Reductive Eliminations to Form -X Bonds from Aryl and Alkylplatinum IV Complexes

Reductive Eliminations to Form C-X Bonds from Aryl and Alkylplatinum(IV) Complexes 

Equations 8.56-8.58 display several examples of reductive eliminations to form carbon-heteroatom bonds from Pt(IV). Reductive elimination of phenyl iodide occurs from a Pt(IV) diphenyl diiodide complex (Equation 8.56). - This reaction is preceded by dissociation of iodide to generate a cationic Pt(IV) intermediate, as shown by inhibition of the reaction rate by added iodide. Elimination after dissociation of the iodide is favored by the five-coordinate geometry and by the reduced electron density on the cationic metal center. 

Studies of the reaction in Equation 8.57 show that reductive elimination of methyl iodide from alkylplatinum iodide complexes also occurs after dissociation of halide. - These reductive eliminations occur between groups originally located in mutually trans positions. This result is consistent with the stereochemistry of the Pt(IV) product from oxidative addition by an S 2 path. The selectivity of the cationic intermediate for reductive 

Like the rates of reductive eliminations to form C-H and C-C bonds, the rates of reductive eliminations to form carbon-heteroatom bonds depend on the coordination number of the metal. The reductive elimination to form C-N bonds from Pd(0) has been shown to occur faster from three-coordinate complexes than from four-coordinate com-plexes. - The reaction of the triphenylphosphme complex in Equation 8.63 to form triarylamine and Pd(0) was conducted with varying concentrations of added ligand. The rate of the reaction was slower when conducted with higher concentrations of added PPhj. A detailed study of the dependence of the rate of reaction on the concentration of added PPhj revealed two pathways for reductive elimination of amine—one from a four-coordinate cis complex and one from a three-coordinate complex formed by dissociation of phosphine. Although the relative rates of these two pathways depend on the concentration of added ligand, reaction through the three-coordinate intermediate was the major pathway at the concentrations of free ligand that would be present in most reactions. 

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