Rebekka S. Klausen

The first conjugated polymers with functional Si–Si crosslinks are reported. In addition to complete structural characterization using solid-state NMR techniques, the electronic structure of the polymers are supported by electrochemical studies.

The synthesis of a trifunctional cyclohexasilane affords branched poly(cyclosilanes).

Saurabh S. Chitnis, Rebekka S. Klausen and Erin M. Leitao introduce the Polymer Chemistry themed collection on hybrid inorganic–organic polymers.

Organoboranes hold an undeniable value in modern organic chemistry and show ever-growing potential in polymer design and functionalization. Azaborines, in particular, are still being explored as a promising class of organoboron compounds. We investigated the reactivity of a 1,2-azaborine towards Matteson homologation, a cornerstone of organoborane transformations. The azaborine was shown to be reactive towards nucleophiles. Addition of n-BuLi led to exchange of the R group, while addition of chloromethyllithium formed the desired tetracoordinate intermediate. However, rather than homologation, the complex readily underwent ring expansion via migration of the adjacent C(sp²), followed by deborylation. Computational analysis revealed a stable geometry of the azaboronate in which the migrating carbon is antiperiplanar to the leaving group, and which we propose as being responsible for the observed reactivity. This finding suggests a unique role for azaborines in molecular transformations which may be unachievable with other organoboron frameworks.

Stereoregularity in carbon-based polymers impacts critical physical properties such as crystallinity, but achieving comparable precision in polysilanes remains challenging. Herein, we report the synthesis of hybrid σ,π-conjugated polysilanes with defined stereoregularity, derived from cis- and trans-cyclosilane building blocks. Using Kumada polycondensation, we accessed a series of atactic, trans-enriched, and cis-enriched polysilanes, enabling a systematic investigation of how tacticity influences thermal and optical properties. Differential scanning calorimetry revealed distinct glass transition behaviors for stereoregular polymers compared to their atactic counterpart, and UV-vis spectroscopy demonstrated enhanced spectral resolution upon annealing of stereoregular films. A linear silane-based analog further underscored the structural impact of cyclic stereogenic units. These findings highlight how stereochemical precision in silicon-containing backbones can modulate macromolecular properties, opening avenues for the rational design of stereoregular polysilanes.

We report the synthesis of five new examples of ladder cyclohexasilanes, possessing up to three consecutive fused rings and differing in relative ring fusion configuration and side chain structure. By coupling a 1,4‐dipotassiooligosilyl dianion to a cyclohexasilane, we obtained bi‐ and tricyclic ladder cyclohexasilanes. Combined experimental and theoretical studies suggested that annulation could favor the cis configuration under kinetic control, while the trans configuration predominates under thermodynamic control. Computational studies show that with each additional ring in the trans‐diastereomeric series, the predicted onset of light absorption shifts to longer wavelengths.

We report the synthesis of five new examples of ladder cyclohexasilanes, possessing up to three consecutive fused rings and differing in relative ring fusion configuration and side chain structure. By coupling a 1,4‐dipotassiooligosilyl dianion to a cyclohexasilane, we obtained bi‐ and tricyclic ladder cyclohexasilanes. Combined experimental and theoretical studies suggested that annulation could favor the cis configuration under kinetic control, while the trans configuration predominates under thermodynamic control. Computational studies show that with each additional ring in the trans ‐diastereomeric series, the predicted onset of light absorption shifts to longer wavelengths.

The direct synthesis of Si–Si dimeric 9-dimethylsilafluorene, structural characterization via single crystal X-ray diffraction studies, and electrochemical redox chemistry with DFT electronic structural analysis is reported herein.

The tearing of a polymer network arises from mechanochemically coupled bond-breaking events in the backbone of a polymer chain. An emerging research area is the identification of molecular strategies for network toughening, such as the strategic placement of mechanochemically reactive groups (e.g., scissile mechanophores) in the crosslinks of a network instead of in the load-bearing primary strands. These mechanically labile crosslinkers have typically relied on release of ring strain or weak covalent bonds for selective covalent bond scission. Here, we report a novel chemical design for accelerated mechanochemical bond scission based on replacing a single carbon atom in a crosslinker with a silicon atom. This single-atom replacement affords up to a two-fold increase in the tearing energy. We suggest a mechanism, validated by computational modeling, for accelerated mechanochemical Si-C bond scission based on minimizing the energy required to distort the starting material toward the transition-state geometry. We demonstrated the seamless incorporation of these scissile carbosilanes to toughen 3D-printed networks, which demonstrates their suitability for additive manufacturing processes.