Cyclopentadienyl metal carbonyls

The present preparation of 5-acetyl-l,2,3,4,5-pentamethylcyclo-pentadiene is more reliable and convenient than that previously available.2 This compound has been used to prepare many pentamethyl-cyclopentadienyl metal carbonyl derivatives3 and is also a convenient source of pentamethylcyclopentadiene for use in preparing other (Me5Cp)mMLn derivatives.4 5... 

CO2MC] were obtained by metal exchange liom (he same ruthenium-dicobalt precursor and analogous functionalized (cyclopentadienyl)metal carbonyl Related reactions of the selenido-containing cluster RuCo2(/r rSe)... 

The design of functionalized polymers with a specific utilization is seen in new polysiloxanes used by Zeldin (p. 199) as phase transfer catalysts. Novel functional polyphosphazenes have been reported as well by Allcock (p. 250). The introduction of transition metal cyclopentadienyl, metal carbonyl and carborane moieties into polyphosphazene macromolecules is representative of truly novel chemistry achieved after careful model studies with corresponding molecular systems. 

In both the examples given above, there is concomitant loss of one or more neutral ligands. Elimination of CO is the rule in reactions of mononuclear metal carbonyls (e.g., entry 12) and cyclopentadienyl metal carbonyls (e.g., entry 4), but not those of polynuclear carbonyls (e.g., entry 16) or carbonyl halides (e.g., entry 33). Elimination of tertiary phosphines often occurs, especially when more than two molecules are present in the initial complex however, this is not always the case (see entry 24). Clearly, steric requirements and the dictates of the 18-electron rule determine the composition of the product, and normally act in concert when they conflict, as in the case of R3SiRuH3(PR3) (n = 2 or 3 entry 22), variable stoichiometry may result. Chelating diphosphines, with somewhat reduced steric requirements, are usually retained (e.g., entry 19), while complexed olefins are invariably lost the bulky ligand P(cyclohexyl)3 is associated with unusual products (entries 47 and 48). Particular mention may be made of the 17-electron species Cl3SiVH(Cp)2 and (Cl3Si)2V(Cp)2 shown... 

Several other twelve-vertex metallocarborane carbonyl complexes have been prepared (51). In general, the chemistry and structures of these species, when investigated, have been found to parallel the analogous cyclopentadienyl metal carbonyls. 

In recent years more and more emphasis has been laid on the chemistry of cyclopentadienyl metal carbonyls. In this field the reactions of cyclopentadienyl metal carbonyl halides with electron donors deserve special attention. Many of these reactions yield cations by replacement of halogen. In the following report, general procedures will be described by which substituted cyclopentadienyliron dicarbonyl cations of the type [C5H5Fe(CO)2L]+ can be prepared. 

Most cyclopentadienyl metal carbonyl compounds are to some extent sensitive to air. The compounds described herein can be exposed to air for a short time however, it is recommended that they should be handled in an inert-gas atmosphere in order to obtain pure samples. Even if there is no decomposi-... 

The reaction of the transition-metal fragments with main group 15 elements directly has proven a very fruitful field for exploration. The methodology has been successful for a wide range of metal complexes. These fall generally into three basic types (1) reactions with cyclopentadienyl metal carbonyls, (2) reactions with homoleptic metal carbonyls and substituted derivatives, and (3) reactions with metal cations in the presence of a multi-dentate chelating ligand. 

E. O. Fischer, W. Hafner, and H. O. Stahl, Uber Cyclopentadienyl-metall-carbonyl-was-serstoffe des Chroms, Molybdans und Wolframs, Z. anorg. allg. Chem. 282, 47-62 (1955). 

Figure 3.7 Representative cyclopentadienyl metal carbonyls (Cp = il-CgRs)...

As with cyclopentadienyl metal carbonyls, the coordination of the net donor arene ligand trans to three 7i-acidic CO ligands confers considerable thermodynamic stability. Relative to the free arene, the coordination of a Cr(CO)3 unit to an arene face removes electron density, to an extent comparable to the inclusion of a nitro ring substituent. The chemical implications of this electron drift from the arene to chromium, and the basis for much chemistry, are an increase in the acidity of protons bound to the arene ring or to the a- and P-carbons of substituents, and... 

Aside from the carbonyl group, the Cp ligand and its analogs are probably the most common ligand systems in organometaUic chemistry. This is also reflected in the large number of cyclopentadienyl metal carbonyl dimers and their derivatives that have been studied. For molybdenum, direct reaction of molybdenum hexacarbonyl and dicyclopentadiene is one of several routes to [CpMo(CO)3]2 (equation 14). 

A method which has been used mainly for the preparation of cyclopentadienyl metal carbonyls, but which is occasionally applicable, is that represented rouglily by the equation... 

The first cyclopentadienyl metal carbonyls to be discovered have the formulas (C6H6)2Co2(CO)4 and (CBHs)2CoFeH(CO)4, but are saltlike compounds having the structures [Co(C5He)2] [Co(CO)4] and [Co(CBHB)2] [FeH(CO)4] (57). For nickel also, the dimer... 

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