Hajime Ito

Silicon-containing compounds are important in both academic and industrial settings, and the reductive coupling of chlorosilanes is a widely used approach for the formation of Si–Si bonds. However, despite its long history, this strategy for the formation of Si–Si bonds has remained largely limited to homocoupling, while a general synthetic method for selective heterocoupling has yet to be established. Previous strategies have relied on the stepwise generation of silicon nucleophiles or electrochemical methods. Here, we demonstrate that mechanochemical activation of strontium metal by ball milling enables the one-pot, cross-selective coupling of a broad range of chlorosilane pairs. Notably, after screening group 1 and group 2 metals, strontium was found to exhibit higher reactivity under mechanochemical conditions than commonly used metal reductants such as lithium and sodium. Importantly, no reaction occurs when strontium is employed under conventional solution conditions, highlighting the crucial role that mechanical activation plays in the reaction. Finally, this method is also applicable to the cross-coupling of chlorosilanes with chlorogermanes, thus establishing a practical and operationally simple protocol for the formation of E–E (E = Si, Ge) bonds.

A general method for generating functionalized arylsilyllithium species has been developed. The resulting silicon nucleophiles enable access to functionalized disilanes and oligosilanes beyond the scope of conventional chlorosilane reduction.

Silylenes are highly reactive divalent silicon species that enable diverse transformations via σ-insertion and π-addition to silylene acceptors, and thus represent key intermediates for the incorporation of silicon moieties into various chemical bonds. However, the practical use of silylenes as useful silicon synthons remains limited, as specific stabilizing substituents are currently required in order to suppress self-condensation and oligomerization. Herein, we report a novel strategy to generate diversely substituted silylenes through a reaction with an electron-deficient aryllithium to form boron-ate silylenoids derived from isolable chlorosilylborane precursors. Several chlorosilylboranes were readily prepared via the Si–H borylation of dialkylanisylsilanes and subsequent chlorination of the anisyl group, or via the monoborylation of dihydrosilanes followed by chlorination of the remaining hydride group. The generated silylenes exhibit the inherent reactivity associated with free silylenes, i.e., σ-insertions into Si–H bonds and π-additions to alkene and carbonyl compounds. Mechanistic studies revealed that the concentrations of the lithium silylenoid and the subsequent silylene remained lower than that of the boron-ate silylenoid due to the thermodynamic and kinetic unfavorability of the boron–lithium exchange. As a result of the low concentration of the generated silylene, it selectively reacts with the silylene acceptor rather than participating in side reactions such as self-condensation and oligomerization, which are problematic in the reduction of dichlorosilanes. Consequently, this work represents a reliable strategy to harness silylenes as versatile silicon synthons for transformations that are difficult to realize via the more conventional alkali-metal-mediated reduction of dihalosilanes.

We have developed the first mechanochemical protocol for a solvent-less palladium-catalyzed conjugate arylation, which was enabled by designing new mechanochemistry-directed bipyridine and chiral pyridine–oxazoline ligands.

An appropriate choice of milling conditions as well as a liquid-assisted grinding additive enable the Amano-PS-IM-catalyzed highly efficient acylative kinetic resolution of secondary alcohols under mechanochemical conditions.

Reactions involving both hydrophobic and hydrophilic molecules present a significant challenge due to the difficulties associated with finding solvents that are capable of effectively accommodating reactants with contrasting solubility properties. Solvent-free conditions offer a potential alternative, albeit that under conventional neat conditions, immiscible reactants often remain poorly mixed at the molecular level, resulting in low reactivity. Here, we demonstrate that mechanochemistry could potentially offer a practical solution to overcome this immiscibility issue. Specifically, we discovered that mechanical agitation by ball milling enables highly efficient Fischer glycosylation reactions of hydrophilic unprotected sugars with a wide range of hydrophobic long-chain aliphatic alcohols, offering straightforward access to various glycolipid derivatives. This type of direct glycosylation has been recognized as a challenging transformation due to the inefficient mixing of the immiscible substrate pairs under conventional conditions. Thus, the present study highlights the promising potential of a mechanochemical approach to tackle longstanding challenges associated with immiscibility in the synthesis of value-added amphipathic small molecules.

Rotational dynamics in molecular crystals influence not only internal structures but also bulk properties such as photophysical behavior. In this work, we present novel crystalline chiral binuclear N ‐heterocyclic carbene (NHC) Au(I) complexes, 1 ‐ R and 1 ‐ S , which display a distinct axially chiral conformation with C ₂ ‐symmetry, derived from non‐equivalent orientations of phenyl groups on the NHC ligands. These phenyl moieties undergo two distinct types of rapid rotational motion, as revealed by variable‐temperature solid‐state ² H NMR studies. Such dynamic motions promote structural symmetrization within the crystal, shifting from C ₂ ‐symmetry toward a more D ₂ ‐like symmetry. This symmetry evolution significantly affects the chiroptical properties of the crystals. Both experimental measurements and TD‐DFT calculations confirm that such motion modulates chiroptical properties, leading to temperature‐dependent changes in emission intensity and the luminescence dissymmetry factor ( g _lum ). These results highlight dynamic molecular rotation as a powerful tool for tuning symmetry and chiroptical responses in crystalline materials, offering new design principles for solid‐state chiral systems.

This study demonstrates the facile removal of benzyl-derived protecting groups via ammonia-free, mechanochemically driven Birch reduction using inexpensive and easy-to-handle sodium lumps. Various benzyl-protected alcohols and amines were efficiently deprotected within 30 min. Notably, all synthetic operations can be performed without inert gases or bulk solvents.

Trialkylsilyl substituents tune aryl–perfluoroaryl interactions, controlling crystal packing and solid-state photophysical properties.