Iterative Synthesis of Oligosilanes Using Methoxyphenyl- or Hydrogen-Substituted Silylboronates as Building Blocks: A General Synthetic Method for Complex Oligosilanes

Facile Synthesis of Polyorganosiloxanes via Photo-Induced Anionic Ring-Opening Polymerization Using a Latent Catalyst

Precise, controlled, and living polymerization of cyclosiloxanes is garnering considerable attention due to the distinct properties and promising applications of polyorganosiloxanes in various fields. In this contribution, photo-induced living anionic ring-opening polymerization of cyclosiloxanes is achieved by developing an efficient photobase generator (PBG). Structure-photoactivity analysis of the photo-latent catalyst is undertaken by synergistic density functional theory (DFT) calculations and experimental investigations. DFT calculations predict the superior photoactivity of the synthesized PBG2 (i.e., 2-[(9-oxo-9H-thioxanthen-2-yl)oxy]acetic-1,5,7-riazabicyclo[4.4.0]dec-5-ene) and provide insights into the structure-catalytic activities, which is confirmed through the experiments. Polyorganosiloxanes with predetermined molar masses and low dispersities (Đ < 1.30) are produced through on-demand cleavage of PBG2 under various light intensities, different PBG2 loadings, and sequential addition of monomers. On-off light switching enables the polymerization in a rate-controlled manner. Later on, mechanistic insights by DFT calculations identify the anionic species for nucleophilic attack and reveal that the reversible equilibrium involving anionic species, catalyst cations, and ion pairs contributes to precise control over chain growth during photopolymerization. Furthermore, deterministic kinetic simulation disentangles the effects of the cleavage rate and loading of PBG2 on polymerization kinetic behaviors. This developed photopolymerization strategy shows promising potential to expand the application of polyorganosiloxanes in advanced manufacturing fields.

Recent advances and perspectives in synthetic applications of silylboronates as silyl radical precursors

Silylboronates, as powerful and versatile reagents, have been widely used in synthetic chemistry over the past few decades, due to their ability to incorporate silicon and boron atoms into organic molecules. With the rapid development of radical chemistry, the use of silylboronates as silyl radical precursors has recently become a research focus in organic synthesis. Significant achievements have been made in the synthetic applications of silylboronates as silyl radical sources for various C-Si and C-X bond forming transformations. This review summarizes these recent advances, discusses their advantages and limitations, and illustrates the synthetic chances still open for further research and applications in this emerging area.

Precise Synthesis of Complex Si-Si Molecular Frameworks

In this Perspective, we highlight the emergence of target-oriented syntheses of complex molecules composed of Si-Si (oligosilanes) rather than C-C bonds. Saturated oligosilanes structurally resemble alkanes with respect to a tetrahedral geometry, a preference for a staggered conformation in linear chains, the ability to form stable small rings, and tetrahedral stereochemistry at asymmetrically functionalized Si centers. There are also critical differences, for example, differences in multiple bonding and the ability to form penta- and hexacoordinated structures, that mean that chemical reactivity and, in particular, rules for stereoselective synthesis do not cleanly translate from carbon to silicon. This Perspective will discuss recent achievements in the precise, controlled synthesis of complex molecules comprised mainly of Si-Si bonds and highlight the mechanistic insights enabling increased molecular complexity. New tools, such as electrochemical and catalytic reactions, will be discussed as well as the problem of controlling relative configuration in molecules containing multiple stereogenic-at-silicon centers. These synthetic achievements facilitate the discovery of new properties, including insight into light absorption, conformation, and mechanical properties.

Isolable Si=B Analogue of a Vinyl Halide: A Building Block for Facile Access toward Silicon-Boron Multiple Bonded Species

Compared to the outstanding development in the synthesis of Si-B single bonded species, borylsilanes and their application to organic synthesis, the chemistry of Si=B double bonded species, borasilenes and boratasilenes have only made little progress, first of all, due to the difficulties in accessing such double bonds. Herein we report the synthesis of the first Si=B analogue of a vinyl halide, a bromoboratasilene, via formal borylene insertion to the coordination sphere of a monoatomic Si(0) complex, using a dihaloborane as the borylene source. The treatment of bromoboratasilene toward neutral or anionic Lewis bases gives access to new boratasilenes, all of which were proved to possess significant Si=B double bond character by XRD analysis and DFT calculations. These results demonstrate exciting strategies to synthesize new types of Si=B double bonded species which should further progress the chemistry of boron, silicon-containing molecules.

Iterative SuFEx approach for sequence-regulated oligosulfates and its extension to periodic copolymers

The synthesis of sequence-regulated oligosulfates has not yet been established due to the difficulties in precise reactivity control. In this work, we report an example of a multi-directional divergent iterative method to furnish oligosulfates based on a chain homologation approach, in which the fluorosulfate unit is regenerated. The oligosulfate sequences are determined by high resolution mass spectrometry of the hydrolyzed fragments, and polysulfate periodic copolymers are synthesized by using oligomeric bisfluorosulfates in a bi-directional fashion. The synthetic utility of this iterative ligation is demonstrated by preparing crosslinked network polymers as synthetic adhesive materials.