Sodium and Potassium Cyclopentadienide

MICHAEL T. GAMER, and PETER W. ROESKY Checked by HYOJONG YOO and DONALD H. BERRY+ 

Alkali metal cyclopentadienide salts are important reagents in organometallic chemistry, having been used to prepare innumerable cyclopentadienyl complexes. Potassium cyclopentadienide, KCp, is usually made by deprotonation of cyclo-pentadiene with potassium metal either in organic solvents such as THF and benzene or in liquid ammonia, or by deprotonation with KH or KOH. The analogous sodium compound, NaCp, was reported by the groups of Fischer and 

Institut fiir Chemie und Biochemie, Freie Universitat Berlin, FabeckstraBe 34—36, 14195 Berlin, Germany Institut fiir Anorganische Chemie, Karlsmher Institut fiir Technologie (KIT), Engesserstr. 15, Geb. 30.45, 76131 Karlsmhe, Germany. 

Inorganic Syntheses, Volume 36, First Edition. Edited by Gregory S. Girolami and Alfred P. Satlelberger. 

Ziegler, and NaCp can be obtained by a similar deprotonation of cyelopentadiene with sodium metal, NaH, NaO-t-Bu, or NaOH. The disadvantage of all the reactions described above is that monomeric cyelopentadiene must be used as the starting material. Because monomeric cyelopentadiene is not stable at room temperature, it is usually freshly prepared by a thermal retro-Diels-Alder reaction from the commercially available dicyclopentadiene. 

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Metallic ytterbium is also utilized as a reducer for Cp2YbCl [17]. The yield of dicyclopentadienides in these reactions is 30-40%. The reactions of anhydrous halides LnX2 with sodium and potassium cyclopentadienides may be applied [3, 14, 23, 27, 52] to synthesize REM dicyclopentadienides. 

While this is the simplest method for preparing metal cyclopentadienyl compounds, it is one of the least general. It is limited to the elements Li, Na, K, Ca, and Sr and under rather vigorous conditions of temperature to Mg, In, Tl, and Fe. The reaction is usually carried out in the liquid phase at 25° to 100° C in the presence of a solvent for lithium, sodium, and potassium, or in the vapor phase at 400°- 600°C for the less reactive elements. Usually the cyclopentadienides of lithium, sodium, and potassium are not isolated but are used in solution as intermediates for the preparation of other cyclopentadienyl metal compounds. Compounds produced by reaction of cyclopentadiene vapor with metal are usually sufficiently volatile to sublime away from the reaction zone and condense in the cooler portion of the apparatus. 

Direct reaction between sodium or potassium and alkyl and aryl halides is complicated by exchange and coupling reactions, which can lead to mixtures of products. These complications can be reduced by rapid stirring and the use of finely divided metal or amalgams. Phenylsodium can be made in this way PhCl -h Na->PhNa-h NaCl. Acidic hydrocarbons react with alkali metals in ether solvents. Cyclopentadiene, for example, affords sodium cyclopentadienide in tetrahydrofuran (p. 279). Triphenylmethylpotassium is obtained as a deep red solution from triphenylmethane and potassium in 1,2-dimethoxyethane. These carbanions, in which the negative charge is delocalized over several carbon atoms, do not attack ethers, in contrast to the simple alkyl or aryl carbanions present in methylsodium or phenylpotassium. 

Cyclopentadienyl organometallic compounds can be prepared by a variety of reactions [49, 50]. The general method for actinides in the in and iv oxidation states is by reaction of potassium or sodium cyclopentadienide with the anhydrous actinide halide (AnX ) in an organic solvent such as tetrahydrofuran (THF), benzene, or diethyl ether. 

The reactions between [Os(=N)Ph2(py)2][BF4] and sodium cyclopentadienide or potassium indenide result in the formation of the half-sandwich nitrido-Os(vi) complexes [Os(=N)GpPh2] and [Os(=N)( 7 -G9H7)Ph2], respectively/ ... 

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