Naokazu Kano

Synthesis of the most intensely fluorescent azobenzene by utilizing the B-N interaction

A boron-substituted azobenzene, (E)-[2-(4-methoxyphenylazo)phenyl]bis(pentafluorophenyl)borane, presented the most intense fluorescence among the azobenzene derivatives.

Fluorescence Properties of Simple N-Substituted Aldimines with a B−N Interaction and Their Fluorescence Quenching by a Cyanide Ion

N-Aryl, N-alkyl, N-alkoxy, and N-amino derivatives of 2-[bis(pentafluorophenyl)boryl]benzylideneamine were synthesized by the condensation reactions of 2-[bis(pentafluorophenyl)boryl]benzaldehyde with the corresponding amines. Their structures were investigated by NMR and X-ray crystallographic analysis. Their properties were investigated by UV-vis and fluorescence spectroscopy. The boryl-substituted N-arylimines show blue or green fluorescence in hexane at room temperature, and their fluorescence efficiency is much higher than that of N-benzylideneaniline. In particular, the boryl-substituted N-(4-dimethylaminophenyl)imine showed strong green emissions with at least 7000 times higher fluorescence quantum yield (0.73) compared with that of N-benzylideneaniline. The boryl-substituted N-(1-indolyl)- and N-(9-carbazolyl)imines showed dual emissions, one of which was assignable as arising from the lowest singlet excited state and the other from the local excited state of the substituent on the imine nitrogen. The fluorescent properties of the boryl-substituted N-butyl- and N-methoxyimines were also investigated. Reactions of the N-arylimine derivatives with cyanide ion gave the corresponding cyanide adducts and quenched the fluorescence, indicating that these 2-[bis(pentafluorophenyl)boryl]benzylideneamine derivatives have a potential as a cyanide ion sensor.

Synthesis, structure, and thermolysis of pentacoordinate 1,3,2λ5-oxazaphosphetidines: the intermediates of aza-Wittig reactions

1,3,2λ5-Oxazaphosphetidines bearing the Martin ligand were synthesized by the reaction of the corresponding iminophosphorane and carbonyl compounds and characterized by X-ray crystallographic analysis. Thermolysis of the oxazaphosphetidine gave the cyclic phosphinate and the corresponding imine, indicating that the oxazaphosphetidine is an intermediate of the aza-Wittig reaction.

Synthesis, crystal structure, and photoreaction of a disiloxane bearing two 2-(phenylazo)phenyl groups

Abstract An E,E-1,1,3,3-tetrafluoro-1,3-bis[2-(phenylazo)phenyl]-1,3-disiloxane (E,E-2) was synthesized by hydrolysis of E-trifluoro[2-(phenylazo)phenyl]silane (E-1). Its structure was characterized by 1H-, 13C-, 19F-, and 29Si-NMR spectroscopy and X-ray crystallographic analysis showing two pentacoordinate silicon atoms with SiN interactions. Photoirradiation of E,E-2 caused both isomerization of the azo group and formation of the corresponding Z-1 in a short time, while upon standing in the dark the E-1 was formed very slowly.

Umpolung of a Hydrogen Atom of Water by Using a Hexacoordinated Phosphate and Its Application to Deuteride Reduction Reactions of Carbonyl Compounds

The polarity of a chemical bond is an important factor that determines the reactivity because a reaction of a positively charged atom with a negatively charged atom easily occurs. We report here a method for reversing the polarity of a hydrogen atom of water, which meant conversion of a protic hydrogen (H(delta+)) to a hydridic hydrogen (H(delta-)), by using a hexacoordinated phosphorus species. The method enables a reductive deuteration of carbonyl compounds utilizing inexpensive and easily usable D(2)O under mild conditions. The umpolung of a hydrogen atom was achieved by utilizing tautomerization of phosphorus compounds. Classical metal hydrides never have this function, and these results demonstrated the potential utility of nonmetallic compounds for umpolung of a hydrogen atom.

Synthesis, structure, and thermolysis of a novel spirotellurane bearing two 1,2-oxatelluretane rings, 1,5-dioxa-4λ4-telluraspiro[3.3]heptane: oxirane and olefin formation reactions

The first 1,5-dioxa-4λ 4 -telluraspiro[3.3]heptane was synthesized and its structure was determined by X-ray analysis. This tellurane gave the corresponding oxirane and olefin, as well as alcohol, upon heating, which were shown to be formed via a radical pathway.

Hypercoordination to a saturated carbon atom

Recently, the first heptacoordinate disilane [(MesCS 2 ) 2 MeSi] 2 1 was synthesized and shown to have a unique structure by X-ray analysis. Each of the silicon atoms is surrounded by three nonbonded thiobenzoylthio groups. We theoretically investigated the origins of the unusual geometry of 1 containing multiple hypercoordinations. The model compound [(HCS 2 ) 2 MeSi] 2 2a shows both the H-CSi-Si eclipsed conformation and the C-SiSi-C eclipsed conformation. The dihedral angle of H-CSi-Si is calculated to be 24.6° at the RHF/6-31G* level (25.7° at the RHF/LANL2DZ+p level). Each of the carbon atoms of the methyl groups is also surrounded by three nonbonded thioformylthio groups. After the bond model analyses, we found that hypercoordination to the saturated carbon atom is essential for this unique geometry, as confirmed by scrutinizing the X-ray data of 1 .

Synthesis of a phosphine imide bearing a hydrosilane moiety, and its water-driven reduction to a phosphine

Organosilanes bearing a phosphine imide moiety were synthesized and crystallographically characterized. Reaction of the pentacoordinated hydrodiphenylsilyl derivative with water gave [2-(diphenylphosphino)phenyl]diphenylsilanol accompanied by both reduction of the phosphine imide moiety and hydrolytic oxidation of the Si-H moiety.

Cycloaddition reactions of an iminophosphorane bearing the Martin ligand with some double-bond compounds: syntheses, structures and thermolyses of a 1,3,2λ5-oxazaphosphetidine and a 1,3,2λ5-diazaphosphetidine-4-thione

Abstract Reactions of an iminophosphorane bearing the Martin ligand (2,4,6-Pr3iC6H2)(C6H4-2-C(CF3)2O)PNPh 1 with carbonyl compounds and phenyl isothiocyanate gave the corresponding [2+2]-cycloadducts, 1,3,2λ5-oxazaphosphetidine 2a and 1,3,2λ5-diazaphosphetidine-4-thione 8a, respectively, whose structures were characterized by X-ray crystallographic analyses. Thermolysis of cycloadduct 2a, which is considered as an intermediate of the aza-Wittig reaction, showed two reactivities giving cyclic phosphinate 4 and imine 5 as well as 1 and ketone 3, respectively. Thermolysis of 8a afforded not only 1 and phenyl isothiocyanate 7a, but also cyclic thiophosphinate 10 and diphenylcarbodiimide 11a. The formation of 10 and 11a suggests the bond recombination around phosphorus atom of 8a.

Synthesis of Four- and Five-Membered Heterocycles Derived from an Iminophosphorane

Reactions of an iminophosphorane bearing the Martin ligand with a ketone, an isothiocyanate, and an alkyne gave the corresponding cycloadducts, 1,3,2 u 5 -oxazaphosphetidine, 1,3,2 u 5 -diazaphosphetidine-4-thione, and 1,2 u 5 -azaphosphetine, respectively, while that with dimethyl acetylenedicarboxylate (DMAD) and successive hydrolysis afforded the 1,2 u 5 -oxaphosphole-(2 H )-one. Thermal reactions of the cycloadducts were also studied.