Orbital occupations metallocenes

Frontier orbitals of metallocenes containing parallel Cp ligands (the electron occupancy shown is that of ferrocene) the spin states of several metallocenes. 

F CP2 CoCpj CoCp2 NiCp2 FIGURE 5.5 The orbital occupation patterns for some first-row metallocenes. 

Fig. 15.33 Qualitative molecular orbital diagram fora metallocene. Occupation of the orbitals enclosed in the box depends on the identity of the metal, for ferrocene it is e L-[From Lauher, J. W. Hoffmann. R. J. Am. Cfie/n. Soc. 1976. 98, 1729-1742. Reproduced with permission.)...

FIGURE 5.6 The bent metallocenes, (a) Note how all these metallocenes have three orbitals directed as shown for 5.28. (b) The occupancy of these orbitals depends on how many electrons the metal provides. For Ti, the center orbital is left empty. This can act as a Lewis acid as shown in (c), where the Ti is interacting with a lone pair of a Tt-basic ligand, For Mo, this orbital is filled, and so can act as a Lewis base in (c) it is shown in back donation to a ir-acid ligand, ethylene. 

The examples where jlSR provides Arrhenius parameters similar in magnitude to those measured by NMR and QENS are summarized in Table 7.3. The xSR measured dynamic process in all these cases is likely to be the same as that measured by the other two techniques, namely the metallocene (benzene or cyclopentadien) ring rotation. The detailed investigation of ferrocene illustrates how this can be rationalized on the basis of the occupancy of a nonbonding orbital, with respect to the dynamic process, by the unpaired electron of the radical species. These were named as the electron playing a passive role. 

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