Novel acrylate polymers functionalized with tetrafluorophenyl phosphonic acid groups were prepared by free radical polymerization of phosphonic ester acrylate monomers. Liberation of the free acid functions was realized by ester cleavage with Me3SiBr and the subsequent hydrolysis with methanol. The obtained polymers were analyzed by NMR and IR spectroscopy. The ion exchange capacity of the phosphonic acid functionalized methacrylate polymer was determined to 2.8 mmol/g by titration with 0.1 M NaOH. The proton conductivity under anhydrous conditions was determined to 6.84 x 10(-6) Scm(-1) at 120 degrees C by electrochemical impedance spectroscopy.

The renaissance of Brønsted superbases is primarily based on their pronounced capacity for a large variety of chemical transformations under mild reaction conditions. Four major set screws are available for the selective tuning of the basicity: the nature of the basic center (N, P, …), the degree of electron donation by substituents to the central atom, the possibility of charge delocalization, and the energy gain by hydrogen bonding. Within the past decades, a plethora of neutral electron-rich phosphine and phosphazene bases have appeared in the literature. Their outstanding properties and advantages over inorganic or charged bases have now made them indispensable as auxiliary bases in deprotonation processes. Herein, an update of the chemistry of basic phosphines and phosphazenes is given. In addition, due to widespread interest, their use in catalysis or as ligands in coordination chemistry is highlighted.

The superbasic tetraphosphazene is a thieving magpie on the hunt for the shiny proton. Phenols are readily deprotonated and the respective non-coordinated anions are formed in the presence of weakly Lewis-acidic phosphazenium counterions. Strongly nucleophilic non-coordinated phenolates excel as reducing agents for the generation of radical anion salts and for the activation of SF6. Their high Lewis-basicity is accompanied by a pronounced tendency for hydrogen bonding, which is perceptible in their chemical behavior. More information can be found in the Full Paper by B. Hoge et al. on page 6460.

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.

The non-coordinated phenolate anion ([H5C6-O]− is easily accessible by deprotonation of phenol with the superbasic perethyl tetraphosphazene Schwesinger base, while monophosphazenes only deliver the hydrogen-bonded phenol–phenolate adduct. Hydrogen bonding influences the electron donation and brings about lowered redox potentials. Synthesized electron-rich non-coordinated phenolates featuring strong redox potentials are capable for the SF6 activation and lead to pentafluorosulfanide [SF5]− salts. More information can be found in the Communication by B. Hoge et al. on page 6465.

In this work, the syntheses of non-coordinated electron-rich phenolate anions via deprotonation of the corresponding alcohols with an extremely powerful perethyl tetraphosphazene base (Schwesinger base) are reported. The application of uncharged phosphazenes renders the selective preparation of anionic phenol-phenolate and phenolate hydrates possible, which allows for the investigation of hydrogen bonding in these species. Hydrogen bonding brings about decreased redox potentials relative to the corresponding non-coordinated phenolate anions. The latter show redox potentials of up to -0.72(1) V vs. SCE, which is comparable to that of zinc metal, thus qualifying their application as organic zinc mimics. We utilized phenolates as reducing agents for the generation of radical anions in addition to the corresponding phenoxyl radicals. A tetracyanoethylene radical anion salt was synthesized and fully characterized as a representative example. We also present the activation of sulfur hexafluoride (SF6) with phenolates in a SET reaction, in which the nature of the respective phenolate determines whether simple fluorides or pentafluorosulfanide ([SF5](-)) salts are formed.

The reaction of the strong monophosphazene base with the weakly acidic phenol leads to the formation of a phenol-phenolate anion with a moderately strong hydrogen bond. Application of the more powerful tetraphosphazene base (Schwesinger base) renders the isolation of the corresponding salt with a free phenolate anion possible. This compound represents the first species featuring the free phenolate anion [H5C6-O](-). The deprotonation of phenol derivatives with tetraphosphazene bases represents a great way for the clean preparation of salts featuring free phenolate anions and in addition allows the selective syntheses of hydrogen bonded phenol-phenolate salts. This work presents a phosphazenium phenolate salt with a redox potential of -0.72 V and its capability for the selective activation of the chemically inert greenhouse gas SF6. The performed two-electron reduction of SF6 leads to phosphazenium pentafluorosulfanide ([SF5](-)) and fluoride salts.

AbstractWir 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.

AbstractDie Reaktion eines stark basischen Phosphazens (Schwesinger‐Base) mit Wasser lieferte das entsprechende metastabile Hydroxid‐Trihydrat‐Anion [OH(OH2)3]−. Dies ist das erste Hydroxid‐Solvat, das nicht mit einem Kation in Kontakt steht. Darüber hinaus stellt es eines der seltenen bekannten wasserstabilisierten Hydroxid‐Anionen dar. Die Thermolyse im Vakuum führt zur Zersetzung des Hydroxidsalzes und zur quantitativen Freisetzung der freien Phosphazenbase. Dieses Verhalten wurde für die Synthese der Schwesinger‐Base aus ihrem Hydrochloridsalz mit einem Anionenaustauscherharz in exzellenten Ausbeuten von über 97 % genutzt. Diese Deprotonierungsmethode kann auch für die phosphazenbasenkatalysierte Synthese des Ruppert‐Prakash‐Reagenzes Me3SiCF3 unter Verwendung von Fluoroform (HCF3) als Trifluormethylbaustein und Natriumhydroxid als formalem Deprotonierungsmittel verwendet werden.

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 is perceptible in their activity in polysiloxane depolymerization.

Das Hydroxid-Trihydrat-Anion konnte erstmals mithilfe eines schwach koordinierenden Phosphazenium-Kations generiert und strukturell charakterisiert werden, wie B. Hoge et al. in ihrer Zuschrift auf S. 14775 beschreiben. Im Bild wird das sterisch anspruchsvolle Phosphazenium-Kation als die Burgmauer zur Stabilisierung dieses seltenen Anions dargestellt, das sich wie eine empfindliche wässrige “Hydroxid-Seifenblase” leicht im Vakuum zersetzt.

The reaction of a strongly basic phosphazene (Schwesinger base) with water afforded the corresponding metastable hydroxide trihydrate [OH(OH2)(3)] salt. This is the first hydroxide solvate that is not in contact with a cation and furthermore one of rare known water-stabilized hydroxide anions. Thermolysis in vacuum results in the decomposition of the hydroxide salt and quantitative liberation of the free phosphazene base. This approach was used to synthesize the Schwesinger base from its hydrochloride salt after anion exchange in excellent yields of over 97%. This deprotonation method can also be used for the phosphazene-base-catalyzed preparation of the Ruppert-Prakash reagent Me3SiCF3 using fluoroform ( HCF3) as the trifluoromethyl building block and sodium hydroxide as the formal deprotonation agent.

The hydroxide trihydrate anion was generated for the first time and structurally characterized thanks to the use of a weakly coordinating phosphazenium counterion. As B. Hoge et al. describe in their Communication on page 14633 ff., the space-filling phosphazenium cation represents an impregnable castle wall in protecting and stabilizing this rare anion. Under vacuum, the salt decomposes like a fragile aqueous “hydroxide soap bubble”.