Ryo Shintani’s research while affiliated with Osaka University and other places

The mechanism of a copper‐catalyzed regio‐ and anti‐selective 1,2‐silylboration of internal alkynes was theoretically studied to understand the reaction pathway and the origin of selectivity. The proposed overall reaction pathway involves the syn‐to‐anti isomerization via an anionic allenic transition state stabilized by the conjugation with the benzene ring. The anti‐selectivity is determined at the borylation step and controlled by the steric effect of the silyl group introduced on the alkyne carbon. The computational results obtained in this study are highly informative for the development of new catalytic transformations involving syn/anti‐isomerization processes.

An overcrowded ethylene composed of electron‐donating anion, naphthoxide, and electron‐accepting cation, acridinium, has been synthesized. It is in equilibrium between a folded conformer having a smaller permanent dipole moment with visible light absorption and a twisted conformer having a larger permanent dipole moment with NIR light absorption. The overcrowded ethylene shows multiple NIR chromisms, such as solvatochromism, thermochromism, mechanochromism, vapochromism, halochromism, and amphoteric electrochromisms, which are caused by the conformational change between folded and twisted conformers or by controlling the energy difference between the HOMO of the donor moiety and the LUMO of the acceptor moiety. The small difference between the HOMO energy level of naphthoxide moiety and the LUMO energy level of acridinium moiety, and their weak interaction are crucial for NIR absorption and large dipole moment in the twisted conformer. The drastic change in the ratio of folded and twisted conformers by changing the polarity of solvents, the detection of CO2, and the disappearance of NIR absorption by electrochemical oxidation and reduction are noteworthy for this new type of organic dye.

An overcrowded ethylene composed of electron‐donating anion, naphthoxide, and electron‐accepting cation, acridinium, has been synthesized. It is in equilibrium between a folded conformer having a smaller permanent dipole moment with visible light absorption and a twisted conformer having a larger permanent dipole moment with NIR light absorption. The overcrowded ethylene shows multiple NIR chromisms, such as solvatochromism, thermochromism, mechanochromism, vapochromism, halochromism, and amphoteric electrochromisms, which are caused by the conformational change between folded and twisted conformers or by controlling the energy difference between the HOMO of the donor moiety and the LUMO of the acceptor moiety. The small difference between the HOMO energy level of naphthoxide moiety and the LUMO energy level of acridinium moiety, and their weak interaction are crucial for NIR absorption and large dipole moment in the twisted conformer. The drastic change in the ratio of folded and twisted conformers by changing the polarity of solvents, the detection of CO2, and the disappearance of NIR absorption by electrochemical oxidation and reduction are noteworthy for this new type of organic dye.

2-Silylaryl triflates such as 2-(trimethylsilyl)phenyl triflate, known as Kobayashi reagent, have been widely used as efficient aryne precursors in organic synthesis, and various synthetic transformations have been developed based on this approach to date. On the other hand, synthesis of new organosilicon compounds by retaining the silicon substituents of 2-silylaryl triflates without forming arynes could be regarded as another attractive way of utilizing these compounds. In particular, silicon-containing cyclic compounds are expected to be useful for various applications such as biologically active substances and optoelectronic materials. In this regard, we have been actively engaged in developing new synthetic methods of silacycles by palladium-catalyzed reactions of 2-silylaryl triflates without the formation of aryne intermediates. As a result, we have succeeded in the selective synthesis of various silacycles through the activation of C-H and/or C-Si bonds as well as their intramolecular bond exchange process with C-Pd bonds that are generated during the catalytic reactions. The target compounds of our reactions include silicon-stereogenic dibenzosiloles, highly substituted benzosilacyclobutenes, silicon-stereogenic 5,10-dihydrophenazasilines, benzophenanthrosilines, benzofluorenosilepins, silabenzoxazines, and tetrahydrophenanthrosiloles. Herein an overview of these transformations is described along with their mechanistic aspects. Graphical Abstract Fullsize Image

2-Silylaryl triflates are widely employed as effective aryne precursors in organic synthesis, but their use as substrates for the synthesis of organosilicon compounds by retaining their silicon substituents is another attractive usage of these reagents. In particular, cyclic compounds having a silicon atom in the ring are promising candidates for various biologically active substances and optoelectronic functional materials. In this context, new synthetic methods of silicon-containing cyclic compounds have been actively investigated through the development of palladium-catalyzed reactions of 2-silylaryl triflates without generating aryne intermediates. As a result, selective synthesis of various silacyclic compounds has been achieved via C–H and/or C–Si bond activations as well as intramolecular exchange between these bonds and C–Pd bonds that are formed as reaction intermediates. An overview of this topic is described including the mechanistic insights.

A KO t Bu-catalyzed ring-opening gem -silylborylation of cyclopropenes with silylboronates has been developed for the synthesis of (1-silyl)allylboronates, a useful class of compounds in organic synthesis. The reaction proceeds with high selectivity...

Single‐molecule junctions exploit the internal structure of molecular orbitals to construct a new class of functional quantum devices. The demonstration of negative differential resistance (NDR) in single‐molecule junctions is direct evidence of quantum mechanical tunneling through a molecular orbital. Here, a pronounced NDR effect is reported with a peak‐to‐valley ratio of 30.1 on a single‐molecule junction of π‐conjugated quinoidal‐fused oligosilole derivatives, Si2 × 2, embedded between the unique electroless gold‐plated heteroepitaxial spherical Au/Pt nanogap electrodes. This NDR feature persists in a consecutive endurance test of 180 current traces. the thermally stable NDR effects in the Si2 × 2 single‐molecule junctions between 9 and 300 K are demonstrated. The density functional theory calculations under electric fields indicate that the NDR effect can be ascribed to the bias‐dependent resonant tunneling transport via the polarized HOMO, which has asymmetrically changed electrode coupling with increased bias voltages. The results confirm a promising electrical platform for constructing functional quantum devices at the single‐molecule level.