Lithium naphthalide reduction

The first examples of mononuclear disulfur and diselenium complexes of platinum have been described.330 Reduction of the sterically hindered complex trans- PtC 2( P M e2A r)2] (Ar = 2,4, 6-tris[bis(trimethylsilyl)methyl]phenyl, 2,6-bis[bis(trimethylsilyl)-methyl]-4-[tris(trimethylsilyl) methyl]-phenyl) with lithium naphthalide in THF solution affords the platinum(0) species [Pt(PMe2Ar)2]. Oxidative addition of elemental sulfur or selenium yields the dichalcogenatoplatinum(II) complexes of the type [PtE2(PMe2Ar)2] (E = S, Se) containing a unique PtE2 ring system. The complexes are stable to air in the solid state, but slowly decompose in solution after several days at room temperature. 

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. 

The highly reactive cadmium can be prepared by two different methods. One approach is a room temperature reduction of CdC with lithium naphthalide in THF or DME. The second approach allows the preparation of the reactive metal in a hydrocarbon solvent. First, lithium naphthalide is prepared in benzene addition of this solution to CdC produces a highly reactive cadmium powder. 

The reduction of a solution of a trialkylphosphine copper(I) iodide complex (CuIPR ) with preformed lithium naphthalide (LiNp) in THF or DME under argon was found to give a more reactive copper species, which will undergo oxidative addition with a variety of organic substrates at room... 

The reduction of di(neopentyl)gallium chloride with lithium naphthalide was reported to afford the gallium clusters (Ga-CH2CMe3) , but their structures are hitherto unknown. It was assumed that different species with up to 12 gallium... 

In the reduction of conjugated dienes cis 1,4-addition of trimethyl-chlorosilane to give c -l,4-bis(trimethylsilyl)-2-butene is favored with sodium in THF, lithium naphthalide in THF, and with lithium in diethylether. It appears that the anion radical, which in nonionizing solvents should exist in a cis configuration, leads to the cis 1,4-addition of the silyl groups, whereas the dianions produced by further reduction lead to trans products (140). 

In the application of this methodology to the preparation of C-glycosides, Beau and Sinay [183] utilized dimethyl carbonate as an electrophile. As shown in Scheme 7.65, the resulting product mixture favored the (3 oriented ester group in a ratio of 20 1. Subsequent reductive cleavage of the phenylsulfone was accomplished on treatment with lithium naphthalide giving the a-C-glycoside in 72% overall yield. Similar results were observed when phenyl benzoate was used as an electrophile. 

Similar reductive lithiations are available from 2-deoxy sugars. As shown in Scheme 3.2.3, tri-O-benzyl glucal was converted to the desired 2-deoxy glucopyranosyl chloride on treatment with hydrochloric acid. Following formation of the chloride, Lancelin, etal.,14 effected formation of the a lithiated sugar, via initial conversion to the axially oriented anionic radical, on treatment with lithium naphthalide. 

The addition of lithium naphthalide to [V(r -arene)2] leads to the disappearance of the ESR spectrum typical of the neutral vanadium radical. The postulated (410, 411) one-electron reduction was confirmed by NMR spectroscopy which showed that the blue solution generated when [V(>/-CeH6)2] reacts with potassium in 1,2-dimethoxyethane contains [V( j-C6H6)2r (412). 

The reduction of [Cr(>f6-naphthalene)2]+ by lithium naphthalide was thought to give [Cr(>f6-naphthalene)2] (410), but this is doubtful since the formal potential of the naphthalene-naphthalide couple is at least several hundred millivolts positive of that of the complex (416). A similar reaction between [Cr(f/-C6H6)2]+ and alkali metals in thf or 1,2-dimethoxyethane yielded the radical [Cr(f/-C6H6)(f/-C6H5)] (36) ESR spectroscopy showed an intramolecular, interannular hydrogen exchange reaction (Scheme 32) with a rate of 107 sec"1 (430). 

Chloropyridine (68) was converted into lithiopyiidine via reductive lithiation using lithium naphthalide as an electron transfer agent (Scheme 34) (94H(37)1467>. 

Bis(lithiomethyl)diphenylsilane (5) is readily available by a reductive cleavage of the C-S bond of bis(phenylthiomethyl)diphenylsilane (4) with lithium naphthalide (Eq. 2) [16-18]. Addition of... 

Moreover, the copper metal obtained by reduction of CuCl, CuI(PEt3) or Cu(SMe2)Cl with the lithium naphthalide, known as Rieke copper, is able to couple a range of aryl halides to biaryls at room temperature in very high yields [27]. For example, simple halobenzenes react with Rieke copper at room temperature to form phenylcopper(I) reagents which, upon refluxing in DME at 80 °C for 24 h, gave 66% of biphenyl. The... 

CaflHjgCr Bis (naphthalene)chromium(-III) Nr. 33, tri-anion Reduction with lithium naphthalide/ THF EPR/ 293 1.990 H 0.49 70Hen2... 

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