Cyclopentadienyl-metal complexes monocyclopentadienyls

An analogy may be drawn between the monocyclopentadienyl complexes such as 7r-CBH6M(CO)3R (XXVI), where M = Mo or W, and R = alkyl, and the bis(7r-cyclopentadienyl) metal complexes. The three carbon monoxide groups in the complexes (XXVI) may be compared with a 7r-cyclopenta-dienyl group, in that they occupy three coordination positions of the metal... 

Probably substitution of the cyclopentadienyl ligand on alcoholysis and hydrolysis, and its transfer in reactions of di- and monocyclopentadienyl-titanium derivatives with FeClj or iron(II) acetylacetonate, follows a mechanism common for 77-ligand exchange in other metal 77-complexes (see later). 

The group of monocyclopentadienyl metal carbonyls is the most extensive. In this, in contrast to the pure cyclopentadienyl compounds, it is found that complexes are formed only by transition elements of groups 5 to 8, i.e., metals which can enter into true ferrocene-type bonding. There is a regular relationship for this series transition elements of odd atomic number yield readily volatile compounds of formula CsHsMefCO) , while the even-numbered members form dimers of composition [CsH6Me(CO)ic]2. The actual value of x, the number of ligand carbon monoxide molecules, corresponds to the number of pairs of elec-... 

Bis(cyclopentadienyl)iron derivatives, ferrocenes, are remarkably stable against heat and air and undergo various kinds of chemical reactions. They are usually prepared by the reaction of FeCh with an alkali metal salt of cyclopentadienyl or cyclopentadiene in the presence of base [51]. Although ferrocene derivatives basically have chemical reactivities similar to those of aromatic compounds, they have found only limited applications to organic synthesis so far. However, because chiral ferrocenylphosphines are capable of having both planar chirality and an asymmetry in the side chain in their rigid framework, they have been used recently in a number of asymmetric reactions. In this section, synthesis and developments of monocyclopentadienyl complexes and ferrocenylphosphines are described. The general chemistry of ferrocenes and half metallocene complexes is reviewed elsewhere [52-53]. 

---