Tuneable, Protected and Processable Polystannanes from a Pincer Platform

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We have recently demonstrated a successful strategy employing hyper-coordinate (5-coordinate) tin centers that have led to the first examples of light and moisture stable tin polymers. This was achieved by incorporating ligands with pendant functionalities that serve as additional 2e- donors; increasing the coordination number at tin and providing a structural shield to nucleophilic attack, moderating the Lewis acidity at the metal and strengthening the sigma-sigma bonds with additional electron density sharing between adjacent tin centers. In several instances, these stable polymers are semi-crystalline and become difficult to process once purified. To enhance the overall design, a pincer ligand architecture with the potential to make three meridional interactions with the tin center and modified with solubilizing groups, is proposed. The 6e- donor nature of this ligand provides ideal structural protection and electron availability to the tin backbone. To prepare polymers, Sn(IV) dihalide (Br, I) intermediates will be accessed from oxidative addition of Sn(II) pincer species, or directly from transmetallation reactions of lithiated pincer ligands with RSnCl3 (R = alkyl, aryl), or alternatively from redistribution reactions of triphenyl containing Sn(IV) pincer small molecules and SnCl4. Density functional theory (DFT) modelling of the small molecule and oligomer pincer species will be used to compare structural fits to X-ray data, probe Sn-Sn bonding, and predict 119Sn NMR chemical resonances. New Pincer containing polystannanes will be prepared from the dehydrogenative coupling of the tin dihydrido species and evaluated. The unique bonding arrangement of pincer containing polystannanes provides numerous access points to tune the band gap of these intrinsic conducting materials, increase film-forming properties and ensure processability via solubilizing long chain alkyl or alkoxy moieties. The performance of these moisture and light stable pincer polystannanes will be evaluated for potential uses as 3D-printable polymeric wires in molecular based electronics.