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We present the synthesis and characterization of fluorinated polymers based on P, B, Si, Sn and Ge as heteroatoms via Grignard activation. The polymers are microporous with hydrophobic surfaces. The borate-based polymer was successfully applied as solid acid catalyst in the esterification of acetic acid with ethanol.

Grignard synthesis of fluorinated nanoporous element organic frameworks based on the heteroatoms P, B, Si, Sn and Ge Recently, porous polymers have attracted considerable attention as highly versatile materials for adsorption, separation and storage of gases, in catalysis, for optoelectronic applications and energy storage. Especially, metal–organic frameworks (MOFs) and covalent organic frameworks (COFs) are of interest due to their high surface areas and pore volumes. In order to tune the surface polarity, porous ionic organic networks were reported. Depending on the desired properties such as porosity, polarity and functionality, these materials can be tailored for their application by varying the organic linker and connector element.

The utilization of fluorinated linkers was reported for different MOFs and a COF, showing enhanced properties in terms of stability, hydrophobicity, gas affinity and selectivity in comparison to their non-fluorinated materials. In continuation of our work on element organic frameworks (EOFs) with P, Si and Sn as connector elements, here we present the synthesis and characterization of respective fluorinated porous polymers with P, B, Si, Sn and Ge as heteroatoms. The catalytic application of the borate based polymer as solid acid catalyst was demonstrated in the esterification of acetic acid with ethanol as test reaction.

As the activation of the fluorinated biphenyl linker was not successful neither via lithiation as reported for the non-fluorinated linker nor via classical Grignard reaction, a magnesium-halogen exchange was applied. The linker 4,4′-dibromooctafluorbiphenyl was activated twofold with isopropylmagnesium chloride lithium chloride (turbo Grignard) and subsequent reaction with the respective element chlorides in a one-pot procedure (Scheme 1) resulted in the fluorinated polymers EF-EOF (E = P, B, Si, Sn, Ge). (Perfluorophenyl)-magnesium bromide was used for end-capping, converting remaining E–Cl bonds into E–Ar bonds to form fully substituted trivalent or tetravalent centers, respectively. In all cases, the resulting polymers were obtained as fluffy white powders.