Fluxional Systems

The seven-co-ordinate [W(CO)3(L)a] (L=dimethyldithiocarbamate ion) shows three n.m.r. resonances at 163 K. On raising the temperature, two of these resonances coalesce independently of the third (AC = 8.1 kcal mol ) and at still higher temperatures all three resonances merge (AG =9.0kcal mol ). Both processes involve intramolecular isomerism. A series of seven-coordinate complexes of the type [MoCNjRXSaCNMea),] [R= aryl (1)] are also fluxional, and the activation parameters for the dynamic process which is observed are collected in Table 3. Simultaneous collapse of all of the methyl resonances is involved. A good correlation between the logarithm of the observed 

A number of fluxional eight-co-ordinate complexes of the type [ML4] [M= or Th, L = dipivaloylmethanate or dibenzoylmethanate M = Zr ,  

Reviews dealing with aspects of the stereochemistry of six-, seven-, and eight-co-ordinate complexes have appeared.  

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The open face comprises a fluxional system involving the two atoms and the endo-Hi atom of the BH2 group)... 

The various derivatives of another fluxional system, i.e. semibullvalene 549, have been described in a series of publications280-283. To estimate the influence of substituents at... 

Some representative examples follow. The H-NMR spectra of diallylzinc (19), bis(2-methylallyl)zinc (20), bis(3-methylallyl)zinc (21) and bis(3,3-dunethylallyl)zinc (22) are typical fluxional systems whose dynamics have been studied over the range of temperatures —125 °C to 100 °C. Diallylzinc (19) shows the four a- and y-protons as chemically... 

For simplicity s sake, both potential wells lire shown to be the. same depth. In general for a hydrogen bond such as —O—H — N this is not I rue. All of the configurations of a truly fluxional system are energetically equivalent, however, and have equivalent potential wells. 

A novel fluxional system has been recently investigated in which the interaction of ethylene with metal clusters produces species such as H20s3(C0)9(C=CH2). Rearrangements in these species, as well as those in benzyne complexes, such as Os(CeH4)P(CH3)2(CO)7 (45), have been reviewed by Lewis and Johnson (55). 

NjP3(MeNCH2CH20)2(dmp)2 P[Pg.328]

The concept of dynamic NMR and in particular stereochemical nonrigidity has been dealt with previously by many authors. A recent volume [219] contains a section relevant to phosphine complexes and is therefore especially noteworthy however, as we have just introduced a five coordinate potentially fluxional system in which the... 

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