Solvolysis of Organic Ligands

Solvolysis of Organic Ligands.— The catalysis of hydrolysis of organic esters by metal ions or complexes has been much studied for many years. Recent examples of kinetic studies include hydrolysis of oxalate esters catalysed by a variety of ions, and of the bis[-L-(-J-)-histidine methyl ester] complexes of copper(n) and of nickel(n). The relative catalytic effects of several copper(n) complexes, including Cu(imda), Cu(nta), and Cu(dien) +, on the hydrolysis of methyl glycinate have been determined. Rate constants for base hydrolysis of this ester correlate with stability constants for mixed complexes of this ester with the above-named copper(n) complexes.  

The hydrolysis of glycinamide complexes of cobalt(m), viz. cis-[Co(en)2Br(glyNR R )] to give [Co(en)2(gly)] +, has been studied in alkaline solution by kinetic, stereochemical, and 0-labelling methods. The bromide ion is displaced first, and then comes cobalt-promoted hydrolysis 

The complex [Ru(NH3)5(NaO)] + is amongst the products of reaction of [Ru(NH8)6(NO)] with hydroxylamine, hydrazine, or ammonia. The nitrous oxide complex is thought to arise from nucleophilic attack at the co-ordinated nitrogen. This type of nucleophilic attack at the ligand is an exact parallel of attack by, for instance, azide or hydrazine at the carbonyl carbon of a metal carbonyl (see Part IV, Chapter 5). 

The hydrolysis of cyanato-complexes [MfNHalsfNCO)], where M = Ru or Rh, in acid solution produces [M(NH3)6l + and carbon dioxide. The rate law is, in dilute acid  

This simple second-order rate law is identical with that reported earlier for the hydrolysis of [Co(NHa)5(NCO)] +. At higher acid concentrations the rate law is more complicated since such intermediates as [Rh(NH8)5(NHaC02H)] +, which has been isolated, exist and have relatively long half-lives. The reaction mechanism suggested is reversible protonation of the cyanate nitrogen, followed by attack of water at the cyanate carbon, followed in turn by the liberation of carbon dioxide. 

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