Studies of the Ruthenium(III) Complex. V. Aquation and Anation Reactions of Halogenoacetatopentaammineruthenium(III) Complexes in Aqueous Solutions

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The kinetics of aquation and anation reaction have been studied with pentaamineruthenium(III) complexes containing halogenoacetates (fiuoro-, monochloro-, dichloro-, trichloro-, bromo-, and iodoacetates). It has been found that the aquation reaction proceeds through two kinds of paths, i.e. the acid-catalysed path and the aciduncatalysed path, except the cases of dichloro- and trichloroacetate complexes. The aquations of dichloro- and trichloroacetate complexes are not catalysed by a proton because these ligand acids are strong acids. The equilibrium constants between [RuH2O(NH3)5]3+ and [RuO2CRX(NH3)5]2+ (O2CRX=halogenoacetate), Keq, were calculated from the anation and aquation rate constants. The kaq and Keq values for the fiuoro-, chloro-, dichloro-, trichloro-, bromo-, and iodoacetatocomplexes are, respectively: kaq, 10×10−5, 7.5×10−5, 19.1×10−5, 49.0×10−5, 6.8×10−5 and 6.7×10−5 sec−1; Keq, 5.2×10−3, 3.6×10−3, 9.0×10−3, 23×10−3, 3.5×10−3, and 3.3×10−3 M, at 60°C. The free energy plot, logkaq vs. logKeq, gave a straight line with a gradient of 1.0. It has been concluded that the acid-uncatalysed reaction proceeds via a SN1 mechanism, while the acid-catalysed reaction seems to take place with a SN2 mechanism. Some remarks have been made on the molecular interaction between the complex and the acid catalyst.
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