Rare-Earth-Catalyzed Selective Synthesis of Linear Hydridopolycarbosilanes and Their Functionalization

Advances in the Synthesis of Preceramic Polymers for the Formation of Silicon-Based and Ultrahigh-Temperature Non-Oxide Ceramics

Preceramic polymers (PCPs) are a group of specialty macromolecules that serve as precursors for generating inorganics, including ceramic carbides, nitrides, and borides. PCPs represent interesting synthetic challenges for chemists due to the elements incorporated into their structure. This group of polymers is also of interest to engineers as PCPs enable the processing of polymer-derived ceramic products including high-performance ceramic fibers and composites. These finished ceramic materials are of growing significance for applications that experience extreme operating environments (e.g., aerospace propulsion and high-speed atmospheric flight). This Review provides an overview of advances in the synthesis and postpolymerization modification of macromolecules forming nonoxide ceramics. These PCPs include polycarbosilanes, polysilanes, polysilazanes, and precursors for ultrahigh-temperature ceramics. Following our review of PCP synthetic chemistry, we provide examples of the application and processing of these polymers, including their use in fiber spinning, composite fabrication, and additive manufacturing. The principal objective of this Review is to provide a resource that bridges the disciplines of synthetic chemistry and ceramic engineering while providing both insights and inspiration for future collaborative work that will ultimately drive the PCP field forward.

Anionic stitching polymerization of styryl(vinyl)silanes for the synthesis of sila-cyclic olefin polymers

Anionic stitching polymerization of styryl(vinyl)silanes has been developed for the synthesis of a new type of silicon- and carbon-containing polymer possessing fused sila-bicyclic structures in the main chain. The obtained polymers were found to be thermally stable with relatively high glass-transition temperatures and highly transparent in the visible light region.

Metal-Free Hydrosilylation Polymerization by Merging Photoredox and Hydrogen Atom Transfer Catalysis

Organosilicon compounds and polymers have found wide applications as synthetic building blocks and functional materials. Hydrosilylation is a common strategy toward the synthesis of organosilicon compounds and polymers. Although transition-metal-catalyzed hydrosilylation has achieved great advances, the metal-free hydrosilylation polymerization of dienes and bis(silane)s, especially the one suitable for both electron-rich and electron-deficient dienes, is largely lacking. Herein, we report a visible-light-driven metal-free hydrosilylation polymerization of both electron-rich and electron-deficient dienes with bis(silane)s by using the organic photocatalyst and hydrogen atom transfer (HAT) catalyst. We achieved the well-controlled step-growth hydrosilylation polymerizations of the electron-rich diene and bis(silane) monomer due to the selective activation of Si-H bonds by the organic photocatalyst (4CzIPN) and the thiol polarity reversal reagent (HAT 1). For the electron-deficient dienes, hydrosilylation polymerization and self-polymerization occurred simultaneously in the presence of 4CzIPN and aceclidine (HAT 2), providing the opportunity to produce linear, hyperbranched, and network polymers by rationally tuning the concentration of electron-deficient dienes and the ratio of bis(silane)s and dienes to alter the proportion of the two polymerizations. A wide scope of bis(silane)s and dienes furnished polycarbosilanes with high molecular weight, excellent thermal stability, and tunable architectures.

Rare-Earth-Catalyzed Selective 1,4-Hydrosilylation of Branched 1,3-Enynes Giving Tetrasubstituted Silylallenes

Allenes are versatile synthons in organic synthesis and medicinal chemistry because of their diverse reactivities. Catalytic 1,4-hydrosilylation of 1,3-enynes may present the straightforward strategy for synthesis of silylallenes. However, the transition-metal-catalyzed reaction has not been successful due to poor selectivity and very limited substrate scopes. We report here the efficient and selective 1,4-hydrosilylation of branched 1,3-enynes enabled by the ene-diamido rare-earth ate catalysts using both alkyl and aryl hydrosilanes, leading to the exclusive formation of tetrasubstituted silylallenes. Deuteration reaction, kinetic study, and DFT calculations were conducted to investigate the possible mechanism, revealing crucial roles of high Lewis acidity, large ionic radius, and ate structure of the rare-earth catalysts.