Complexes alkali metal naphthalenide

Scheme 9.13 Ring-opening mechanism of P-butyrolactone using complexed alkali metal naphthalenide [44],...

Anionic Alkoxides RO" M (M=alkali metal, complexed or not by crown ether) Carboxylates RCOO" (M=alkali metal) Alkali metal naphthalenides Alkali metal supramolecular complexes Grafitides KC24... 

Treatment of MX5 with alkali metal naphthalenide in DME at —60 °C provides thermally unstable brown intermediates, assumed to be [M(C10H8)2] or [M(l-MeCioH7)2], which react with CO (1 atm) to give [M(CO)6]- in 30-54% yields.718 Carbonylation, using sodium in the presence of cyclooctatetraene in THF under CO (1 atm, 40 °C), has also been reported, although its efficiency is low in the case of Ta (12%).719 Cyclooctatetraene complexes are thought to form as intermediates, but the mild carbonylation conditions compared to those of [Nb(COT)3]- (50 atm, 100 °C) suggest that a compound of different stoichiometry may be involved.720... 

The complex is stable in air for a short time, but is sensitive to hydrolysis it melts at 171 °C without decomposition. From equations 64 and 65 it can be assumed that 82 is reduced by alkali metal naphthalenides, but not by potassium anthracenide, and this assumption was proved in separate experiments182. 

The reductive alkylation of coal, involving reduction by alkali metal naphthalenide followed by alkylation by alkyl halide, involves chemistry that is more complex than that of the reductive alkylation of simple aromatic compounds. 

Neutral Ti(CO)6 is an extremely unstable compound which decomposed even below -220 °C, as shown by matrix isolation spectroscopy [165]. The much more stable phosphine derivatives Ti(CO)3(dmpe)2, Ti(CO)5(dmpe), Ti(CO)5(PMe3)2, Ti(CO)4(PMe3)3 have been isolated [166-168]. In contrast, the dianionic salt [Ti(CO)6] (53) is thermally much more stable and decomposes only above 200 C. Complex 53 was obtained by reductive carbonylation of Ti(CO)3(dmpe)2 by alkali metal naphthalenides in the presence of cryptand [169]. Carbonylation of 79 also produces 53 [170]. The naph-thalenide-assisted reductive carbonylation of the zirconium tetrachloride afforded the zirconium analog [Zr(CO)6] (54) [171], which was also derived by carbonylation of the tris(diene) dianion 45 [150]. One anion [R3Sn] effectively stabilizes Ti(CO)e as an air stable monoanionic salt, [R3SnTi(CO)J [172]. 

Naphthalene complexes CioH8Ln(THE) (Ln - Eu, Yb x - 2,3), obtained by reaction of Lnl2 with alkali metals naphthalenides, like the products of ytterbium and alkynes cocondensation, readily react with cyclopentadiene at room temperature to give Cp2Ln in a high yield [50]. 

The radical nature of the anion radical (X) has been established from electron spin resonance spectroscopy and the carbanion nature by its reaction with carbon dioxide to form the carboxylic acid derivative. The equilibrium in Eq. (8.13) depends on the electron affinity of the aromatic hydrocarbon and the donor properties of the solvent. Tetrahydrofuran (THF) is a useful solvent for such reactions. This fairly polar solvent (dielectric constant = 7.6 at room temperature) promotes transfer of the s electron from the alkali metal to the aromatic compound and stabilization of the resultant complex, primarily via solvation of the cation. Sodium naphthalenide is... 

From the experimental point of view, reductive desulfonylations with alkali metal arene radical anion complexes require a large excess of the radical anion, very short reaction times at low temperatures, and must be run under an inert atmosphere. Sodium or lithium naphthalenides in tetrahydrofuran at —78° or lower temperatures are typical reaction conditions. Tetrahydrofuran solutions of lithium naphthalenide are dark green. This color is lost when the substrate is added and restored once the reaction is finished. Upon completion, the excess reagent is quenched with a saturated aqueous solution of ammonium chloride or low molecular alcohols such as methanol or ethanol. 

The reduction is complete when the solution is clear and colorless. There should be no hint of the green naphthalenide radical anion visible in the supernatant solution. This slurry does not flash or show other indications of alkali metal when syringed onto the surface of water. If the reduction is incomplete or after a partial reaction of the activated copper, the aforementioned aqueous quench will cause the precipitation of white cuprous iodide (decomposition of the soluble copper complexes occurs). 

Significantly fewer unsupported and structurally characterized alkali metal-TM complexes are known, though they show similar motifs compared with their main group counterparts. For example, the cuprate complex [(THF)2Na-Cu(SFBu3)2j, 7, exhibits an almost linear Si—Cu—Si fragment (175.26(5)°) and a Na-Cu bond of 2.7393(18) A [68]. The rare 2,2 -biphosphinine-coordinated Ru complex 8 has been obtained from reduction of the corresponding Ru" chloride complex with sodium naphthalenide in DME. This has a Ru-Na bond of 3.072(2) A in the solid state [69] and is effective in salt metathesis reactions with Mel or RjSnCl (R = Me, Ph) to give substituted Ru" complexes. 

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