochlorides with tricyanomethanide. The hexaazaphenalenes are linked with each other by a N-H···N hydrogen-bonding interaction in the crystalline states. Interestingly, a planar and achiral tert-butylated derivative was crystallized in a chiral space group with assembly of one-handed helical hydrogen-bonded chains. Hexaazaphenalenyl anions were isolated as air- and water-stable tetraethyl ammonium salts.

Synthesis and spin structure of 8-(p-halophenyl)-6-oxophenalenoxyl derivative

2,5-Di-tert-butyl-8-(p-iodophenyl)-6-oxophenalenoxyl has been synthesized as the first 6-oxophenalenoxyl derivative with halophenyl group, and its π-spin structure was unequivocally determined in terms of ESR/ENDOR/IRIPLE spectroscopies and the DFT calculation.

Redox-based spin diversity: a reversible topological spin switching in oxophenalenoxyl systems

A 6-oxophenalenoxyl system is found to be the first example of the molecular system with redox-based spin diversity nature. To generalize this nature, we focus on the 3-oxophenalenoxyl system as a topological isomer of 6-oxophenalenoxyl system. The radical dianion derivative 3 which is the redox state in the 3-oxophenalenoxyl system was successfully generated by the reduction of the corresponding hydroxyphenalenone 5 with potassium mirror. Our ESR/ENDOR/TRIPLE measurements and DFT calculation of 3 demonstrated that the 3-oxophenalenoxyl system has also redox-based spin diversity nature. In addition, for the elucidation of the interplay between spin and charge fluctuation in 3, we discuss a VB approach derived from MO calculations.

Generation and properties of 2,5,8-tri-tert-butyl-6-oxo-7,9-diazaphenalenoxyl

Novel neutral radical, 2,5,8-tri-tert-butyl-6-oxo-7,9-diazaphenalenoxyl, was designed on the basis of 6-oxophenalenoxyl and generated by the chemical oxidation of the corresponding tetraethylammonium salt. The spin density distribution was determined by ESR, ENDOR/TRIPLE measurements and the DFT calculations, showing that then-spin structure is similar to that of the 6-oxophenalenoxyl.