Ligand Substitution Reactions in Aqueous Solution

substitution is a simple process of one type of ligand being replaced fully by another type of ligand, such as for reaction of [V(0H2)6](S04) in (6.2). 

However, the outcome of such reactions does depend on the entering ligand, as the above reaction performed with the aromatic monodentate amine pyridine instead of 1,2-ethanediamine leads to only four pyridines binding, with [V(py)4(S04)] as the product. 

Substitution with change in coordination number may also occur in some cases. A clear example of this occurs for Ni2+aq reacting with pyridine, which undergoes the process (6.3). 

Complex formation is but the first stage of synthesis, as it is usually true that we require the product in a solid form, isolated as a salt or neutral compound. There are a number of approaches to the isolation of a solid  

As an example of the value of anion exchange reactions, the product from reaction of Ni(S04) with pyridine in water, the complex cation [Ni(py)4](S04), is highly soluble. However, addition of excess sodium nitrite leads to ready precipitation of the much less soluble [Ni(py)4](N02)2 complex change of the counter ion alone has occurred (6.4). 

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Ligand-substitution reactions in aqueous solutions rarely proceed directly. Instead, the leaving ligand is first replaced by H2O, which is present in aqueous solution at a concentration of 55 M, the entering ligand then substitutes the metal-bound H2O (M-OH2) inthe so-called anationreaction. Therefore, the rate constant of forward reactions, which could be considered as the reactivity of aquo-metal species, will parallel the order of water substitution in the inner coordination sphere of the corresponding metal ions Cs > Ba > Hg2+ > K+ > Cr2+ Cu + > Na+ > Sr + Li+ > Ca + > Cd + > Mn2+ Zn + > Fe + > Co + > Mg + > nP+ > Pd + > Pt + > cases, the interactions between... 

Rate and Equiubriijm Constant Data for Axial Ligand Substitution Reactions in Aqueous Solutions... 

THE APPLICATION OF A DYE-LASER PHOTOCHEMICAL RELAXATION TECHNIQUE TO THE STUDY OF METAL-LIGAND SUBSTITUTION REACTIONS IN AQUEOUS AND MICELLAR SOLUTIONS... 

The process we are seeing in the copper(II)-ammonia solution is a ligand substitution process, where one ligand is replacing another. In general, we can represent this, for reaction in aqueous solution with a neutral monodentate ligand at this stage, by Equation (5.1) ... 

Ligand field irradiation of chromium(III) complexes leads primarily to substitution reactions/ The most common reaction in aqueous solution is photosubstitution of a ligand by water. One of the earliest studies of photoaquation reactions was the light-induced exchange of water between Cr(H20) and the solvent. The reaction is followed by using isotopically labeled H2O as the solvent, where sequential photosubstitution of the H2O molecules leads to the formation of Cr(H20 )6 (Ref.3) ... 

The diazonium salts 145 are another source of arylpalladium com-plexes[114]. They are the most reactive source of arylpalladium species and the reaction can be carried out at room temperature. In addition, they can be used for alkene insertion in the absence of a phosphine ligand using Pd2(dba)3 as a catalyst. This reaction consists of the indirect substitution reaction of an aromatic nitro group with an alkene. The use of diazonium salts is more convenient and synthetically useful than the use of aryl halides, because many aryl halides are prepared from diazonium salts. Diazotization of the aniline derivative 146 in aqueous solution and subsequent insertion of acrylate catalyzed by Pd(OAc)2 by the addition of MeOH are carried out as a one-pot reaction, affording the cinnamate 147 in good yield[115]. The A-nitroso-jV-arylacetamide 148 is prepared from acetanilides and used as another precursor of arylpalladium intermediate. It is more reactive than aryl iodides and bromides and reacts with alkenes at 40 °C without addition of a phosphine ligandfl 16]. 

The coupling of Naphtol AS or its phenyl-substituted derivatives with diazonium salts from variously substituted anilines in aqueous alkaline solution (section 4-11) gave incomplete reactions and impure products in some instances, probably because these coupling components have inadequate solubility in aqueous media. Pure dyes in ca. 90% yields were obtained by reaction in dimethylformamide in the presence of sodium acetate. Metallisation of these o,o -dihydroxyazo ligands with sodium chromium salicylate or a cobalt(II) salt gave metal-complex dyes in 80-100% yields [22]. Specific structural isomers of these complexes were identified by i.r., n.m.r., Raman and UV/visible spectroscopy [23]. 

A Co(IH) complex is inert in ligand-substitution reactions, and its uniform structure is thus maintained even in an aqueous solution. The reaction mechanism of a Co(III) complex in solution is well known, so that a pendant-type polymer-Co(IU) complex, e.g. 17,19, is one of the most suitable compounds for a quantitative study of the effects of a polymer ligand on the reactivity of a metal complex. The reactivities of the polymer-Co(III) complexes are discussed here kinetically and compared with those of the monomeric Co(III) complexes in the following reactions electron-transfer reactions between the polymer complexes and Fe(II) [Eqs. (5) and (6)], and the ligand-substitution reaction of the polymer-Co(III) complex with hydroxy ions or water [Eqs. (7) and (8)J. One of the electron-transfer reactions proceeds via... 

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