Thallium Cyclopentadienide

The reaction is very dependent on the purity of the lithium dispersion surface. As the lithium dispersion (which is being stored in the dry box) ages, the lithium has to be activated by adding 50 mL of diethyl ether, and later the reaction has to be initiated by using a warm water bath. These steps cause a decrease in the yield of Li[CH2(SiMe3)] and complicate the sublimation of pure Li[CH2(SiMe3)] because larger amounts of the red by-products are obtained. 

Shriver, The Manipulation of Air-Sensitive Compounds, McGraw-Hill, New York, 1969. 

Submitted by A. J. NIELSON, C. E. F. RICKARD, and J. M. SMITH Checked by BRUCE N. DIELt 

Reagents used for introducing the cyclopentadienyl ligand (Cp) into metal complexes often give low yields of product or suffer from difficulties in handling. 

The frequently used and easily prepared NaCp in tetrahydrofuran solution is extremely sensitive to traces of oxygen and does not store well. Product yields are usually lower with CpMgBr or CpjMg/ both of which are air-sensitive, with the latter involving a tedious preparation. Dicyclopentadienylmercury has low thermal stability and does not store well. 

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The reaction of 1,2-dithiolanes with 2- and 4-picolyllithium has been examined <96PS(112)101> and the reactions of thioanhydrides such as 94 with both thiols <95JOC3964> and amines <96TL5337> have been reported. Treatment of 1,2-dithiolium salts with lithium or thallium cyclopentadienide results in formation of a variety of bi-, tri- and tetracyclic products <96LA109>. Reaction of 95 with trimethyl phosphite gives some of the desired coupling product but also the phosphonates 96 <96PS(109)557>. 

Sodium and thallium cyclopentadienide provide more versatile syntheses of ferrocene and other metallocenes. 

Thallium cyclopentadienide is often used when the reducing power of the sodium salt is too great. The limited solubility of the thallium complex in organic solvents and its toxicity are its chief disadvantages. 

In 1971, a preparation of 1 from 2 using thallium cyclopentadienide was reported (I) but the toxicity of thallium and the mass of the reagent needed render this procedure unsuitable for large-scale preparations. An improved method was reported by Bruce et al. (3,4), using cyclopentadiene, ruthenium trichloride hydrate (3), and triphenylphosphine, which gives the desired complex in high yield [Eq. (2)]. The primary advantage of this latter method is formation of the complex in one pot. 

Vanadocene halide is another important analog that is transformed to various vanadocene derivatives. Vanadocene chloride is prepared from vanadium(III) chloride and thallium cyclopentadienide or vanadocene and hydrogen chloride. Vanadocene dihalide is similarly synthesized from vana-dium(IV) halide via nucleophilic substitution. " Displacement of the chloro group results in functionalization as shown in Scheme 15. 

The complexes 3 and 5 were transformed into the mixed sandwich complexes 6 by reaction with thallium cyclopentadienide in benzene and with sodium cyclopentadienide in ethanol, respectively. The structure was determined by X-ray crystallography. ... 

The reaction of trisubstituted cyclopropenylium salts 1 with hexacarbonylmolybdenum(O) or tetracarbonylmolybdenum(O) complex afforded the complex salt 15 or 16. The same reaction with 17, followed by treatment with thallium cyclopentadienide, yielded complex 18. - The structures of 16 (X = Br) and 18 (R = Ph, t-Bu) were determined by X-ray crystallography. 

In a similar manner, the reaction of 1 -rcr/-butyl-2,3-diphenylcyclopropenylium hexafluorophosphate (19) with hexacarbonyltungsten(O), followed by treatment with thallium cyclopentadienide, gave the tungsten complex 20. ... 

Thallium cyclopentadienide is, however, more conveniently prepared by the reaction of thallium hydroxide with cyclopentadiene, a procedure which will be described under Method 2. 

The synthesis of ionic cyclopentadienides of thallium and potassium in aqueous solution is somewhat surprising in view of the much greater acidity of water compared to cyclopentadiene. The presence, however, of a small concentration of cyclopentadienide anions in basic aqueous solution has been detected by UV spectrophotometry (26). The extreme insolubility of thallium cyclopentadienide presumably is sufficient to permit its nearly quantitative precipitation from 1 M potassium hydroxide solution (27-29). Greater solubility and ease of hydrolysis of potassium cyclopentadienide requires the use of saturated potassium hydroxide for its preparation (30). Potassium cyclopentadienide prepared in this manner is a white, air-sensitive precipitate with a curdy appearance. 

Resolution of 42 was accomplished by traditional methods. Conversion of 42 to hydroxy acid 53 was followed by resolution as its ephedrine salt. Variants of the Diels-Alder reaction were developed. For example, use of thallium cyclopentadienide (rather than sodium cyclopentadienide) provided a more stable, less basic nucleophile for use in generation of 37. 

The rhodium (triphenylphosphine)(ethene) complex CpRh(PPh3)(C2H4) 349, was synthesized by the reaction of [RhCl(G2H4)2]2 with triphenylphosphine and thallium cyclopentadienide. As in CpRh(PMe3)(C2H4), the coordinated ethene ligand may be displaced photochemically, affording a series of oxidative addition reactions.Complexes of the type Cp Rh(olefin)2 are found to be excellent catalysts for the isomerization of aldehydes or transfer formylation reactions." Divinyl disiloxane or divinyl disilazane afforded the preparation of several complexes of Rh-Cp, such as 350, 351, and 352. ... 

Actinides. Monocyclopentadienyl derivatives are less common and the majority of the reported complexes are Lewis-base adducts of the type CpAnXs-Ln (X = halide). Their steric and electronic unsaturation make their synthesis challenging. The first CpUCl3 2L compounds in ethereal solvents (DME or THF) were prepared by reacting UCI4 with thallium cyclopentadienide (Marks and Ernst 1982). 

Treatment of the sulphonium chloride (15) with thallium cyclopentadienide gives the bis(dimethylsulphonio)cyclopentadienide (16), isolated as the perchlorate the tri-substituted salt (17) has also been obtained/ ... 

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