Oxidative Additions Involving Ligand Bond Cleavage

4 Oxidative Additions Involving Ligand Bond Cleavage 

The substitution of triosmium dodecacarbonyl by arsine and phosphine derivatives under mild conditions yields a series of simple substitution products. 

Thermal treatment of these products often leads to a series of processes such as 

Another example of orthometallation is the series of reactions shown in Fig. 2.65. The thermal treatment of the compound Os3(CO)n(PPh2R)(R = Ph or Me) induces loss of carbon monoxide providing cluster unsaturation which promotes in turn the activation of a C-H bond in the phosphine giving finally Os3(CO)9( 3-C6H4)(/i3-PR). The metallation of two carbon atoms observed in 

The orthometallation process and the possibility of stabilizing fragments RP by bonding to the metal framework make this oxidative addition with cleavage of the strong phosphorus-carbon bond possible. 

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The experimental results that both branched and linear allylic ethers are obtained in the palladium-catalyzed decarboxylation of branched allylic carbonate indicate occurrence of direct oxidative addition involving the C-0 bond cleavage followed by the nucleophilic attack of the alkoxide liberated on either the substituted or non-substituted terminus of the allylic ligand (Scheme 4) [1]. 

Oxidative addition and reductive elimination are the formal chemical processes involving oxidation and reduction of metal atoms accompanied by bond cleavage and formation between ligands A and B, respectively, as shown below. Thus, since A and B are one-electron ligands, the oxidation statte, electron count, and coordination number increase by two units in the oxidative addition. Oxidative addition to dinuclear or 17-electron complexes results in change of the oxidation state, electron count, and coordination number increase by one unit. The reductive elimination is the inverse process of oxidative addition and vice versa. 

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