Exchange dissociative

Interchange of Atoms Vacancy Hopping Interstitial Movement Dissociative Exchange... 

The present article is a review of tt complex adsorption which has recently been proposed in catalytic reaction mechanisms (2-11). The main evidence for this intermediate has been obtained from isotopic hydrogen exchange reactions with aromatic compounds where an interpretation according to classical theories has met with increasing difficulties. The limitations of the classical associative and dissociative exchange mechanisms originally proposed by Horiuti and Polanyi (12) and Farkas and Farkas (13-15) re discussed. This is followed by a... 

The importance of the strength of tt complex adsorption on the reaction rate through the operation of displacement effects is further demonstrated by naphthalene randomization reactions. Naphthalene exchanges very slowly with deuterium oxide. That this is due to the displacement of water by normal naphthalene and not due to a toxic side reaction, such as polymerization, is shown in randomization experiments with mono a-deuterated naphthalene. Randomization is completed within 24 hours at 120°, whereas no significant deuteration occurs under the same reaction conditions with water. This result furnishes additional proof for the dissociative exchange mechanism. 

The incorporation of metals into metal-free porphyrins has been reported to proceed by a dissociative mechanism.278 The porphyrin and metal form an outer-sphere complex, the porphyrin nucleus deforms to provide a suitable configuration to complex with the metal ion, and then dissociative exchange occurs as shown ... 

The kinetic data from phosphine dissociation studies and reaction with ethyl vinyl ether fit the classical dissociative exchange catalysis model very well [101]. Examination of this model leads to the conclusion that there are two main factors controlling the activity of these catalysts the rate of phosphine dissociation and the metathesis activity of the phosphine-dissociated species (Scheme 6.26). 

The CT-alkylplatinum(rV) complex reacts with nucleophiles X (H2O, CE) to afford an alcohol ROH and an alkyl chloride RCl, respectively. Complexes VI-5 and VII-7 (R = CH3 or CH2CH2OH) in aqueous solutions containing excess chloride have been shown [29b] to exist in equilibrium with X = 0.9 mol dm at 25 °C. Rapid dissociative exchange of ligand trans to the alkyl substituent was proposed to occur via the five-coordinate intermediate VII-6. 

Bribre. K.M. Detellier. C. Solvent effects in the metal interchange of crown ether-alkali metal cation complexes. Transition from an associative exchange in nitromethane to a dissociative exchange in acetonitrile studied by Na... 

The diffetentiation of the dissociative and intramolecular mechanisms is usually based on a comparison of the rates of ligand dissociation (exchange or solvolysis) and racemization. If the rates are quite similar, dissociation is assumed, whereas if racemization is much faster, then an intramolecular mechanism is operating. However, this involves the implict assumption that the initial chelate ring opening step is rate limiting for both fnocesses. 

Infrared analysis indicates that the photolytically assisted mono- or di-substitution of CO in [M(CO)4(nbd)] (M = Cr, Mo, or W nbd = norbomadiene) occurs stereospecifically in the axial position(s). On standing in the dark conversion into the equatorially substituted complexes takes place. The proposed mechanism initially involves dissociative exchange with labelled carbonyl, and subsequently axial-equatorial equilibration of carbonyls via opening of the norbomadiene chelate ring, rather than by carbonyl scrambling. A brief report of intermolecular redistribution... 

In contrast to the 17-electron Cp 2V(C0) complexes which show associative CO exchange, CpV(n -pentadienyl)(CO) shows dissociative exchange.The related indenyl complexes (indenyl)2V react with CO to give products such as (ind)2V(CO)2 the first... 

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