Alkali metal cyclopentadienyls

The (-l-)-neomenthylcyclopentadienyllanthanide complexes Cp LnX2(THF)3 [X = Cl, Ln = Sm, Gd, Yb, Y, Lu X = I, Ln = Sm, Yb Cp = (-l-)-neomenthylcyclopenta-dienyl] were prepared by reaction of LnCls with appropriate alkali metal cyclopentadienyl derivatives. In the solid state, the monomeric Cp Sml2(THF)3 adopts a pseudo-octahedral geometry with the two iodine atoms taking trans positions. A similar structure is found for (Ind)GdCl2(THF)3. 

The neutral complex Co (05115)2 has been obtained by the action of alkali metal cyclopentadienyls on the complex [CofNHs) ] (SCN)2 in liquid ammonia (69) and, more recently, by lithium aluminum hydride reduction of the [Co(C6H6)2]+ ion ( 9). It forms deep violet-black needles, melts at 173-174°, and is exceptionally sensitive to atmospheric oxidation. In organic solvents such as benzene, petroleum ether, ether, or... 

Neptunocene (NpCp4) can be prepared from NpCI and an alkali metal cyclopentadienyl organometallic compound (e.g., NaCp) in ether solvent (commonly THF) with cooling ... 

The formation of anionic rare earth metal ligand moieties or ate complexation are commonly observed features of salt metathesis reactions when alkali metal cyclopentadienyl [147], alkyl [96], amide [97,255] and alkoxide derivatives are employed [Eqs. (39)-(42)] [256]. 

Alkali metal cyclopentadienyl alanates may also be obtained (285) ... 

CpLi exists in ethers as a contact ion pair, in which the lithium ion is located above the cyclopentadienyl ring. The crystal structure of CpLi(12-crown-4) reveals analogous structural features. This complex has a sandwich-type structure in which the lithium ion is coordinated to the four oxygen atoms of the crown ether on one side and to the Cp ring on the other. Several X-ray structures of alkali metal cyclopentadienyl compounds containing silyl substitution of the Cp ligand have been reported. The structures of fluorenyl alkali metal complexes (Li-Cs) stabilized by diglyme have also been reported. The crown-ether-stabilized compounds of cyclopentadienyl, indenyl, and fluorenyl with the heavier metals, Rb and Cs, have also been reported. " A common structural feature is the rf coordination of... 

Thiele, J. Ber. Dtsch. Chem. Ges. 1900, 33, 666. In a recent review on alkali-metal cyclopentadienyl chemistry this paper is erroneously interpreted as reporting the preparation of sodium cyclopentadienide see Harder, S. Coord. Chem. Rev. 1998, 176,... 

Related chain polymers have also been found in several Lewis-base adducts of alkali metal cyclopentadienyl, indenyl, and fluorenyl complexes. Such adducts with ethers or amines have been thoroughly investigated because they form stable, crys-... 

The electrochemistry of the complexes [(RCsH4)-Mo(X)( i-X)2]2. X = multiply bonding ligand, has been studied. The bis[(tricarbonyl metal)(q -cycl(q)entadienyl)]methane derivatives, metal = Mo, W have been synthesised ftom the reaction of bis-(cyclopentadienyl)-methane with (CH3CN)3M(CO)3, followed by oxidation of the intermediate anions. The preparations of [(Cp )(q -allyl)(q -allyl)W], Cp = Cp, Cp, q-C5H4t-Bu, obtained from [(q -C3H5>3WCl]2 and alkali metal cyclopentadienyls have been described. ... 

Cyclopentadienyl and related derivatives. Alkali-metal cyclopentadienyl compounds have been featured in a highlight article in Angew.Chem. NMR spectra and oxidation potentials have been reported for Bu -substituted cyclopentadienyl-metal species. A crystal structure determination of [Ph4P][Cp2Li], obtained from Ph4PCl and CpLi in THF, revealed that the anions... 

Because of the large difference in electronegativity, the bonding in C5H5CS should have the most pronounced ionic character of all the metal cyclopentadienyls. Therefore, the purest spectrum of the anion should be obtainable with this compound. However, the sensitivity of the alkali metal cyclopentadienyls towards oxidation rises and the solubility in suitable solvents falls with increasing atomic weight of the metal. Because of these properties, more satisfactory results are obtainable with C5H5K. These results are listed in Table IX. 

The dimers [CpY(p.-0 Bu)(0 Bu)]2 and Cp2Y(p,-0 Bu)2Y(0 Bu)Cp have been synthesized in the context of reactivity studies of the trimetallic yttrium alkoxides Y3(0 Bu)7Cl2-(THF)2 with alkali metal cyclopentadienyl reagents (Evans et al. 1993a) and their X-ray structure determined. 

Reaction of the same neutral borabenzene-ligand adduct, C5H5B-PMe3, with a transition, rather than an alkali, metal alkyl or amide can furnish r 6-boratabenzene complexes in a single step (Scheme 8).17 This efficient transformation presumably proceeds through initial ir-coordination of CsHsB-PMes to the transition metal, followedby an intramolecular substitution reaction. In contrast to other approaches to the synthesis of T 6-boratabenzene complexes, this synthetic route does not have a parallel in if-cyclopentadienyl chemistry. 

Several tri(cyclopentadienyl)tin(ll) and lead(ll) complexes have been prepared with alkali metal cations. The arrangement of Cp rings around the metal is in a paddle wheel configuration the alkali cation is bound to Cp and not Sn or Pb, further supporting the view of a weak alkali metal group 14 bond. Representative examples of these compounds include (77S-Cp)2E(/r-Cp)-Na(PMDTA) (E = Sn 230, Pb 231).239 240... 

Bis[(tris(isopropyl)cyclopentadienyl)]zinc (Zn C5(Pr1)3H2 2, 21) and bis[(tetrakis(isopropyl)cyclopentadienyl)]zinc (Zn C5(Pr1)4H 2, 22) were synthesized from the respective potassium cyclopentadienides and zinc iodide as shown in Scheme 18.50 The same slipped sandwich compounds were also isolated from zinc-reduced VC13 solutions when they were treated with these alkali metal cyclopentadienides at room temperature.51 The outcomes of these reactions suggest that zincocenes are likely intermediates in the syntheses of transition metal metallocenes, in which the metal halides have been pre-reduced with zinc. The solid-state structure of Zn G5(Pr1)4H 2 is shown in Figure 10. The sole... 

The broader subject of the interaction of stable carbenes with main-group compounds has recently been reviewed. Accordingly, the following discussion focuses on metallic elements of the s and p blocks. Dimeric NHC-alkali adducts have been characterized for lithium, sodium, and potassium. For imidazolin-2-ylidenes, alkoxy-bridged lithium dimer 20 and a lithium-cyclopentadienyl derivative 21 have been reported. For tetrahydropyrimid-2-ylidenes, amido-bridged dimers 22 have been characterized for lithium, sodium, and potassium. Since one of the synthetic approaches to stable NHCs involves the deprotonation of imidazolium cations with alkali metal bases, the interactions of alkali metal cations with NHCs are considered to be important for understanding the solution behavior of NHCs. 

Of course, it is not without precedence as there are already various reviews and textbooks in the area. Most closely related to this work are the reviews by Setzer and Schleyer and by Weiss °. A textbook edited by Sapse and Schleyer contains chapters on various topics of lithium chemistry. Three reviews by StaUce, Harder and by Jutzi and Burford concentrate on cyclopentadienyl organometallic derivatives, containing also the s-block derivatives. Two reviews deal with the heavier alkali metal organics, the first written by Schade and Schleyer , the second by Smith . There are several chapters on lithium organics within more general metal organic publications ... 

Organosilyl substituted 7)5-cyclopentadienyl complexes may be prepared by two main procedures (a) reactions of silylated cyclopenta-dienes or their alkali metal derivatives, with an appropriate transition metal compound (carbonyl or halide) with formation of ir-bonds (b) metalation of a preformed 7j5-cyclopentadienyl complex, followed by treatment with an organohalosilane. 

Highlights in the chemistry of cyclopentadienyl compounds have been reviewed.65 Trends in the metallation energies of the gas-phase cyclopentadienyl and methyl compounds of the alkali metals have been studied by ab initio pseudopotential calculations. Whereas there is a smooth increase in polarity of M-(C5H5) bonds from Li to Cs, lithium appears to be less electronegative than sodium in methyl derivatives. The difference between C5H5 and CH3 derivatives is attributed to differences in covalent contributions to the M-C bonds. In solution or in the solid state these trends may be masked by the effects of solvation or crystal packing.66 The interaction between the alkali metal ions Li+-K+ and benzene has also been discussed.67... 

Two cyclopentadienyl units are bridged in 1,2 position by two dimethylsilyl groups in the ligand system 53. The isomeric mixture of 4,4,8,8-tetramethyltetrahydro-4,8-disila-.y-indacene139-144 is the starting material for metal complexes of a different kind. Deprotonation of this compound and metallation with alkali metal compounds have been investigated in detail142 143 (equation 60). 

The same synthetic approach was used in classic syntheses of r (ji)-complexes of various metals [11]. Such syntheses are carried out in two steps preparation, for example, of cyclopentadienyl derivatives of alkali metals with their further application in the syntheses (3.148), (3.149) of sandwich ri5-complexes of mainly transition metals ... 

Alkyl/alkoxide metathesis employing OfBu as alkoxide component revealed to be even more complicated and unpredictable [222-224]. The reactivity of well-characterized (CpR)3 Ln(OtBu)/ species towards alkali metal alkyls seems to be quite sensitive to specific reaction conditions, including choice of solvent, number and type of cyclopentadienyl co-ligands or reaction temperature. 

The synthesis of the first cyclopentadienylberyllium compound was reported by Fischer and Hofmann in 1959 (49). Reaction of cyclopentadienyl alkali-metal compounds with BeCl2 in diethyl ether or benzene leads to dicyclopentadienylberyllium (beryllocene), a rather volatile, colorless, diamagnetic complex, easily soluble in benzene, diethyl ether, and hydrocarbons, and very sensitive to air and moisture. 

In a first approximation supra-Cp metal complexes can be prepared the same way as normal or other Cp-metal and organo-metal bonds in general. The methods used most often (see Appendix) are the metathesis reaction [Eq. (1)] followed in number by oxidative additions (Eq. (2)] and metallation/deprotonation reactions [Eq. (3)]. The latter is especially important for the cyclpentadienyl alkali metal compounds. A useful variation of reaction (3) is the formation of CpTl in an acid/base reaction from cyclopentadiene and thallium ethoxide [Eq. (3b)]. This represents a convenient route to cyclopentadienylthallium compounds, which are also valued (in place of Cp alkalis) as mild Cp-transfer reagents for the synthesis of difficultly isolable cyclopentadienyl derivatives (77). 

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