Masahiro Kako

Ionization and structural determination of the major isomer of Pr@C82

Abstract A stable diamagnetic mono-anion of the major isomer of Pr@C 82 (Pr@C 82 –A) was electrochemically prepared and isolated to determine the symmetry of its carbon cage. By measurement of the 13 C NMR spectrum of the anion, Pr@C 82 –A is found to have C 2v symmetry.

Two-step alkylation of single-walled carbon nanotubes: substituent effect on sidewall functionalization.

A two-step alkylation of single-walled carbon nanotubes was investigated. The functionalized SWNTs were characterized with vis-NIR and Raman spectrometers, scanning electron microscope, and thermogravimetric analysis. This one-pot alkylation of SWNTs with alkyllithium followed by alkyl halide is useful for the sidewall functionalization of SWNTs. This reaction shows significant substituent effects on the degree of functionalization of SWNTs. The degree of functionalization on SWNTs sidewall upon SWNTs may influence their characteristic properties on SWNTs sidewall by the substituent effects.

Photochemical addition of C60 with siliranes: synthesis and characterization of carbosilylated and hydrosilylated C60 derivatives.

Photochemical reactions of C(60) with siliranes (1a-d) afford adducts of four types (2a-5b) as carbosilylated and hydrosilylated C(60) derivatives. Characterization of these adducts was conducted using MS, UV, NMR spectroscopy, and single-crystal X-ray analyses. In particular, the first example of the crystal structure of a closed 1,2-adduct at the 5,6-ring junction of the C(60) cage is provided by single-crystal X-ray analysis of 3b. Electrochemical analyses also revealed unique redox properties of the products 2b-5b, which depend on the regiochemistry of the functionality, in addition to the substituents on the C(60) cage. Theoretical calculations offer bases for the experimentally observed redox properties and relative stabilities of the silylated products.

Thermal Carbosilylation of Endohedral Dimetallofullerene La2@Ih-C80 with Silirane

Thermal carbosilylation of endohedral dimetallofullerene La(2)@I(h)-C(80) with silirane (silacyclopropane) is reported herein for the first time. Two diastereomers of the carbosilylated La(2)@I(h)-C(80) have been isolated and characterized. The fascinating molecular structure of one diastereomer of the carbosilylated derivatives has been determined unambiguously using X-ray crystallographic analysis. Detailed characteristics of the molecular structures including their metal atom movements have also been revealed using NMR spectroscopic studies and computational calculations. Results revealed that two La atoms move dynamically inside the carbon sphere. Furthermore, electrochemical study has demonstrated that carbosilylation is effective to fine-tune the La(2)@I(h)-C(80) electronic properties.

Silylation of fullerenes with active species in photolysis of polysilane

Abstract Organosilicon compounds represent a unique feature of materials such as disilane and polysilane. Meanwhile, since the isolation of C60 and C70 in preparatively useful quantities, much attention has been devoted to chemical functionalization of these new allotropic forms of carbon, which continuously yields fascinating results. It can be expected that a combination of organosilicon compounds and fullerene forms a new class of organic compounds and at the same time opens a new field in material science. In this context, we have carried out the reaction of fullerenes with active species generated in photolysis of disilane and polysilane, by which we can obtain an attractive material and also clarify the chemical and electronic properties of fullerenes. We here summarize the recent advances in the chemistry of mono- and bis-silylation of fullerenes with silylene and silyl radical to afford the corresponding new fullerene-based organosilicon materials.

Analysis of Functionalization Degree of Single-Walled Carbon Nanotubes Having Various Substituents

Introducing substituents onto SWNT sidewalls increases their solubility and tunes their properties. Controlling the degree of functionalization is important because the addition of numerous functional groups on the sidewall degrades their intrinsic useful electronic properties. We examined the synthesis and characterization of sidewall-functionalized SWNTs in this study. The functionalized SWNTs ((1)R-SWNTs-(2)R) were prepared in a one-pot reaction of SWNTs with alkyllithium ((1)RLi) followed by alkyl bromide ((2)RBr). The functionalized SWNTs were characterized by the absorption and Raman spectroscopy and thermogravimetric analysis. Not only the total number of functional groups introduced on the SWNT sidewall (formula mass: (1)R = (2)R) but also the ratio of (2)R to (1)R in the functionalized SWNTs (formula mass: (1)R ≠ (2)R) having two different substituents were clarified using the relation between results of Raman spectroscopy and thermogravimetric analysis. Results show that the degree of functionalization of (2)R to (1)R in (1)R-SWNTs-(2)R can be well controlled by the bulkiness of the alkyl groups of (1)RLi and (2)RBr. Moreover, substituent effects of reductive alkylation and reductive silylation of SWNTs via Birch reduction were investigated.

Silylation of higher fullerenes

Photochemical silylations of higher fullerenes (C70, C76(D2), C84(D2)) are reported. During the photochemical cycloaddition of these higher fullerenes with disilirane, the formation of mono-adducts was observed. Since the highly selective disilirane addition to C70 was observed, the reaction of C76(D2) and C84(D2) with disilirane gave at least eight and seven isomers of the mono-adduct, respectively. These adducts were isolated in their pure form by multistage HPLC. The electronic properties of these adducts were also investigated using differential pulse voltammetry. The results indicate that silylation is very effective for producing the electronegative higher fullerene derivatives.

A 3,4-benzo-1,2-germacyclobut-3-ene and related compounds. Palladium-catalyzed σ-metathesis, dehydrogenative coupling and hydrogermylation of the GeGe σ-bond

Abstract In the presence of catalytic amounts of Pd(PPh3)4, 3,4-benzo-1,1,2,2-tetraethyl-1,2-germacyclobut-3-ene (1) readily undergoes the reversible σ-bond metathesis to give a dimer, 1,2,5,6-dibenzo-3,4,7,8-tetragermacycloocta-1,5-diene (6) below 100°C. However, at 160°C in toluene containing catalytic amounts of Pd(PPh3)4, both 1 and 6 afford an unsymmetrical dimer, 1,2,4,5-dibenzo-3,6,7,8-tetragermacycloocta-1,4-diene (8) with two isomeric products. In the presence of Pd(PPh3)4, 1,2-bis(diethylgermyl)benzene (18) undergoes dehydrocouling to give 1, which is smoothly converted to 6 under these conditions. The metal-metal σ-bonds of 1 and its silicon analogue are highly susceptible to hydrogermylation but not to hydrosilylation in the presence of Pd(PPh3)4.

Photo-induced electron transfer oxygenation of 1,2-disiletene☆

Abstract Photo-induced electron transfer oxygenation of 3-phenyl-1,1,2,2-tetramesityl-1,2-disilet-3-ene (1) in acetonitrile-methylene chloride afforded the corresponding 1,2-dioxa-3,6-disilin (2) in moderate yield as a dioxygen insertion product into a silicon-silicon σ-bond together with 1-oxa-2,5-disilolene (3). The results are reasonably accounted for by an electron transfer disiletene 1 to the excited singlet state of the sensitizer to form a radical ion pair followed by addition of oxygen. Interestingly, a remarkable solvent effect was observed in the product ratio of dioxadisilin 2 and oxadisilolene 3 as a monooxygenated product. The solvent acetonitrile, acting as a nucleophile, participates for predominant formation of 2. Meanwhile, in the absence of acetonitrile, 3 was afforded as a major product. The conceivable mechanism is proposed.

Bis-Silylation of Lu3N@Ih-C80: Considerable Variation in the Electronic Structures

Photochemical reactions of Lu(3)N@I(h)-C(80) with disiliranes 1 and 2 produce several isomeric adducts. Spectroscopic analyses characterize the most stable isomers as 1,4(AA) adducts, which consist of paired twist conformers at rt. The electrochemical and theoretical studies reveal that the HOMO-LUMO energy gaps of the 1,4(AA) adducts are smaller than that of Lu(3)N@I(h)-C(80) because the electron-donating groups effectively raise the HOMO levels.