Journal
ANGEWANDTE CHEMIE-INTERNATIONAL EDITION
Volume 60, Issue 17, Pages 9618-9626Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/anie.202015960
Keywords
acidity; silanes; silicon; strained molecules; zwitterions
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Funding
- NoNoMeCat Marie Skodowska-Curie training network - European Union [675020-MSCA-ITN-2015-ETN]
- Netherlands Organization for Scientific Research (NWO)
- SURF Foundation
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By introducing strain, a strained cationic silane [TSMPSiH](+) with unusual acidity was successfully prepared, showing correlations with ring strain, inductive and electrostatic effects. The conjugate base TSMPSi can activate a THF molecule in the presence of CH-acids to generate a highly fluxional alkoxysilane.
Compounds of main-group elements such as silicon are attractive candidates for green and inexpensive catalysts. For them to compete with state-of-the-art transition-metal complexes, new reactivity modes must be unlocked and controlled, which can be achieved through strain. Using a tris(2-skatyl)methylphosphonium ([TSMPH3](+)) scaffold, we prepared the strained cationic silane [TSMPSiH](+). In stark contrast with the generally hydridic Si-H bond character, it is acidic with an experimental pK(a)(DMSO) within 4.7-8.1, lower than in phenol, benzoic acid, and the few hydrosilanes with reported pK(a) values. We show that ring strain significantly contributes to this unusual acidity along with inductive and electrostatic effects. The conjugate base, TSMPSi, activates a THF molecule in the presence of CH-acids to generate a highly fluxional alkoxysilane via trace amounts of [TSMPSiH](+) functioning as a strain-release Lewis acid. This reaction involves a formal oxidation-state change from Si-II to Si-IV, presenting intriguing similarities with transition-metal-mediated processes.
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