Fluxional molecule organometallic

Stereochemical Nonrigidity of Organometallic Complexesf This feature has generated interest with respect to fundamental mechanisms of intramolecular migrations and the possible participation of fluxionality in transformations on clusters. However, fluxionality see Fluxional Molecule) can frustrate the characterization of new compounds. 

Cotton, F. A., Frenz, B. A., Deganello, G. Shaver, A. (1973) Fluxional organometallic molecules. XXXIV. The structure and temperature-dependent NMR spectrum of cis-(l,2,6-trihap/o- 3,4,5-fri/iapto-bicyclo[6.2.0]deca-l,3,5-lriene)hexacarbonyldi iron(Fe—Fe)," J. Organomet. Chem. 50,227-240. 

Molecular Motions and Dynamic Structures. Molecular motions are of quite general occurrence in the solid state for molecules of high symmetry (22,23). If the motion does not introduce disorder into the crystal lattice (as, for example, the in-plane reorientation of benzene which occurs by 60° jumps between equivalent sites) it is not detected by diffraction measurements which will find a seemingly static lattice. Such molecular motions may be detected by wide-line proton NMR spectroscopy and quantified by relaxation-time measurements which yield activation barriers for the reorientation process. In addition, in some cases, the molecular reorientation may be coupled with a chemical exchange process as, for example, in the case of many fluxional organometallic molecules. ... 

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). 

F. A. Cotton Accounts Chem. Res. 1, 257 (1968) Fluxional organometallic molecules 9 (49) Author s work reviewed... 

Organometallic Molecules. Many organometallic molecules involving unsaturated organic groups are fluxional. More detailed discussion and references will be found in Chapter 23, but a few illustrative examples may be cited here. 

The dynamic behavior, or fluxionality, of metal carbonyl clusters (and indeed of organometallic molecules in general) was first recognized with the advent of nuclear magnetic resonance spectroscopy, especially C An early example of... 

Fluxional and other stereochemically nonrigid organometallic molecules were the subject of extensive reviews by Cotton et al. 24, 31) and Vrieze (/06) these reviews cover the literature through mid-1973 70). 

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. " ... 

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. 

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