Cyclopentadienylmetals

A. Metal carbonyl anions/cyclopentadienylmetal carbonyl anions... 

Belonging to group (i) are alkylmetal carbonyls and cyclopentadienylmetal alkyl carbonyls of formula RMn(CO)5, CpFe(CO)2R, and CpMo(CO)3R. Solvent dependence of the reaction of MeMn(CO)5 with CjHi,NH2 is illustrated also in Table I. The rate varies markedly with the dielectric constant and with the nucleophilic power of the solvent. For example, on going from dimethylformamide to mesitylene, the rate of insertion is reduced by 10. Similarly, the sequence MeCN > MejCO > THF > CHCI3 > CjHj was reported for the reaction of MeMn(CO)5 with P(0CH2)3CR (R = Me and Et) in various solvents (97). Analogous trends were observed for the insertion reactions of CpFe(CO)2R and CpMo(CO)3R (48, 80, 98). 

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. 

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... 

Alkali metal hydrides can be used as metallating agents in the synthesis of base-free cyclopentadienylmetal derivatives.27 28... 

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

The mass spectra of binuclear cyclopentadienylmetal carbonyl derivatives of chromium and molybdenum provide useful indications of the relative strengths of the metal-metal bonds in various compound types. The mass spectrum of [C5H5Cr(CO)3]2 (S. M = Cr) exhibits no bimetallic ions but only monometallic ions such as CsHsC CO) (n = 3,... 

A more sophisticated approach has been used by Winters and Kiser (199) to calculate the heats of formation of the cyclopentadienylmetal carbonyls C5H5V(CO)4, C5H5Mn(CO)3, and C5H5Co(CO)2 as well as the heats of formation of some of the fragment ions. The heats of formation were calculated for the process... 

New group 4 cyclopentadienylmetal (equation 62)188,189. carbonylate derivatives were also reported... 

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). 

The acidity of the cyclopentadienes makes the cyclopentadienyltin compounds readily accessible97 either through the reaction of other cyclopentadienylmetal derivatives with tin(IV) halides (equation 9-44),99 or by acidolysis of an aminostannane with a cyclopentadiene (equation 9-45).100 101 Ferrocenylstannanes can also be obtained from ferrocenylmercury compounds and organotin sulfides (equation 9-54).102... 

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). 

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