Fluxionality organometallic compounds

The octahedral complexes, in general, are not fluxional. Organometallic compounds which show fluxional behaviour are as... 

Evidently, we should be wary of drawing conclusions from what may be a deceptively-simple NMR spectrum measured at room temperature wherever fluxionality seems plausible, it must be suspected. Organometallic compounds involving the cyclopentadienide ligand... 

Fluxionality is characteristic of certain classes of organometallic compounds and is found occasionally in others. The phenomenon is seen characteristically in compounds containing conjugated cyclic polyolefins such as cyclopentadienyl, cyclohep-tatrienyl, or cyclooctatetraene, to name the three most common ones, attached to a metal atom through at least one but less than all of their carbon atoms, as illustrated by the following partial structures. 

Chemical shifts have been reported for [Me3CCH2HgX] 203) (see Table XII), tr-allylic derivatives (see Table XIII), o-cyclopentadienyl derivatives (see Table XIV), and miscellaneous compounds (see Table XV). In the case of fluxional a-cyclopentadienyl derivatives, it has been shown that chemical shifts can be used to differentiate between fluxional o-cyclopentadienyl derivatives and w-cyclopentadienyl derivatives 103). The NMR spectrum of [Sb(cyclopropyl)s] has only two carbon resonances, showing that the molecule is fluxional (56) and the NMR spectrum of the naturally occurring organometallic compound, 5 -deoxyadenosylcobalamin, has been reported (65). For a number of norbornane and allylic derivatives of palladium and platinum, a number of linear relationships have been found between chemical shifts of various carbon atoms. It was suggested that a term due to paramagnetic shielding by the metal was dominant 52b). 

Carbon-13-NMR is a routine means of characterizing organometallic compounds, as well as a mechanistic probe [52-56]. The sensitivity of C-NMR is reflected in the wide range of chemical shifts and scalar coupling constants, Jc-x that allows for evaluation of subtle changes in the organometallic species at the M—C bond. This sensitivity has allowed organometallic chemists to evaluate fluxional processes and electron delocalization in... 

This has a low energy barrier ( 25 kJ mol-1) and occurs rapidly ( 2 x 1010 s-1). However, for pyramidal PR3 compounds, the activation barrier has climbed to over 100 kJ mol-1, so inversion is very slow, sufficiently so to even allow enantiomer separation in the case of chiral phosphines. Coordination of the lone pair freezes the configuration. Examples of fluxional complexes tend to be found mostly, but not exclusively, amidst organometallic compounds. Spectroscopic methods, particularly NMR spectroscopy, assist in defining the fluxional behaviour. 

Fluxional behavior is characteristic of certain classes of organometallic compound.32 A few examples have already been considered in Section 1-9 as illustrations a more organized account will be given here,... 

Examples of fluxional behaviour may also be found in organometallic compounds containing more than one metal atom in the molecule, for example (C5H5)(CO)2Mo(C7H,)Fe(CO)3 " and the cluster compound Ru3(C8H8)(CO)4, whose limited solubility unfortunately precludes satisfactory determination of kinetic parameters. " ... 

In connection with investigations on the catalytic activity of organometallic compounds of the rare earths, anionic homoleptic allyl derivatives of Ce, Nd, Sm, Gd and Dy have been prepared according to eq. (47). Allyl lithium was generated in situ from Sn(C3Hj)4 and another lithium alkyl LiL. The compounds, isolated as their dioxane complexes after precipitation from ethereal solution by addition of dioxane, are described as containing fluxional allyl groups from their infrared and H NMR spectra (Mazzei, 1979) ... 

Fluxional Organometallic and Coordination Compounds M. Gielen, R. Willem and B. Wrackmeyer 2004 John Wiley Sons, Ltd ISBN 0-470-85839-7... 

Fluxional organometallic and coordination compounds / edited by Marcel Gielen, Rudolph Willem, Bernd Wrackmeyer. 

Schroder was alert enough to understand what had happened, and went on to a highly successful career that included an examination of the properties of bullvalene and substituted versions of this molecule. Doering s predictions were completely confirmed by Schroder s synthesis. Other neutral, completely fluxional organic molecules have not appeared, although the phenomenon of fluxionality appears to be rather more common in organic cations and organometallic compounds. 

Larrabee, R. B., Fluxional Main Group IV Organometallic Compounds, The Implications for Orbital Symmetry Rules, J. Organometal. Chem. 74 [1974] 313/64. 

Fluxional and Nonrigid Behavior of Transition Metal Organometallic ir-Complexes, 16, 211 Free Radicals in Organometallic Chemistry, 14, 345 Functionally Substituted Cyclopentadienyl Metal Compounds, 21,1... 

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