Rhodium complexes reaction with sulfur dioxide

Reaction with sulfur dioxide yields a o--allylic rhodium-sulfur dioxide complex (1). 

The [Rh(NH3)5(OH)] cation, and its chromium(III) analog, react very rapidly with sulfur dioxide in aqueous solution, to give O-sulfito complexes, which lose sulfur dioxide on addition of acid. Rate constants for reaction of the rhodium(III), chromium(III), and cobalt(III) complexes [M(NH3)5(OH)] with sulfur dioxide are 1.8 x 10, 2.9 x 10, and 4.7 x 10 dm mol" s", respectively. This great similarity of rates contrasts with the situation in respect of formation of carbonato complexes, where formation rate constants show a marked dependence on the p a of the aquo form of the hydroxo substrate. 

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