Tetrabutylammonium tetrafluoroborate

TETRABUTYLAMMONIUM TETRAFLUOROBORATE AND BIS(4,4, 5,5 -TETRAMETHYL-2,2 -BI-l,3-DISELENOLYLIDENE) RADICAL ION (1-1-) TETRAFLUOROBORATE 

Submitted by ANN E. REHAN, ROBERT A. BARKHAU, and JACK M. WILLIAMSt Checked by MARSHA M. LEEf 

Initially, 1.67 mL of hydrogen tetrafluoroborate (48 wt % in HjO) [Aldrich] in 10 mL of distilled water is added dropwise (plastic syringe) with stirring (Teflon stir bar) to 22.78 mL of tetrabutylammonium hydroxide (40 wt % in H4O) [Aldrich] in a polyethylene beaker. A white precipitate, tetrabutylammonium tetrafluoroborate, forms immediately. The mixture is allowed to stir for 15 min and then cooled to 0° for 1 hr. The product is removed by Altering (polyethylene funnel and Alter flask) and is dried in a desiccator (plastic) over CaS04 for 12 hr. The Altrate is concentrated under vacuum to give additional product. The 

Recrystallization from water or aqueous ethanol, or ethyl acetate/pentane, or pure ethyl acetate with cooling in dry ice to induce precipitation, followed by drying at 80 °C under vacuum. 

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Tetranuclear iron-sulfur clusters of the type [Fe4S4(SR)4]2, where R = CH2C6H5 and C6H5, were found138 to catalyze the reduction of C02 in DMF solutions. Controlled-potential electrolyses were carried out in a C02-saturated 0.1 M tetrabutylammonium tetrafluoroborate (TBAT)-DMF solution at a mercury pool cathode. In the absence of a catalyst, C02 was substantially reduced only at potentials more negative than -2.4 V versus SCE, while in the presence of a cluster, the reduction took place at around -1.7 V thus, potential shift of ca. 0.7 V was achieved. The products were analyzed by means of gas chromatography and isotachophoresis. Without a catalyst, oxalate was the main product, and addition of small amounts of water to the DMF solution favored formate production, whereas in the presence of the catalyst, formate was produced predominantly even in a dry DMF solution. This result was interpreted in terms of indirect reduction of C02, proceeding by electron transfer from the reduced cluster to C02 in the bulk... 

Figure 3.48 Reflectance spectra collected off a Pt electrode immersed in CO2-saturated CHjCN/0.1 M tetrabutylammonium tetrafluoroborate. The reference spectrum was taken at the base potential of — 0.8 V vs. SCE. The potential was then stepped down to successively lower values, further spectra collected and normalised to the reference spectrum. The spectra were collected at — 1.0 V, — 1.2 V, —1.4 V. —1.6 V, — 1.8 V and - 1.9 V. The spectrum at - 1.0 V showed little or no features, bands then grew in intensity as the potential was stepped down.

The electrochemical generation of the germyl anion has been the subject of a recent paper105. Evidence for its formation by SET reduction of Ph3GeH on Pt in DMF with tetrabutylammonium tetrafluoroborate is based on 13C NMR which shows a strong down-field shift of Ca 30 ppm for the ipso carbon of the anion. The anion tends to yield Ph3GeGePh3 above 20 °C, but is also trapped by reactions at —40°C with O2 and CH3I ... 

There are a few reports of poly(naphthalene) thin films. Yoshino and co-workers. used electrochemical polymerization to obtain poly(2,6-naphthalene) film from a solution of naphthalene and nitrobenzene with a composite electrolyte of copper(II) chloride and lithium hexafluoroarsenate. Zotti and co-workers prepared poly( 1,4-naphthalene) film by anionic coupling of naphthalene on. platinum or glassy carbon electrodes with tetrabutylammonium tetrafluoroborate as an electrolyte in anhydrous acetonitrile and 1,2-dichloroethane. Recently, Hara and Toshima prepared a purple-colored poly( 1,4-naphthalene) film by electrochemical polymerization of naphthalene using a mixed electrolyte of aluminum chloride and cuprous chloride. Although the film was contaminated with the electrolyte, the polymer had very high thermal stability (decomposition temperature of 546°C). The only catalyst-free poly(naphthalene) which utilized a unique chemistry, Bergman s cycloaromatization, was obtained by Tour and co-workers recently (vide infra). 

The step 1 product (0.009 mmol) and tetrabutylammonium tetrafluoroborate (0.598 mmol) were dissolved in 0.1 ml of acetonitrile and the solution added to a test tube containing 4-chloropyridine (0.50 mmol). After the mixture was heated for 30 minutes at 60°C the conversion rate reached 80%. The reaction mixture was then cooled to ambient temperature and concentrated. A yellow brown residue was isolated and was washed with diethyl ether and then dried under vacuum at ambient temperature and the product isolated having an average degree of polymerization of 52. 

The same reaction was performed without using the accelerating agent tetrabutylammonium tetrafluoroborate by Schmidt (1). The yellow brown solids... 

Tetrabutylammonium tetrafluoroborate [429-42-5J M 329.3, m 161.8". Recryst from H2O, aqueous EtOH or from EtOAc by cooling in Dry ice. Acetate m 118 2° (from BuCl) bromide m 118° (from EtOAc) and nitrate m 120° (from CgHg). [JACS 69 2472 1947, 11 2024 7955]. 

In another example13 the oxidation of propene is carried out with an electrolyte consisting of dichloromcthane containing 0.2 M tetrabutylammonium tetrafluoroborate and 2 % acetic acid. The potential of the platinum anode is controlled at 3.05 V versus aqueous SCE. The two major products are 3-acetoxyprop-1-ene (20%) and l-acetoxy-2-fluoropropane (30%). 

Tetrabutylammonium tetrafluoroborate (TBATFB, Bu4NBF4) is another excellent electrolyte for general use. Like other tetrafluoroborate salts, it is somewhat more soluble in both organic compounds and water than TBAHFP, and is more stable than TBAHFP in methylene chloride. House and coworkers have described procedures for the synthesis of TBATFB and other tetraalkyl-ammonium tetrafluoroborates [9]. Thus, a solution of 8.4 g (0.025 mol) of... 

Half-wave potential (-E1/2) vs. saturated calomel electrode (SCE). Values vs. Ag AgCl or Fc /Fc have been converted to vs. SCE using a conversion factor of 0.045 V or 0.49, respectively [96]. bDMF = dimethylformamide, DMSO = dimethylsulfoxide, DCM = dichloromethane, DCB = dichlorobenzene, THF = tetrahydrofuran, TBAP = tetrabutyl ammonium perchlorate, TBABF4 = tetrabutylammonium tetrafluoroborate, t-butyl = tert-butyl... 

In an EC2j process, the initial ET step is followed by a second-order irreversible homogeneous reaction. For example, the feedback mode of SECM was employed to study the reductive hydrodimerization of the dimethyl fumarate (DF) radical anion [22]. The experiments were carried out in solutions containing either 5.15 or 11.5 mM DF and 0.1 M tetrabutylammonium tetrafluoroborate in A,A,-dimethyl form amide (DMF). The increase in the feedback current with increasing concentration of DF indicated that the homogeneous step involved in this process is not a first-order reaction. The analysis of the data based on the EC2 theory yielded the fc2 values of 180M-1 s-1 and 160M-1 s-1 for two different concentrations. Another second order reaction studied by the TG/SC mode was oxidative dimerization of 4-nitrophenolate (ArO-) in acetonitrile [23]. In this experiment, the tip was placed at a fixed distance from the substrate. The d value was determined from the positive feedback current of benzoquinone, which did not interfere with the reaction of interest. The dimerization rate constant of (1.2 0.3) x 108 M x s-1 was obtained for different concentrations of ArO-. 

Anodic oxidation of homo allyltrimethylsilylmethyl ethers 238 or homo allyl trimethyl-stannyl methyl ethers in the presence of tetrabutylammonium tetrafluoroborate results in the formation of fluorine- containing tetrahydropyrans 239249(equation 131). The process involves formation of a resonance stabilized carbocation and its intramolecular cycliza-tion by the participation of a neighboring vinyl group, followed by attack of fluoride ion. This process is a convenient way to form the C—F bond involving electrochemical steps. 

TBAP = tetrabutylammonium perchlorate DMF = dimethylformamide TBABF4 = tetrabutylammonium tetrafluoroborate ACN = acetonitrile... 

Dibenzyl ditellurium was obtained in 70% yield by alkylation of the electrochemically generated ditelluride dianion with benzyl chloride in acetonitrile3. The ultrasonically promoted electrochemical reduction of tellurium powder was performed in H-type cells with the compartments separated by glass frits. Acetonitrile served as solvent and tetrabutylammonium tetrafluoroborate or hexafluorophosphate as the supporting electrolyte. At potentials beyond -1.1 V the dark-red ditelluride dianion is formed in the cathode and in the central compartment3. 

Abbreviations DMF, dimethylformamide MeCN, acetonitrile THF, tetrahydrofuran DMSO, dimethylsulfoxide PC, polycarbonate TBAI, tetrabutyl-ammonium iodide TBAP, tetrabutylammonium phosphate TBABF4> tetrabutylammonium tetrafluoroborate TRAP, tetraethylammonium phosphate. Vsersus Ag Ag+ (0.01 M) in NH3 at -50°C. Versus Ag AgN03 (sat d) in SO2 at -40°C. 

Tetrahexylammonium perchlorate and tetrabutylammonium tetrafluoroborate have been used as supporting electrolyte in benzene and chlorobenzene, respectively. The latter was suggested [418] to be an excellent solvent for the study of reversible oxidations and reductions of aromatic compounds. The TLV for chlorobenzene is 75 ppm. 

The general electrochemical procedure for the carbon dioxide incorporation was based on the use of one-compartment cells fitted with consumable anodes of magnesium or zinc [12]. Electrocarboxylations were carried out in DMF at constant current density, using tetrabutylammonium tetrafluoroborate (10 2 m) as supporting electrolyte. The catalyst was introduced in a 10% molar ratio with respect to the substrate and carbon dioxide was bubbled through the solution at atmospheric pressure. Electrolyses were generally run at room temperature and reactions were stopped when starting material was consumed or when the faradaic yield attained 30%. 

Numerous studies have now focussed on this technique of using diazonium salts for modifying electrode surfaces for a whole host of applications[9,57,58,63-65]. For example, Hong and Porter[66] have reported the electrochemical reduction of benzenediazonium tetrafluoroborate in acetonitrile containing tetrabutylammonium tetrafluoroborate to... 

In this Chapter the following common abbreviations are used CV, cyclic voltammetry RDE, rotating disk electrode rds, rate-determining step TBABF4, tetrabutylammonium tetrafluoroborate TBAPF6, tetrabutylammonium hexafluorophosphate TEAP, tetraethylammonium perchlorate TBAP, tetrabutylammonium perchlorate DMSO, dimethyl... 

Fig. 10 Cyclic voltammetric (CV) reduction and oxidation scans of a terfluorene at 2.5 x 10 1 M in acetonitrile and toluene (1 1 v/v) with 0.1 M tetrabutylammonium tetrafluoroborate as the supporting electrolyte using a glassy carbon electrode...

Tetrabutylammonium tetrafluoroborate (BU4NBF4) is usually used as a supporting electrolyte, and dichloromethane (CH2CI2) is suitable as the solvent because of its low viscosity at low temperatures. Trifluorometha-nesulfonic acid (CF3SO3H or TfOH) is added in the cathodic chamber to facilitate the reduction of protons in the cathodic process. It should be noted that both an anodic process and a cathodic process take place simultaneously in electrochemical reactions, and both processes should proceed smoothly to promote the overall reaction. 

The organic salt of tetrabutylammonium tetrafluoroborate (BujNBF ) was further dissolved into the basic organic solution at an appropriate concentration. The thickness of the spin-coated organic layer was about 80 nm. Then, an A1 cathode layer (100 nm) was formed on the top of the organic layers via thermal deposition at a rate of 0.7 nm/ s under a base pressure of 2 x 1Q Torr. In this experiment, phosphorescent OLEDs were fabricated and comprared one with BU4NBF4 (0.0050 wt%) annealed electrically at V = +7 V (forward bias) at T = 65°C the other for reference with BU4NBF4 (0.0050 wt%) annealed electrically at V = +20 V (forward bias) at T = 25°C. It should be noted that, except for the emissive layer, the device structure of the reference device was identical to that of the sample device. The structures of the devices and materials used were identical. The devices were prepared in inert Ar gas environments this preparation included electrical and thermal treatments. 

The counterion employed also has a marked effect on the electropolymerization process in organic solvents. For example, the polymerization of poly(methyl carboxypyrrole) (PMCP) proceeds differently in para-tolucncsul Ionic acid (pTS), tetrabutylammonium perchlorate (TBAP), tetrabutylammonium tetrafluoroborate (TBABF4), and tetrabutylammonium hexafluorophosphate (TBAPF6).63 As reported in that work, the rate of polymerization (at constant potential) and the time required for the onset of polymer deposition varied with the counterion employed. 

FIG. 7 Cyclic voltammogram of a self-assembled spherical gold microelectrode, (a) In a 7.5 mM aqueous solution of hexaamineruthenium(III) chloride and 1 M KC1 electrolyte. Electrode diameters, from top to bottom, 10, 5, 4, 3, 1.7 /rm. Scan rate 0.1 V/s. (b) In a 6.5 mM solution of tetracyanoquinodimethane in acetonitrile. Supporting electrolyte tetrabutylammonium tetrafluoroborate (0.1 M). Electrode diameter 6 /am. Scan rate 0.1 V/s. (Reprinted with permission from Ref. 20. Copyright 1997 American Chemical Society.)... 

The exciplexes formed between arenes and good acceptors such as dicyanobenzene can dissociate to radical ion pairs if the solvent used is sufficiently polar. The radical cation of the arene is then susceptible to attack by nucleophiles and this can lead to products of addition or substitution of the arene. A preliminary account of how salts such as tetrabutylammonium tetrafluoroborate can serve to mediate the charge separation in less polar solvents was reported last year. A second paper from the same group has now been published which describes the formation of the amino substituted dihydrophenanthrene (86) during the irradiation of a solution of phenanthrene, dicyanobenzene and propylamine in relatively non-polar solvents such as THF in the presence of tetrabutylammonium tetrafluoroborate. In the absence of the salt no product is formed. 

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