Cyclopentadienylmetal complexes

Cyclopentadienyl (Cp) ligands, 16 79 Cyclopentadienylmetal complexes, 16 79 re-Cyclopentadienyl nickel complexes,... 

Several preparations of silylated cyclopentadienylmetal complexes involve the formation of a triorganosilylcyclopentadienyl anion (by treatment of a silylated cyclopentadiene with an alkali metal in tetrahy-drofuran or by metalation with n-butyllithium), followed by reaction with metal chlorides. This type of reaction has been used for the synthesis of silylated ferrocenes (41, 43, 58, 83, 84, 103, 107, 116, 135, 142, 171, 172), cobaltocenes (135), nickelocene (135), titanium cyclopen-tadienyls (46, 145), and cyclopentadienylmanganese tricarbonyl (30) [Eqs. (19) and (20)]. It is remarkable that Si—C5H6 bonds are not... 

Substituted ferrocenes also form monoanions at very negative potentials electron addition is genuinely associated with the ferrocene nucleus rather than with an electroactive substituent. The E° value for [Fe(f/-C5H4Ph)2] is — 2.62 V, and [FeCp2] itself shows a quasi-reversible reduction at —2.93 V in dmf (452), with a peak separation of 250 mV at — 37°C(v = 1 Vsec-1). Exhaustive electrolytic reduction of ferrocene derivatives yields solutions containing the substituted cyclopentadienide anions the latter may be used in the syntheses of other cyclopentadienylmetal complexes (453). Ferrocenes are also finding use as mediators in electron-transfer reactions, especially at electrode surfaces (454-456). 

Since the C5HJ anion functions as a uninegative ligand, the di-/z5-cyclopentadienylmetal complexes are of the type [(/z5-C5H5)2M]Xn 2,... 

Cyclopentadienylmetal Complexes Bearing Pendant Phosphorus, Arsenic, and... 

Reviewing the literature in the field of cyclopentadienylmetal complexes bearing pendant phosphorus, arsenic, and sulfur ligands is timely given that the number of publications of relevance to this topic is growing exponentially as can easily be seen from the list of references in this review the number of references since 1993 clearly exceeds that of all years before. The reason for this development may be that cyclopentadienylmetal complexes bearing pendant... 

This review covers the chemistry of cyclopentadienylmetal complexes, in which the cyclopentadienyl ligand bears a sidearm which includes a phosphorus, arsenic, or sulfur ligand. The pendant ligand has to be separated from the cyclopentadienyl part, that is. 

The field of cyclopentadienylmetal complexes bearing pendant arsenic or sulfur ligands has remained rather limited up to date. Flowever, their difference from the corresponding phosphane and oxygen representatives could, possibly in combination with other pendant ligands, become a basis for interesting developments in the future. 

H. Butenschdn, Cyclopentadienylmetal complexes bearing pendant phosphorus, arsenic, and sulfur ligands. Chem. Rev. 100,2000 1527. 

The main goal of this chapter is to give a brief overview of reactions that have been catalyzed by cyclopentadienylmetal complexes and to show their potential and application in organic synthesis. The reactions have been classified into seven types according to their similar features. The tables give some representative examples of chemical transformations. In some cases presumed reaction mechanisms are also shown for better understanding of the course of the reaction. It is necessary to emphasize that the list of the reactions and possible applications is by no means final and many new interesting applications and reactions can be expected to appear in the near future. 

Generally speaking, other cyclopentadienylmetal complex catalyzed carbo-metallations of alkynes are rather rare but a few interesting examples have been reported. The first one is the zirconocene 1 catalyzed ethylmagnesation of dialkyldiynes with ethylmagnesium bromide to afford a mixture of isomeric enynes 34 (Scheme 14). The ethylation proceeds regioselectively on the terminal carbon atom of the diyne moiety. However, the addition is not stereoselective a mixture of cis and trans isomers is obtained [22]. 

The reactivity of these metal hydride-metal carbonyl reactions can be correlated with the nature of the reactants in a manner consistent with the proposed mechanism nucleophilic attack by hydride on coordinated CO. Thus reactions involving the highly nucleophilic group IV hydride, Cp gZrHg, are much faster than those of group V metal hydrides. On the other hand, the relatively electrophilic neutral binary metal carbonyls all react with Cp2NbH under mild conditions (20-50° C), whereas more electron-rich complexes such as cyclopentadienylmetal carbonyls (Cp2NbH(C0), CpV(CO) ) or anionic carbonyls (V(CO)g ) show no reaction under these conditions. 

Fig. 20. Bis( 7)5-cyclopentadienylmetal)(fi-1,3-diborolene) triple-decker sandwich complexes (78—81).

Preliminary data have been reported 154) which show that [ Co(/i3-As)Cp 4] is oxidized to the mono- and dications. In addition, it is the first cyclopentadienylmetal-cubane complex to be reduced to a genuine monoanion. 

The possibility of performing metal-catalyzed desulfurization under PTC conditions was first demonstrated for thiobenzophenones. These compounds were reacted with cyclopentadienylmetal carbonyls in a benzene/aq. NaOH system containing a PT agent [189]. Fulvenes and disulfides are formed in the presence of iron complexes (cf. Section 3.2.13). 

With respect to cyclopentadienyl metal complexes ligands other than the cyclopentadienyl (Cp) ligand are frequently regarded as less important and are considered to leave the molecule before the critical reaction step at the cyclopentadienylmetal nucleus. It is remarkable that Trost et al. found that reactions involving the 1,5-cyclooctadiene (COD) ligand for the construction of a carbon skeleton are indeed possible. [2]... 

Molecular rotation in the cavity has been discussed for many compounds using nmr(8,9), esr(lO) and Mossbauer spectroscopy(4,5). A complete description of the Mossbauer spectrum for such a case has been given by Gibb(4) for that of the 3 1 clathrate of thiocarbonyl diamide and bis( -cyclopentadienyl)iron(II). Evidence for conformational isomerism has been presented recently based on the ir spectra of y-cyclopentadienylmetal carbonyl complexes such as CpFe(CO) SiCl Me(ll), ip -MeC H Mn(CO) (P(OMe) )(12) and others(13), and on the Mossbauer... 

Mono-TT-cyclopentadienylmetal nitrosyl and carbonyl complexes 7i-Cyclopentadienylnickel nitrosyl [1-13]... 

Arene cyclopentadienylmetal and arene metal carbonyl complexes are two other classes of materials that are metallocene-like in structure. The first report of the synthesis of tiie T) -mesitylene-Ti -cyclopentadienyliron cation in 1957 by Coffield et al. was a seminal event in this research field. However, it was the 1985 report on the polymerization of T -dichlorobenzene-Ti -cyclopentadienylruthenimn with diphe-nohc compounds, forming compounds such as 10, by Segal that caused research in this area to expand. 

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