Naphthalide salts

Reduction can be effected by doping with alkali metals, either in the vapour phase or in solution, e.g. with naphthalide salts in THE Electrochemical doping is very well possible, for instance with LiB(Me)4 or NaB(Ph)4 in solution with a polyacetylene cathode. The representation (CH)M is often used to denote a certain composition. 

In solution, the reduction of fullerenes is typically performed in etheral solvents (e.g., tetrahydrofuran, dimethoxyethane) [138] or liquid ammonia [139]. Using Li as a reducing agent it is possible to reach the highest reduction step, the hexa-anion. With the other alkali metals this was observed only when naphthalide salt was added [140]. The reduction of C o and all the higher fullerenes to their hexa-anions was first made possible by sonication with excess Li [16] and later by adding a small amount of 2 as an electron shuttle (vide supra). 

A third approach is to use a stoichiometric amount of preformed lithium naphthalide. This approach allows for very rapid generation of the metal powders as reductions are diffusion controlled. Very low to ambient temperatures can be used for the reduction. In some cases the reductions are slower at low temperatures due to low solubility of the metal salts. 

This approach frequently leads to the most active metals as the relatively short reduction times at low temperatures leads to reduced sintering of the metal particles and hence higher reactivity. Fujita, et aL(62) have recently shown that lithium naphthalide in tqluepe can be prepared by sonicating lithium, naphthalene, and N, N, N, N-tetramethylethylene-diamine (TMEDA) in toluene. This allows reductions of metal salts in hydrocarbon solvents. This proved to be especially beneficial with cadmium(49). An extension of this approach is to use the solid dilithium salt of the dianion of naphthalene. Use of this reducing agent in a hydrocarbon solvent is essential in the preparation of highly reactive uranium(54). This will be discussed in detail below. 

However, when the reductions were carried out with lithium and a catalytic amount of naphthalene as an electron carrier, far different results were obtained(36-39, 43-48). Using this approach a highly reactive form of finely divided nickel resulted. It should be pointed out that with the electron carrier approach the reductions can be conveniently monitored, for when the reductions are complete the solutions turn green from the buildup of lithium naphthalide. It was determined that 2.2 to 2.3 equivalents of lithium were required to reach complete reduction of Ni(+2) salts. It is also significant to point out that ESCA studies on the nickel powders produced from reductions using 2.0 equivalents of potassium showed considerable amounts of Ni(+2) on the metal surface. In contrast, little Ni(+2) was observed on the surface of the nickel powders generated by reductions using 2.3 equivalents of lithium. While it is only speculation, our interpretation of these results is that the absorption of the Ni(+2) ions on the nickel surface in effect raised the work function of the nickel and rendered it ineffective towards oxidative addition reactions. An alternative explanation is that the Ni(+2) ions were simply adsorbed on the active sites of the nickel surface. 

Crystallisable salts and related compounds. Almost all crystallisable catalysts, such as sodium and lithium aromatic compounds (e.g. sodium naphthalide), -oyl salts such as aroyl hexafluorophosphates, alkoxides, and many others can be prepared in a vacuum system and then purified by repeated crystallisations and washings in a closed system (see Chapter 5) thereafter they can be distributed into breakable phials or other devices as described in Chapter 3. 

The reaction is spontaneous if a reverse potential is applied or the cell is short circuited. Low alkali metal concentrations are obtained by using solutions of salts such as sodium or potassium naphthalide in THF or n-butyllithium in hexane ... 

Lithium (8.46 mmol) and naphthalene (10.1 mmol) were mixed with 15 ml THF, stirred 2 hours, and then cooled to — 100°C. In a separate reaction vessel, CuCN (8.0 mmol) and LiBr (17.27 mmol) in 5 ml THF were stirred until the Cu(I) salt dissolved. The solution was cooled to —40°C and transferred into lithium naphthalide using a cannula and the mixture stirred 5 minutes. The catalytic agent was ready for immediate use. 

For this latter reaction, it should be noted that the use of potassium naphthalide leads to further reduction to K2[W(CO)5j thus, the milder reductant Na[Ph2CO] selectively leads to a less reduced complex [61]. M[Ph2CO] salts have instead been used in catalytic amounts as mediators (see Section 4.4). They are prepared by reduction of benzophenone in THF, DME, or ammonia by pieces of alkali metals (Li, Na, K) [68] ... 

The zinc metal is typically activated before use and methods for accomplishing this have been reviewed. The use of highly reactive forms of zinc (Reike powders), obtained by reduction of zinc salts with an alkali metal, detracts from the convenience of the classical procedure but much higher yields have been obtained, at least with the simple substrates that have so far been examined. One of the most convenient preparations of a Reike powder uses sodium naphthalide, as shown in Scheme 4. Reactive zinc powders so allow the use of a-chloro esters which are unsatisfactory with the usual forms of... 

Lithium naphthalide and uranocene in thf give the monoanion [U(r/-cot)2], isolated as a solvated lithium salt (405) neutral (406) and anionic (407) neptunium and plutonium analogs have also been prepared. 

The complex [Mn(fj-C5Me5)2] is oxidized to the monocation (E° = -0.56 V) and reduced to [Mnfo-C5Me5)2] (E° = -2.50 V in MeCN), which is isolable as a pyrophoric sodium salt using sodium naphthalide in thf. The anion is isoelectronic with ferrocene but does not add electrophiles to the rings and is stable to ring exchange. Needless to say, it is an extremely powerful one-electron reductant (442). 

A new type of diphosphane derivative (5) has been obtained recently during the reduction of the borane adduct (MeO)3P,BH3 with sodium naphthalide in 1,2-dimethoxyethane/ ° The product isolated as the sodium salt is thermally and hydrolytically stable, and, although the n.m.r. data are not wholly definitive, the trigonal-bipyramidal structure with an axial P—P bond (5) has been suggested. 

The synthesis of catenated polystyrene-cat-polyvinylpyridine with a molar mass of lODOOgmol was also reported. Polyvinylpyridine was synthesized by the lithium naphthalide-initiated sequential polymerization of 2-vinylpyridine. The catenane copolymer was obtained by end-to-end coupling of the P2VP dianion lithium salt with l,4-bis(bromomethylbenzene) in THF in the presence of a PS maaocyde (Mp = 4500gmoU ). The catenane was isolated by predpitation-extraction procedmes. 

The dissociation of growing macroions is greatly reduced by the addition of foreign salts (for example, Kalignost in the polymerization of styrene in tetrahydrofuran started by sodium naphthalide) ... 

Abiotic nonthermal methods include chemical processes such as reaction with molten sodium, sodium naphthalide, sodium salt in amine, catalytic dechlorination, wet air oxidation, ozonation, and physical methods including adsorption, microwave plasma, and photolysis. 

Naphtalides, alkalides, and alkali metals are sufficiently powerful to reduce Ge and Si salts to the elements. Si nanocrystals have been prepared in solution by the reduction of the halides with Na, Li naphthalide, and hydride reagents [216-219]. Similarly, Ge nanocrystals have been made by the reduction of GeCL with Li naphthalide in THF [217]. TEOS (Si(OEt)4) is readily reduced by sodium to yield Si nanocrystals. Si and Ge nanocrystals are frequently covered by an oxide layer. Y2O3 nanocrystals have been made by the alkalide reduction of YCI3 followed by oxidation by exposure to ambient conditions [220]. Yittria nanocrystals could be doped with Eu to render them phosphorescent [221]. ZnO nanoparticles have been prepared from zinc acetate in 2-propanol by the reaction with water [222]. Pure anatase nanocrystals are obtained by the hydrolysis of TiCL with ethanol at 0°C followed by calcination at 87° C for 3 days [223]. The growth kinetics and the surface hydration chemistry in this reaction have been investigated. 

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