Generation and Applications of the Hydroxide Trihydrate Anion, [OH(OH2)3]−, Stabilized by a Weakly Coordinating Cation

Abstract 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.


General Part
All chemicals were obtained from commercial sources and used without further purification. Standard high-vacuum techniques were employed throughout all preparative procedures, except aqueous workups. Non-volatile compounds were handled in a dry N2 atmosphere using Schlenk techniques.

NMR Spectroscopy
NMR spectra were recorded on a Bruker Model Avance III 300 spectrometer ( 1 H 300.13 MHz; 13 C 75.47 MHz; 19 F 282.40 MHz; 31 P 121.49 MHz). Positive shifts are downfield from the external standards TMS ( 1 H, 13 C), CCl3F ( 19 F) and H3PO4 ( 31 P). The NMR spectra were recorded in the indicated deuterated solvent or in relation to acetone-d6-filled capillaries.

IR Spectroscopy
IR spectra were recorded on an ALPHA-FT-IR spectrometer (Bruker) using an ATR unit with a diamond crystal for liquids and solids.

Melting Point
Melting points were measured on a Mettler Toledo Mp70 Melting Point System. 2

Synthesis of (Et2N)3PNH (4)
Phosphorus pentachloride (29.62 g, 142.2 mmol) is suspended in 250 mL of dichloromethane at -78 °C. A solution of diethylamine (6.6 eq, 98.0 mL, 944 mmol) in 50 mL of dichloromethane is added dropwise, so that the inner temperature is kept below -30 °C. After the addition, the orange slurry is allowed to warm to room temperature. After an additional hour of stirring, the mixture is cooled to -20 °C and gaseous ammonia is bubbled into the reaction mixture via a syringe over a period of 50 minutes. After positive 31 P NMR control, the suspension is filtrated over a Schlenk frit and the colorless solid is washed with dichloromethane (3 x 25 mL). The solvent is removed under reduced pressure, leading to a hygroscopic orange solid (60.78 g), containing diethylammonium chloride. The product is dissolved in 60 mL of methanol at -20 °C and a solution of potassium-tert-butanolate (65.85 g, 586.9 mmol) in 150 mL of methanol is added dropwise to the orange solution. After addition, the mixture is allowed to warm to room temperature and stirred overnight. The precipitate is filtered off and washed with methanol (3 x 20 mL). The filtrate is freed from solvent under reduced pressure. All volatile components are condensed into a second Schlenk flask (110 °C, 10 -3 mbar). The yellow solution is distilled in vacuo, leading to a pale yellow liquid (32.39 g, 123.5 mmol, 87 % based on PCl5, 10 -3 mbar, 60-82 °C).

Synthesis of Cl3PNtBu (5)
Phosphorus pentachloride (31.53 g, 151.5 mmol) is suspended in 750 mL of n-pentane before a solution of tert-butylamine (3.1 eq, 34.34 g, 469.5 mmol) in 150 mL of npentane is added dropwise under ice bath cooling. Thereafter the suspension is refluxed for 1.5 h and then stirred overnight at room temperature. The precipitate is
The column is washed two times with 30 mL of a methanol / water mixture (7 : 3). The   In a cooling bath the suspension is allowed to warm to -70 °C and then a catalytic amount of iron(III)nitrate nonahydrate is added. The blue suspension is stirred for

h, until the suspension changed color from deep blue to brown. Then [3H]Cl
(18.45 g, 20.0 mmol) is added and the suspension is allowed to warm to room temperature in the cooling bath overnight. The solid is suspended in 60 mL of nhexane and the slurry is filtrated over a Schlenk-frit (P4). The residue is washed two times with 10 mL of n-hexane. The solvent is removed from the combined filtrates to give 3 (16.19 g, 18.7 mmol, 94 %) as a bright yellowish solid.

Synthesis of Me3SiCF3 and exemplary regeneration of 3
In a flame-dried flask equipped with a Young valve a sample of 3 (5.39 g, 6.08 mmol) is dissolved in 20 mL of n-hexane. The solution is degassed three times. Fluoroform   acetone-d6 in a capillary.

Synthesis of Me3SiC2F5
In

Details on the X-Ray Diffraction
The crystal data were collected on a Rigaku Supernova diffractometer using graphitemonochromated Mo-Kα radiation (l = 71.073 pm) or Cu-Kα radiation (l = 154.184 pm) at 100.0(2) K.
Using Olex2 [2] , the structures were solved with the ShelXS [3] structure solution program using direct methods and refined with the ShelXL [4] refinement package using least squares minimization. Details of the X-ray investigation are given in Table 2. CCDC 1938109 -1938111 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html.