REACTION OF A RHODIUM(III) ALPHA-CHLOROTOLYL COMPLEX WITH WATER AND OXYGEN - STABLE RHODIUM PEROXO COMPOUNDS

The reaction of the rhodium(III) alpha-chlorotolylcomplex [RhCl2(CHClP h>(2,6-(C(Me)=N-i-Pr)(2)C5H3N)] (1) with H2O and O-2 afforded the rhod ium(III) chloride [RhCl3(2,6-(C(Me)=N-i-Pr)(2)C5H3N)] (11), benzaldehy de, and H2O2 in 80-90% yield. This reaction proceeds via two reaction sequences. First, when O-2 is absent the hydride complex [Rh(H)Cl-2(2, 6-(C(Me>=N-i-Pr)(2)C5H3N)] (2), benzaldehyde, and HCl are formed. Hydr olysis of the metal-bonded CHClPh fragment gives a short-lived CH(OH)P h moiety, which then by beta-H elimination of the hydroxyl group affor ds the products. Alternatively, a rhodium carbene type of intermediate might be involved. The subsequent reaction sequence probably proceeds via two separate pathways. In the first one the hydride 2 may insert O-2 to give a rhodium hydroperoxo species which converts with HCl to t he Rh(III) complex 11 and H2O2. The second pathway appears to involve first the formation of the Rh(I) complex [RhCl(2,6-(C(Me)=N-i-Pr)(2)C5 H3N)] (8) from the hydride 2 in H2O, which subsequently reacts with O- 2 to give the peroxo complex [RhCl(O-2)(2,6-(C(Me)=N-i-Pr)(2)C5H3N)] ( 12). The latter reacts with HCl to give the rhodium(III) chloride 11 a nd H2O2. Both pathways were investigated separately by employing the n ovel hydride 2 and peroxo 12 complexes, which have been prepared in hi gh yields from the rhodium(I) complex 8 with HCl(DCl) and O-2, respect ively. The hydride 2 has acidic character in H2O and is conducting owi ng to dissociation to a small extent into HCl and the rhodium(I) compl ex 8. This solution does react with O-2 in the presence of HCl to from 11 and 80-90% H2O2. The peroxo complex 12, in which O-2 is side-on bo nded, dissolves in H2O to give the weakly basic )(OH2)(C5H3N(2,6-(C(Me )=N-i-Pr)(2)C5H3N)](OH-)-O-+ as two equilibrating isomeric forms which can be converted with HC to 11 and about 90% H2O2. The peroxo complex 12 reacted with SO2 to [RhCl(SO4)(2,6-(C(Me>=N-i-Pr)(2)C5H3N)] (15) b ut not with CO, CO2, and fumaronitrile in dichloromethane. These perox o complexes are the first examples of rhodium peroxo complexes in whic h the O-2 is irreversibly bonded to the rhodium atom.