The ion cis-[Rh(bipy),CI,]+ (bipy = 2.2'-bipyridyl) is reduced in alkaline aqueous ethanol under hydrogen to the known [Rh(bipy),]+ ion. A detailed kinetic study of this reaction has been carried out and the rate equation governing the reaction is shown to be of the form dThe observed rate constant varies with hydroxide-ion concentration, but is independent of the concentration of added chloride ion. The variation of rate with temperature is also reported. A mechanism is postulated to account for the experimental results.
The uptake of oxygen by aqueous solutions containing 1.2-diaminoethane and various cobalt(1i) salts is shown to be rapid, with these reagents interacting in the stoicheiometric ratios of 1 : 5 : 2 respectively to give the p-peroxop-diaminoethano-tetrakisdiaminoethanedicobalt(ll~) cation (B). This compound slowly equilibrates with the analogous p-peroxo-p-hydroxo-species (C), while it may be oxidised to a p-superoxo-p-diaminoethano-complex (A). These complexes have been examined by a variety of physical techniques and solutions of the p-peroxospecies have been shown to react with gaseous carbon dioxide to yield the carbonato-bisdiaminoethane-cobalt-of Aston in Birmingham, Gosta Green, Birmingham 4 THERE has been much interest recently in the reaction of both as simple models of reversible biological oxygen molecular oxygen with transition-metal cornplexes,l carriers 2 9 3 and as a source of binuclear bridged peroxo-4-6
The compound [RhI"(DH) (DH,) CI,] (DH, = dimethylglyoxime) is reduced in alkaline aqueous ethanol under an inert atmosphere to a rhodium(i) complex. A detailed kinetic study of this reaction has been carried out and the rate equation governing the reaction shown t o be of the form dThe observed rate constant varies with the inverse fourth power of the hydroxide-ion concentration, but is independent of the concentration of added chloride ion. The variation of rate with temperature is also reported. A mechanism is postulated to account for the experimental results.ALTHOUGH bis(dimethylg1yoximato)cobalt complexes have been extensively studiedJ1p the analogous rhodium complexes have received relatively little attention. Recently these systems have become a topic of interest to several workers3-s and compounds are known which contain rhodium in the oxidation states I, 11, and III. In all known cases the two dimethylglyoxime anions lie in an essentially planar arrangement around each rhodium atom, whether the complex is dimeric rhodium(II),6 or monomeric rhodium(111).~7~ Very little information concerning kinetic or mechanistic studies of these complexes is available, although data on complexes containing other ligands are available.The compound H[Rh(DH),ClJ (A; DH, = dimethylglyoxime) more correctly formulated as [Rh(DH)-(DH,)Cl,] (although H,O+[Rh(DH),ClJ-is believed to be formed in water}, in suspension or neutral solution (containing the ion [Rh(DH),C1,]-},3y8 is reduced by the tetrahydroborate ion to rhodium(1). In solutions containing more than 0.lM-sodium hydroxide, it is reported that reduction occurs without the addition of tetrahydroborate ions. Whilst our observations are in agreement with this report, we find that reaction proceeds as soon as
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