Sabrina Fischer, Johannes Schmidt, P. Strauch
Nov 11, 2013
Citations
0
Influential Citations
118
Citations
Quality indicators
Journal
Angewandte Chemie
Abstract
Salts and complexes of weakly coordinating anions (WCAs) have found promising applications as catalysts and superacids, and for the preparation of highly active organometallic compounds. Tetrakis(pentafluorophenyl)borate is such a WCA which has been frequently described and applied, for example recently as a building block in dendrimers. The structurally related, but uncharged, tetraphenylmethane is a suitable tecton for the generation of microporous polymer networks; when it is functionalized with polymerizable groups, the resulting networks sometimes display extraordinarily high surface areas. Furthermore it has been shown that the central carbon atom can be replaced by other elements such as silicon to form element–organic frameworks. In this context a functionalized tetraphenylborate anion should be suitable for the formation of microporous polymer networks. This type of material—microporous anionic borate networks (ABNs)—would combine the field of WCAs with the field of microporous polymer networks. In this material it can be assumed that due to the microporous architecture the countercation would be mobile and fully accessible even in the solid state, comparable to the extra-framework cations in inorganic zeolites. As the nonfluorinated tetraphenylborate anion shows limited chemical and photochemical stability, we used a more common fluorinated compound with a suitable functional group for polymerization, namely lithium tetrakis(4-bromo-2,3,5,6-tetrafluorophenyl)borate (Li[B(C6F4Br)4]), as the tecton in this work (for the synthetic protocol and analysis of this tecton, see Figures S1–S5 in the Supporting Information). Recently bromo-functionalized tetraphenylphosphonium has been reported as a tecton, which in principle would yield the cationic counterpart to our proposed anionic networks. Yamamoto coupling was applied to couple these tectons, yielding a mixture of phosphonium and phosphine moieties within the polymer. Likewise all our attempts to directly couple Li[B(C6F4Br)4] by Yamamoto coupling failed; we obtained networks with variable amounts of borate and borane moieties in low yields. Therefore we copolymerized Li[B(C6F4Br)4] with 1,3,5-triethynylbenzene using Sonogashira coupling (Scheme 1).