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Chlorotris(triphenylphosphine)rhodium (I) exists in benzene as RhCl(PPh3)3, a dimeric species [RhCl(PPh3)2]2 and a reaction intermediate RhCl(PPh3)2. The rates of oxidative addition and replacement reactions were examined in benzene. For the oxidative addition reaction, RhCl(PPh3)3, RhCl(PPh3)2, or [RhCl(PPh3)2]2+X1\oversetkadd\ightleftarrowsProducts (X1=H2, O2, C2H4, CHCl=CCl2 CH3I), it was found that the reaction intermediate RhCl(PPh3)2 is most reactive, the degree of its reactivity depending largely on the reactants (X1). A significant enhancement of the rate (ksub>kadd) was observed for the ligand substitution reaction, RhClX1(PPh3)m+X2\oversetksub\ightleftarrowsRhClX2(PPh3)n+X1 (m, n=3 or 2), where X1=H2 and X2=olefin and vice versa. The results are discussed in relation to the mechanism of hydrogenation.

The kinetics of the substitution reactions of RhCl(NCCH3)(PPh3)2 in benzene was studied at 20 °C by the stopped-flow method under anaerobic conditions. The following mechanism was proposed: (Remark: Graphics omitted.)