STOICHIOMETRY AND KINETICS OF ACID CLEAVAGE OF SOME SINGLE-BRIDGED BINUCLEAR CHROMIUM(3) COMPLEXES

The stoichiometry and kinetics of the cleavage of the rhodo ion, (NH3)5Cr(OH)Cr(NH3)6, the aquoerythro ion, (NH36Cr(OH)Cr(NH3)4OH2, and the chloroerythro ion, (NH3)5Cr(OH)Cr(NH3)4Cl4+, by aqueous HC1O4 have been studied. The products of the cleavage reactions are (NH3)5CrOH2 from the rhodo ion, (NH3)5CrOH2 and cis-(NH3)4Cr(OH2)2 from the aquoerythro ion, and (NH3)5CrOH2 and trans-(NH3)4Cr(OH)2Cl2+from the chloroerythro ion. The cleavage rates are independent of [H+] in 0.1-1.0 M HCIO4, the rate law being -d[dimer]/dt = & [dimer], where k = (7.6 ± 0.1) × 10-4 sec-1 at 55.0° and Ea = 28.7 ± 0.3 kcal mol-1 for the rhodo ion; k = (11.8 ± 0.4) × 10-4 sec-1 at 55.0° and Ea = 28.1 ± 0.3 kcal mol-1 for the chloroerythro ion; k = (4.0 ± 0.3) × 10-4 sec-1 at 65.0° and Ea = 28.7 ± 0.4 kcal mol-1 for the aquoerythro ion, all at μm = 1.00M. The cleavage of the aquoerythro ion becomes more rapid in the presence of Cl-, and cis-(NH3)4Cr(OH2)Cl2+ is found among the products. It is postulated that the aquoerythro ion reacts with Clto give the cis-chloroerythro ion, which cleaves more rapidly than the aquoerythro ion. © 1969, American Chemical Society. All rights reserved.