Complexation reactions double exchange

The metal-exchange method has been used practically in all syntheses of complexes of closopolyhedral hydroborate anions (Sec. 2.2.5.8). We note that the reactions of double exchange are also applicable to the synthetic aspect (3.151) [314a] ... 

Double exchange reactions of transition metals often involve coordination chain mechanisms (e.g., further reaction of Y, produced by a ligand-initiated pathway, with the initial complex CaX) (Margerum et al., 1978). 

Both of these pathways are disjunctive with respect to the complex ML and may be either adjunctive or disjunctive with respect to the reaction of the intermediate free M or L with the complex M L. The complete dissociation of both initial complexes is an unlikely pathway unless both are weak as may be the case for alkaline earth metal complexes. Double-exchange reactions of transition metal complexes often involve coordination chain mechanisms (for example, further reaction of L, produced by a ligand-initiated pathway, with the initial complex ML) and the overall rates may be strongly dependent on trace concentrations of reactants that promote or terminate coordination chain reactions (Margerum et a ., 1978). 

Maltose phosphorylase proceeds via a single-displacement reaction that necessarily requires the formation of a ternary maltose E Pi (or glucose E glucose-l-phosphate) complex for any reaction to occur. Exchange reactions are a characteristic of enzymes that obey double-displacement mechanisms at some point in their catalysis. 

The reaction of the stabilized yUde 46 (a-vinyl substituted) with the cycloocta-dienyl Pd(II) allows the synthesis of a novel complex, the (rj -allyl)palladium 47, in which the olefmic double bond participates in the coordination (Scheme 20) [83]. The coordination of the bis-yUde 48 with the same starting Cl2Pd(COD) leads to the formation of another new palladium complex 49 via COD exchange reactions. A C-coordination mode takes place between the carbanionic centers of the bis-ylide and the soft palladium and two stereogenic centers of the same configuration are thus created [83]. In contrast to the example described in Scheme 19, the Cl2M(COD) (M=Pd or Pt), in presence of a slightly different car-... 

Several transition metal complexes can catalyze the exchange of partners of two double bonds. Known as the olefin metathesis reaction, this process can be used to close or open rings, as well to interchange double-bond components. 

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