A COMPARISON OF THE NUCLEOPHILICITY OF SULFOXIDES TOWARDS TETRACHLOROPLATINATE(II) AND TETRABROMOPLATINATE(II) ANIONS

Abstract The second order rate constants for the reaction [PtBr4]2- + RR'SO π [PtBr3(RR'SO)]− + Br− (R = CH 3; R' = CH3, C2H5, n-C3H7, 2-ClCH2CH2, C6H5, 4-CH3-C6H4,4-CH3O-C6H4, 4-Cl-C6H4: R = R' = C2H5, n-C3H7: RR' = -(CH2)4-) have been measured in methanol/water (95/5 v/v) at 25.0°C. In general, the rate constants are approximately one order of magnitude greater than those for the corresponding reaction of [PtCl4]2- and mainly reflect the difference in the trans effects of chloride and bromide. Although the rate constants are very sensitive to the bulk of the substituents R and R' on the sulfoxide there are no enhanced steric effects arising from the replacement of Cl by Br. This is in direct contrast to the reactions of [AuX4]− with amines where only the X = Br complex shows steric hindrance in its reaction with 2- and 2,6- substituted heterocyclic nitrogen bases.

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