Highly Efficient Synthesis of Poly(silylether)s: Access to Degradable Polymers from Renewable Resources

Electrophilic Hydrosilylation of Electron-Rich Alkenes Derived from Enamines

The low-electron count, air-stable, platinum complexes [Pt(ItBu')(ItBu)][BArF] (C1) (ItBu=1,3-di-tert-butylimidazol-2-ylidene), [Pt(SiPh)3(ItBuiPr)2][BArF] (C2) (ItBuiPr=1-tert-butyl-3-iso-propylimidazol-2-ylidene), [Pt(SiPh)3(ItBuMe)2][BArF] (C3), [Pt(GePh3)(ItBuiPr)2][BArF] (C4), [Pt(GePh)3(ItBuMe)2][BArF] (C5) and [Pt(GeEt)3(ItBuMe)2][BArF] (C6) (ItBuMe=1-tert-butyl-3-methylimidazol-2-ylidene) are efficient catalysts (particularly the germyl derivatives) in both the silylative dehydrocoupling and hydrosilylation of electron rich alkenes derived from enamines. The steric hindrance exerted by the NHC ligand plays an important role in the selectivity of the reaction. Thus, bulky ligands are selective towards the silylative dehydrocoupling process whereas less sterically hindered promote the selective hydrosilylation reaction. The latter is, in addition, regioselective towards the β-carbon atom of both internal and terminal enamines, leading to β-aminosilanes. Moreover, the syn stereochemistry of the amino and silyl groups implies an anti Si-H bond addition across the double bond. All these facts point to a mechanistic picture that, according to experimental and computational studies, involves a non-classical hydrosilylation process through an outer-sphere mechanism in which a formal nucleophilic addition of the enamine to the silicon atom of a platinum σ-SiH complex is the key step. This is in sharp contrast with the classical Chalk-Harrod mechanism prevalent in platinum chemistry.

Acid-Catalyzed Activation and Condensation of the =C5H Bond of Furfural on Aldehydes, an Entry Point to Biobased Monomers

Furfural is an industrially relevant biobased chemical platform. Unlike classical furan, or C-alkylated furans, which have been previously described in the current literature, the =C5H bond of furfural is unreactive. As a result, on a large scale, C=C and C=O bond hydrogenation/hydrogenolysis is mainly performed, with furfuryl alcohol and methyl tetrahydrofuran being the two main downstream chemicals. Here, we show that the derivatization of the -CHO group of furfural restores the reactivity of its =C5H bond, thus permitting its double condensation on various alkyl aldehydes. Overcoming the recalcitrance of the =C5H bond of furfural has opened an access to a biobased monomer, whose potential have been investigated in the fabrication of renewably-sourced poly(silylether). By means of a combined theoretical-experimental study, a reactivity scale for furfural and its protected derivatives against carbonylated compounds has been established using an electrophilicity descriptor, a means to predict the molecular diversity and complexity this pathway may support, and also to de-risk any project related to this topic. Finally, by using performance criteria for industrial operations in the field of fuels and commodities, we discussed the industrial potential of this work in terms of cost, E-factor, reactor productivity and catalyst consumption.

Poly(silyl ether)s as Degradable and Sustainable Materials: Synthesis and Applications

Polymer research is currently focused on sustainable and degradable polymers which are cheap, easy to synthesize, and environmentally friendly. Silicon-based polymers are thermally stable and can be utilized in various applications, such as columns and coatings. Poly(silyl ether)s (PSEs) are an interesting class of silicon-based polymers that are easily hydrolyzed in either acidic or basic conditions due to the presence of the silyl ether Si-O-C bond. Synthetically, these polymers can be formed in several different ways, and the most effective and environmentally friendly synthesis is dehydrogenative cross coupling, where the byproduct is H2 gas. These polymers have a lot of promise in the polymeric materials field due to their sustainability, thermal stability, hydrolytic degradability, and ease of synthesis, with nontoxic byproducts. In this review, we will summarize the synthetic approaches for the PSEs in the recent literature, followed by the properties and applications of these materials. A conclusion and perspective will be provided at the end.

Iron-Catalyzed Alkoxylation, Dehydrogenative-Polymerization and Tandem Hydrosilylative-Alkoxylation

Alkoxylation, hydrosilylative-alkoxylation, and dehydrogenative-polymerization are some of the most widely used transformations in synthetic chemistry. However, these transformations are traditionally catalyzed by precious, and rare late-transition metals. Presented here is a molecularly defined iron complex that catalyzes alkoxylation, tandem hydrosilylative-alkoxylation, and dehydrogenative polymerization of silanes under mild conditions. The iron complex [Fe(CO)4 (H)(SiPh3 )] 1 catalyzes a direct Si-O coupling reaction between an array of silanes and alcohols to produce desired alkoxysilanes in excellent yield, with H2 as the only byproduct. The iron catalyst tolerates various functional groups and provides access to 20 alkoxysilanes, including essential molecules such as β-citronellol and cholesterol. Further, complex 1 catalyzes the polymerization of renewable diol and silane monomer to produce a renewable and degradable poly(isosorbide-silyl ether). Remarkably, complex 1 catalyzes a tandem hydrosilylative-alkoxylation of alkynes under mild conditions to yield unsaturated silyl ethers. The synthetic utility has been demonstrated by gram-scale alkoxylation and hydrosilylative-alkoxylation reactions.

Depolymerization of robust polyetheretherketone to regenerate monomer units using sulfur reagents

Super engineering plastics, high-performance thermoplastic resins such as polyetheretherketone, and polyphenylene sulfide have been utilized in industries, owing to their high thermal stability and mechanical strength. However, their robustness hinders their depolymerization to produce monomers and low-weight molecules. Presently, chemical recycling for most super engineering plastics remains relatively unexplored. Herein, we report the depolymerization of insoluble polyetheretherketone using sulfur nucleophiles via carbon-oxygen bond cleavages to form benzophenone dithiolate and hydroquinone. Treatment with organic halides converted only the former products to afford various dithiofunctionalized benzophenones. The depolymerization proceeded as a solid-liquid reaction in the initial phase. Therefore, this method was not affected by the shape of polyetheretherketone, e.g., pellets or films. Moreover, this depolymerization method was applicable to carbon- or glass fiber-enforced polyetheretherketone material. The depolymerized product, dithiofunctionalized benzophenones, could be converted into diiodobenzophenone, which was applicable to the polymerization.

Orthogonally deconstructable and depolymerizable polysilylethers via entropy-driven ring-opening metathesis polymerization

The synthesis of novel polysilylethers via entropy-driven ring-opening metathesis polymerization (ED-ROMP) of cyclic bifunctional silyl ether-based monomers is reported. These polymers display good thermal stability and ultra-low T_g (-88 °C). Moreover, they are rapidly deconstructable via the cleavage of the silicon-oxygen linkages with acid or fluoride triggers, and they were partially depolymerizable by the addition of exogenous metathesis catalyst. Analysis of the deconstructed polymer products provided insight into the polymer microstructure, showing that the ED-ROMP process was regiorandom. Altogether, this work offers a new class of deconstructable polymers with a range of potential applications.

Controllable Degradation of Polyurethane Thermosets with Silaketal Linkages in Response to Weak Acid

Polyurethane (PU) thermosets offer great favors to our daily life on account of their excellent mechanical, physical, and chemical properties as well as appreciable biocompatibility. Nevertheless, PU waste is increasingly causing environmental and health-related problems as it is mostly resistant to chemical degradation under mild conditions. Herein, we report a kind of PU thermoset with silaketal leakages in its main chains to enable polymer degradation in response to weak acids, even in edible vinegar. The degradation rate is significantly influenced by the alkyl substituents on the silicon atoms, with entire degradation in hours, days, weeks, or months. Besides controllable degradation, investigations are also provided into the recycling of PU thermosets by means of thermal reprocessing based on carbamate bond exchange or repolymerization of degradation residuals. Because of the controllable degradation and easy recycling, this particular kind of PU thermoset exhibits great potential in manufacturing green polymer products that can be decomposed by nature or reutilized after disposal.

2,5-Furandicarboxylic Acid: An Intriguing Precursor for Monomer and Polymer Synthesis

The most versatile furanic building block for chemical and polymer applications is 2,5-furandicarboxylic acid. However, the classical 2,5-furandicarboxylic acid production methodology has been found to have significant drawbacks that hinder industrial-scale production. This review highlights new alternative methods to synthesize 2,5-furandicarboxylic acid that are both more advantageous and attractive than conventional oxidation of 5-hydroxymethylfurfural. This review also focuses on the use of 2,5-furandicarboxylic acid as a polymer precursor and the various potential applications that arise from these furan-based materials.