Kinetics of the Oxidative Addition of Hydrogen to Chloro(acrylonitrile)bis(triphenylphosphine)rhodium(I) in Benzene

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Abstract
The reaction between chloro(acrylonitrile)bis(triphenylphosphine)rhodium(I) and hydrogen was studied by the stopped-flow method under an anaerobic condition. A solution of RhCl(CH2=CHCN)(PPh3)2 was mixed with a benzene solution containing hydrogen under the condition of [Rh]<[H2]0<[CH2=CHCN]. A fast decrease in the absorbance was followed by a slow increase in the absorbance, until finally the absorbance returned to the initial value. It was proved that the faster reaction was the oxidative addition of hydrogen to RhCl(CH2=CHCN)(PPh3)2; RhCl(CH2=CHCN)(PPh3)2+H2\oversetk34\undersetk43\ightleftharpoonsRhClH2(CH2=CHCN)(PPh3)2. The slower reaction was the process in which hydrogen was consumed in the course of the hydrogenation of acrylonitrile and RhCl(CH2=CHCN)(PPh3)2 was reproduced. The values of the rate constants were evaluated to be k34≥7.8×103 mol−1 dm3 s−1 and k43≤53 s−1.