Abstract:We report on the first examples of isolated silanol–silanolate anions, obtained by utilizing weakly coordinating phosphazenium counterions. The silanolate anions were synthesized from the recently published phosphazenium hydroxide hydrate salt with siloxanes. The silanol–silanolate anions are postulated intermediates in the hydroxide‐mediated polymerization of aryl and alkyl siloxanes. The silanolate anions are strong nucleophiles because of the weakly coordinating character of the phosphazenium cation, which … Show more
“…TS-1 explains why TMDS 4 decreases the activation energy (see Table 1), since disilane 4 acts as a bidentate molecule for easily generating the cyclic intermediate. 26 If this is the case, 4 should have a rst order dependence in the rate equation, which is indeed observed in Fig. 5; the kinetics of the hydrosilylation of 1 with disilane 4 bearing two exible Si-H moieties close to each other, shows a much better rst order [silane] dependence, and 1 reacts much faster than monosilane 2.…”
The Pt–catalysed addition of silanes to functional groups such alkenes, alkynes, carbonyls and alcohols, i.e. the hydrosilylation reaction, is a fundamental transformation in industrial and academic chemistry, often claimed as...
“…TS-1 explains why TMDS 4 decreases the activation energy (see Table 1), since disilane 4 acts as a bidentate molecule for easily generating the cyclic intermediate. 26 If this is the case, 4 should have a rst order dependence in the rate equation, which is indeed observed in Fig. 5; the kinetics of the hydrosilylation of 1 with disilane 4 bearing two exible Si-H moieties close to each other, shows a much better rst order [silane] dependence, and 1 reacts much faster than monosilane 2.…”
The Pt–catalysed addition of silanes to functional groups such alkenes, alkynes, carbonyls and alcohols, i.e. the hydrosilylation reaction, is a fundamental transformation in industrial and academic chemistry, often claimed as...
“…Bulky phosphazenium cations are predestinated for the investigation of non‐coordinated anions, such as naked fluoride anions, [20] the hydroxide trihydrate anion [21] or reactive aluminates, [22] and are also capable to stabilize isolated silanol‐silanolate anions, as recently reported by us (Figure 1). [23] …”
The reaction of a saline phosphazenium hydroxide hydrate with siloxanes led to a novel kind of silanol‐silanolate anions. The weakly coordinating behavior of the cation renders the formation of silanol‐silanolate hydrogen bonds possible, which otherwise suffer from detrimental silanolate–oxygen cation interactions. We investigated the influence of various weakly coordinating cations on silanol‐silanolate motifs, particularly with regard to different cation sizes. While large cations favor the formation of intramolecular hydrogen bonds resulting in cyclic structures, the less bulky tetramethyl ammonium cation encourages the formation of polyanionic silanol‐silanolate chains in the solid state.
“…Das erhaltene kristalline Produkt 3, das aus dem gekühlten Reaktionsgemisch isoliert und durch Einkristall-Rçntgenbeugung analysiert wurde (Abbildung 1), zeigt ein Silanolat-Anion, das an zwei Silanolmoleküle gebunden ist. [25] Zur Erhçhung der Ausbeute von 3 wurde die Reaktion erneut mit der entsprechenden Stçchiometrie durchgeführt (Schema 3). [24] Verbindung 3 ist das erste Beispiel für ein isoliertes Silanol-Silanolat-Anion, das nicht in direktem Kontakt mit Gegenionen steht.…”
“…Ausgewählte Bindungslängen [pm] und Winkel [8]: O1-O4 242.9(2), O1-Si1 158.4(1), O4-Si3 157.8(1), O2-Si1 164.9(1), O2-Si2 162.1(1); O1-O4-Si3 125.1(1), O4-O1-Si1 119.0(1), O2-Si2-O3 112.3-(1). [25] Angewandte Chemie Zuschriften Anion in 2 sowie die Silanolat-Anionen in 3, 4 und 5 einen erhçhten nucleophilen Charakter auf. Dies wurde beispielhaft für das Silanolat-Salz 4 in der Depolymerisationsreaktion von Polydimethylsiloxan mit terminalen Trimethylsilyl-Gruppen gezeigt (Schema 5).…”
Wir berichten über die ersten Beispiele isolierter Silanol‐Silanolat‐Anionen unter Verwendung schwach koordinierender Phosphazenium‐Gegenionen. Die Silanolat‐Anionen wurden durch die Reaktion des kürzlich veröffentlichten Phosphazenium‐Hydroxid‐Hydrat‐Salzes mit Siloxanen synthetisiert. Die Silanol‐Silanolat‐Anionen sind postulierte Zwischenprodukte bei der Hydroxid‐vermittelten Polymerisation von Aryl‐ und Alkylsiloxanen. Die Silanolat‐Anionen sind wegen des schwach koordinierenden Charakters des Phosphazenium‐Kations starke Nucleophile. Diese Eigenschaft macht sich in ihrer Aktivität bei der Depolymerisation von Polysiloxanen bemerkbar.
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