Bonding ferrocene

The pattern shown is only one of a large number of distinct ways of choosing the L/X labels in (4.122) and (4.123), corresponding to the large number of equivalent resonance structures that could be written. However, such an exercise adds little value to the simple picture of ferrocene bonding provided by the localized bonding units. 

An X-ray structural study of the ferrocenylphosphonium salt (147) shows a significant shortening of the phosphorus-ferrocene bond, lending support to an earlier suggestion by McEwen that there may be overlap of the filled hog MO of the ferrocenyl group with an empty 3d orbital of phosphorus. The possible existence of an equilibrium between the substituted methylphosphonium salts (148) and the cationic phosphorane system (149) has been ruled out following spectroscopic and structural studies of a series of such salts. ... 

The effects of the nature of the nitrogen donor atom vs. sp ) upon the properties and chemistry of palladated complexes with cr(Pd-G(i/) )), ferrocene) bonds were studied by Lopez et Mossbauer spectra show that... 

Figure 2-47. The bonding in organometallic coinplexes (e.g., ferrocene) cannot be expressed adequately by a connection table,...

Ferrocene Figure 2-47) provides a prime ex.ample of multi-haptic bonds, i.e, a situation where the electrons that coordinate the cyclopentadienyl rings with the iron atom arc contained in molecular orbitals delocalised over the iron atom and the 10 carbon atoms of the cyclopentadienyl rings [82. ... 

Ferrocene (Figure 2-61a) has already been mentioned as a prime example of multi-haptic bonds, i.c, the electrons tlrat coordinate tire cyclopcntadicnyl rings with the iron atom are contained in a molecular orbital delocalized over all 11 atom centers [811, for w hich representation by a connection table having bonds between the iron atom and the five carbon atoms of cither cyclopcntadicnyl ring is totally inadequate. 

Indeed ferrocene was firsf prepared by adding iron(II) chloride fo cyclopenfadienyl sodium Insfead of fhe expecfed a bonded species shown m fhe equafion ferrocene was formed... 

Section 14 14 Transition metal complexes that contain one or more organic ligands offer a rich variety of structural types and reactivity Organic ligands can be bonded to a metal by a ct bond or through its it system Metallocenes are transition metal complexes m which one or more of the ligands is a cyclopentadienyl ring Ferrocene was the first metallocene synthesized Its electrostatic potential map opens this chapter... 

Appllca.tlons. The first widely appHcable Ic separation of enantiomeric metallocene compounds was demonstrated on P-CD bonded-phase columns. Thirteen enantiomeric derivatives of ferrocene, mthenocene, and osmocene were resolved (7). Retention data for several of these compounds are listed in Table 2, and Figure 2a shows the Ic separation of three metallocene enantiomeric pairs. P-Cyclodextrin bonded phases were used to resolve several racemic and diastereomeric 2,2-binaphthyldiyl crown ethers (9). These compounds do not contain a chiral carbon but stiU exist as enantiomers because of the staggered position of adjacent naphthyl rings, and a high degree of chiral recognition was attained for most of these compounds (9). 

Other types of bonding include donation by Ligand TT-orbitals, as in the classical Zeiss s salt ion [Pt( 7 -CH2=CH2)Cl3] [12275-00-2] and sandwich compounds such as ferrocene. Another type is the delta (5) bond, as in the Re2Clg ion, which consists of two ReCl squares with the Re—Re bonding and echpsed chlorides. The Re—Re 5 bond makes the system quadmply bonded and holds the chlorides in sterically crowded conditions. Numerous other coordination compounds contain two or more metal atoms having metal—metal bonds (11). 

The structure of ferrocene and an MO description of its bonding have already been given (p. 937). The rings are virtually eclipsed as they are in the analogous ruthenocene (light-yellow, mp 199°C) and osmocene (white, mp 229°C). 

Next, consider how Fe " interacts with C5H5. Examine the geometry of ferrocene, Fe(C5H5)2. Are the FeC distances all the same, or does iron bond more strongly to some carbons than to others Are the CC bond distances all the same Which of the above models, the electrostatic or covalent, gives the better description ... 

Asymmetric catalysis using chiral ligands, including cyclic phosphine or pyra-zole fragments covalent-bonded with ferrocene system 98PAC1477. 

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