Aquation and Solvolysis

These reactions still provide many new references, which in the following pages are arranged partly by ligand type and partly by phenomenon probed. Arrangement is by relation of ideas rather than fully systematic. 

In a paper devoted to three aspects of substitution kinetics of [Co(amine)2(dien)Cl] cations, aquation is represented by the temperature dependence of rate constants for the unsym-fac-cis (28) and sym-fac-cis (29) isomers of the cations with amine = The cis-a isomer of [Co(trien)(imidH)Cl]  

An X-ray crystal structure of the complex [Co( q -tameH)(T -tame)Cl], where tame = l,l,l-tris(aminomethyl)ethane, has proved the presence of a bidentate tame ligand with one terminal nitrogen protonated (30). Equilibrium 

Substitution Reactions of Inert Metal Complexes—6 and Above 

As this is some 20 times faster than the aquation of 31, the nonobservation of 32 as an intermediate in the 31 to 33 reaction is understandable 

Recent kinetic studies have shown that the aquation of trans-[CoL(N02)C1] and trans-[C6LC 2 ] (L = a tetra-aza macrocycle) show large variations in rates. The dependence of the aquation rates on conformational strain energy only appears to apply to a limited number of compounds. The rate enhancements are best rationalized in terms of the ability of the macrocycle to fold toward the leaving group. These studies also show that very large rate enhancements in cobalt (III) complexes of 14-membered macrocycles only occur when w-dialkyl groups are present. 

The aquation kinetics of the chloropentaamminecobalt(III) ion in water-ethanol mixtures has been studied. The rate constants correlate well with the Grunwald-Winstein Y parameter and with the dielectric constant of the medium. The data supports a D mechanism for the reaction. The loss of chloride from the complexes cw-[Co(en)2(NH2CH2CH20H)Cl] and cw-[Co(en)2(NH2(CH2)3 0H)Cl] has been studied in aqueous ethyleneglycol at 40-65 °C in acidic media and at 20-35 °C in basic media.The rate constants decreased linearly with the increasing mole fraction of the cosolvent. The loss of chloride resulted in the formation of the chelated amino-alcohols as the main product. The observed solvent isotope effect (A h2oAd2o) = 112 at 50 °C, [HCIO4] =0.01 moldm for chloride release is lower than the value reported for the aquation of the cw-[Co(en)2(alkylamine)Cl] complexes (1.38-1.44). This result may indicate the lack of direct solvent intervention in the act of substitution at the cobalt(III) center, as expected for a true intramolecular reaction. 

The kinetics of aquation of cobalt(III) or iron(III) complexes having hydrophobic ligands are usually affected by the presence of sulfonate anions. This effect has been attributed to hydrophobic interactions between the complex cations and the sulfonate anions. A recent paper discusses electrostatic and hydrophobic interactions in ion association between a series of tripositive complex ions and sulfonate anions. Ion association constants were determined at 25 °C by means of conductivity measurements of aqueous mixed electrolyte solutions at an ionic strength of 0.01 mol dm Some specific interactions in addition to the electrostatic ones were found to play a role in the ion associations of S04 with [Co(NH3)6] and [Cr(en)3], in those of QHsSO and - 5114(803)2 with [Co(phen)3] and [Co(bipy)3] . 

The dichlorotetrakis(pyridine)cobalt(III) complex has received attention, at it undergoes hydrolysis at the same rate in acidic and basic media. This observation and the fact that the complex contains no acidic hydrogen atoms 

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