Tomohiro Agou

Detection of Biologically Important Anions in Aqueous Media by Dicationic Azaborines Bearing Ammonio or Phosphonio Groups

New cationic triarylboranes bearing ammonio or phosphonio groups on the periphery were synthesized from a common intermediate, a dibromodibenzoazaborine. These cationic molecules are soluble in highly polar organic solvents as well as water, and they exhibit strong light absorption and photoluminescence emission in water. Complexation of the cationic azaborines with fluoride and cyanide ions in aqueous media proceeded and could be monitored by NMR, UV/Vis, and fluorescence spectroscopy.

Reactions of Diaryldibromodisilenes with N-Heterocyclic Carbenes: Formation of Formal Bis-NHC Adducts of Silyliumylidene Cations

Reactions of stable 1,2-dibromodisilenes ((E)-Ar(Br)Si=Si(Br)Ar) with N-heterocyclic carbenes (NHC) afforded NHC-arylbromosilylene adducts or bromide salts of the corresponding bis-NHC adducts of the formal arylsilyliumylidene cations ([ArSi:](+)). In some cases, an NHC was able to replace a bromide anion in the coordination sphere of the arylbromosilylene-NHC adduct.

Synthesis of Dibenzochalcogenaborins and Systematic Comparisons of Their Optical Properties by Changing a Bridging Chalcogen Atom

Novel hetero-pi-conjugated compounds (dibenzochalcogenaborins) with the same molecular framework, bearing a boron atom as an acceptor and chalcogen atoms as a donor, were synthesized, and systematic comparisons among these molecules were performed. X-ray crystallographic analysis of these molecules showed similar structures with high planarity. UV/Vis spectroscopy and theoretical calculations revealed that the absorption maxima and the HOMO-LUMO gap changed by systematically changing the bridging chalcogen atom. Dibenzooxaborin and dibenzothiaborin showed fluorescence emission both in solution and in the solid state with a small Stokes shift, indicating the high rigidity of these compounds. On the other hand, dibenzoselenaborin exhibited a very weak fluorescence as a result of the heavy atom effect.

Syntheses and Structures of an “Alumole” and Its Dianion

Base free: An alumole was synthesized and treatment with lithium afforded the lithium salt of the alumole dianion. The structures of these two molecules were then investigated. The C-C bond lengths of the AlC4 ring in the dianion are nearly equal. DFT calculations revealed that the 3p(Al)-π* conjugation lowers the LUMO level of the alumole and that coordination of two lithium cations to the alumole dianion results in a planar AlC4 ring.

Synthesis of kinetically stabilized 1,2-dihydrodisilenes.

Kinetically stabilized 1,2-dihydrodisilenes were successfully synthesized and isolated by the introduction of sterically protecting bulky aryl groups. These 1,2-dihydrodisilenes exhibit distinct Si═Si double-bond character in both solution and the solid state. The Si-H bonds in these 1,2-dihydrodisilenes exhibit higher s character than those of typical σ(4),λ(4)-hydrosilanes. Moderate heating of these 1,2-dihydrodisilenes in solution resulted in their isomerization to the corresponding trihydrodisilanes, with an intramolecular hydrogen migration as the rate-determining step.

Synthesis of π-Conjugated Dendrimers Based on Azaborines

pi-Conjugated dendrons and dendrimers based on dibenzoazaborine were synthesized. The azaborine dendrons exhibited strong light absorption and photoluminescence, reflecting the optical properties of the azaborine. The fluorescence from the azaborine dendrimers bearing a benzothiadiazole core was strongly red-shifted or quenched, indicating photoinduced electron transfer from the azaborine dendrons to the core unit.

Syntheses, optical properties, and theoretical investigation of silafluorenes and spirobisilafluorenes bearing electron-donating aminostyryl arms around a silafluorene core.

pi-Extended silafluorenes and spirobisilafluorenes bearing electron-donating aminostyryl substituents at the 2,7- or 3,6-positions were synthesized by a Horner-Wadsworth-Emmons reaction. The electronic influence of spirocyclic structure and substitution mode of the aminostyryl substituents was investigated by UV/Vis spectroscopy, which indicated the existence of a spiroconjugation effect in the 3,6-substituted spirobisilafluorene. They exhibited moderate to strong fluorescence emission, and the fluorescence properties were compatible with the UV/Vis absorption characteristics, except for the 3,6-substituted spirobisilafluorene, which showed relatively large enhancement of fluorescence quantum yield and Stokes shift. The influence of the spirocyclic structure and substitution mode on the photophysical properties of the silicon compounds was investigated by DFT calculations.

Syntheses and Structures of Terminal Arylalumylene Complexes

Terminal arylalumylene complexes of platinum [Ar-Al-Pt(PCy3 )2 ] (Ar=2,6-[CH(SiMe3 )2 ]2 C6 H3 (Bbp) or 2,6-[CH(SiMe3 )2 ]2 -4-(tBu)C6 H2 (Tbb)) have been synthesized either by the reaction of a dialumene-benzene adduct with [Pt(PCy3 )2 ], or by the reduction of 1,2-dibromodialumanes Ar(Br)Al-Al(Br)Ar in the presence of [Pt(PCy3 )2 ]. X-Ray crystallographic analysis reveals that the AlPt bond lengths of these arylalumylene complexes are shorter than the previously reported shortest AlPt distance. DFT calculations suggest that the AlPt bonds in the arylalumylene complexes have a significantly high electrostatic character.

Development of a general route to periphery-functionalized azaborines and ladder-type azaborines by using common intermediates

Azaborines and ladder-type azaborines bearing various functional groups can be synthesized starting from common dibromo derivative intermediates, and among several substituents, the carbazol-9-yl group was shown to enhance the photo-luminescence quantum yield of the azaborines up to a value of unity.

Activation of Dihydrogen by Masked Doubly Bonded Aluminum Species

Activation of dihydrogen by masked dialumenes (Al=Al doubly bonded species) is reported. Reactions of barrelene-type dialumanes, which have the reactivity as masked equivalents of 1,2-diaryldialumenes ArAl=AlAr, with H2 afforded dihydroalumanes ArAlH2 at room temperature (Ar: bulky aryl groups). These dihydroalumanes form hydrogen-bridged dimers [ArHAl(μ-H)]2 in the crystalline state, while a monomer-dimer equilibrium was suggested in solution. The 1,2-diaryldialumenes generated from the barrelene-type dialumanes are the putative active species in the cleavage of H2 .