Tetraethylammonium salts

In a similar manner, the diffusion of hexane into dichloromethane solutions containing mixtures of the alkylammonium salts of bromide and the olefinic acceptors o-CA and TCNE result in the formation of brown-red crystals [23]. X-ray analysis reveals the (1 1) complex of bromide with o-CA, in which the anion is located over the center of the C - C bond of the acceptor moiety (Fig. 15b) and Br - C contacts are shortened by as much as 0.6 A relative to the sum of van der Waals radii (Table 3). In bromide complexes with TCNE, the location of the anion relative to the acceptor is variable. In fact, a 2 1 complex [(Br )2,TCNE] is isolated in which both anions reside over the olefinic bond when the tetraethylammonium salt of bromide is used. In comparison, if the tetrapropyl- or tetrabutylammonium salts of the same anion are employed, the (1 1) complexes [Br ,TCNE] are formed in which the bromide donors are shifted toward the cyano substituents (Fig. 15a). In both cases however, the short intermolecular separations that are characteris-... 

Recently, Mascal and Ceron Bertran <2005JA1352> reported the preparation and characterization of 35 (aza-analogue anions of triquinacenes) which are stable enough in THF solution (in the absence of acid). Moreover, the hexachloro anion 35b could be isolated as tetraethylammonium salt by column chromatography on alumina. As expected, anion 35a was more nucleophilic than 35b. Indeed, only the former could be benzylated leading to 36a. However, 35b reacts easily with molecular bromine at low temperature yielding the corresponding a,a,a-tribromide 37b or dibrominated ether 37 b when this bromination was conducted in THF. 

Much emphasis has been placed on the selectivity of quaternary ammonium borohydrides in their reduction of aldehydes and ketones [18-20]. Predictably, steric factors are important, as are mesomeric electronic effects in the case of 4-substituted benzaldehydes. However, comparison of the relative merits of the use of tetraethyl-ammonium, or tetra-n-butylammonium borohydride in dichloromethane, and of sodium borohydride in isopropanol, has shown that, in the competitive reduction of benzaldehyde and acetophenone, each system preferentially reduces the aldehyde and that the ratio of benzyl alcohol to 1-phenylethanol is invariably ca. 4 1 [18-20], Thus, the only advantage in the use of the ammonium salts would appear to facilitate the use of non-hydroxylic solvents. In all reductions, the use of the more lipophilic tetra-n-butylammonium salt is to be preferred and the only advantage in using the tetraethylammonium salt is its ready removal from the reaction mixture by dissolution in water. 

The potassium channel, on the other hand, is blocked by both tetraethylammonium salts (7.3, TEA) and nonyl-triethylammonium (7.4) salts, indicating the presence of a hydrophobic binding site that accommodates the nonyl group. Both blocking agents must be applied intra-axonally, which is understandable if one considers that the K current is always directed outward. 

The observation of a bent Cr-H-Cr bond in the tetraethylammonium salt without an accompanying substantial deformation of the linear architecture of the nonhydrogen atoms in the [Cr2(CO)io(M2-H)] monoanion reflects the inherent flexibility of the bond. The deformability of the[M2(CO)io(M2-H)] monoanion species to adopt an appreciably bent, staggered carbonyl structure was first reported by Bau and co-workers (23) from neutron diffraction studies of two crystalline modifications of the electronically equivalent, neutral W2(CO)9(NO)(m2-H) molecule. Subsequent x-ray diffraction studies (15) of the analogous [W2(CO)io(m2-H)] monoanion found that the nonhydrogen backbone can have either an appreciably bent structure for the bis(triphenylphosphine)-iminium salt or a linear structure for the tetraethylammonium salt, with the W-W separation 0.11 A less in the bent form. Crystal packing forces probably were responsible (15) for the different molecular configurations of the monoanion in the two lattices. In solution, however, all known salts of the [W2(CO)io(m2-H)] monoanion exhibit the same three-band carbonyl ir absorption spectrum char-... 

The ternary hydride was purified by reprecipitation from aqueous methanolic sodium hydroxide. Na2ReH9 was soluble in water and methanol, slightly soluble in ethanol, and insoluble in 2-propanol, acetonitrile, ether, and THF. Decomposition started at approximately 245°C when heated in a vacuum, with the evolution of hydrogen and sodium as the temperature increased. Na2ReH9 was a precursor for the preparation of the tetraethylammonium salt, the potassium salt, and the mixed potassium sodium salt of nonahydridorhenate(VII). 

Figure 4 The structure of the tris(ethylxanthato)tellurium(II) anion in its tetraethylammonium salt (reproduced by...

All attempts to protonate the partially exposed carbon atom in 1 have been unsuccessful (1,5). Reaction with base yields [Fe5C(CO)14]2- (2), which was isolated as its tetraethylammonium salt (5). The dianion may also be synthesized by the reaction of Fe5C(CO)15 and [Fe(CO)4]2-, and although its structure is as yet undetermined, it presumably retains a square pyramidal core (4). 

Depression of autonomic ganglionic transmission—certain quaternary ammonium compounds, such as tetraethylammonium salts. 

In both polarographic and preparative electrochemistry in aptotic solvents the custom is to use tetraalkylammonium salts as supporting electrolytes. In such solvent-supporting electrolyte systems electrochemical reductions at a mercury cathode can be performed at —2.5 to —2.9 V versus SCE. The reduction potential ultimately is limited by the reduction of the quaternary ammonium cation to form an amalgam, (/ 4N )Hg , n = 12-13. The tetra-n-butyl salts are more difficult to reduce than are the tetraethylammonium salts and are preferred when the maximum cathodic range is needed. On the anodic side the oxidation of mercury occurs at about +0.4 V versus SCE in a supporting electrolyte that does not complex or form a precipitate with the Hg(I) or Hg(II) ions that are formed. 

The tellurium atom in the tetraethylammonium salt is surrounded by five sulfur atoms situated at the corners of a pentagon. The almost planar TeS5 group is formed by one monodentate and two bidentate dithiocarbonato ligands3. 

One of the chlorides in this complex can be exchanged for perchlorate on treatment of a solution of the complex in dichloromethane/acetonitrile with silver perchlorate2. Dicarbonyl(chloromethylidyne)[hydrotris(pyrazol-l-yl)borato]molybdenum(IV) reacted with sodium telluride in aqueous methanol to produce the anionic dicarhonyl[hydro-tris(pyrazol-l-yl)borato telluracarbonylmolybdate(0), which was isolated as the moderately air-stable tetraethylammonium salt. This salt reacted with methyl iodide in acetonitrile to form dicarbonyl[hydrotris(pyrazolo)borato](methyltelluromethylidyne) molybdenum(IV)3. 

The compound K2 [Rh6(CO)15C] is a yellow powder. It is sensitive to air both in the solid state and in solution and is quite soluble in water, methanol, ethanol, acetone, THF, and acetonitrile. The salts of other cations can be obtained by metathesis, in water for the cesium salt and in methanol for the larger tetra-alkylammonium or phosphonium cations. The tetraethylammonium salt is sparingly soluble in THF, whereas the benzyltrimethylammonium and bis-(triphenylphosphine)imminium salts are soluble. All of these salts are soluble in acetone and acetonitrile. The yellow solution of the potassium salt in THF shows characteristic IR bands at 2040 (vw), 1990 (vs), 1885 (vw), 1845 (s), 1830 (sh, m) 1815 (sh, br) and 1775 (vw, br) cm-1. The IR spectral band shapes depend on solvents and cations. The oxidation of K2 [Rh6(CO)i5C] with iron-(III) ammonium sulfate in water under carbon monoxide leads to the octa-nuclear carbido carbonyl cluster Rhg(CO)i9C,6 whereas under nitrogen RhntCO sQ7 or [H30] [Rhls(CO)28C2]8 is obtained. 

Double exchange with the bulky ammonium cations is simply carried out in alcoholic solution. The tetramethyl- and tetraethylammonium salts are insoluble in THF, while salts of larger cations, such as tetrabutyl- and benzyl-trimethylammonium and /J-nitrido-bis(triphenylphosphorus)(l+), are soluble. All these salts are soluble in acetone and acetonitrile. 

The dianion [Fe3(CO)n]2 was first isolated by Hieber1 as the [Fe(en)3]2 + (en = ethylenediamine) salt. Attempts to prepare the tetraethylammonium salt were unsuccessful.2 In the synthesis reported here, this dianion is isolated as the /j-nitrido-bis(triphenylphosphorus)(1+) salt, (Ph3P)2N+, which affords high yields of a pure product. 

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