Trivalent Heavy Transition Metal Ions

Gold(III) complexes are quite labile. Tobe reports a stopped flow study of the kinetics of substitution reactions of MeOH in [Au(C6H5)(MeOH)Cl2] at temperatures up to 0 °C in methanol. For anionic reagents, Nu , complexation is via a solvento pathway. The trans effect order of Nu and Nu parallels that for reactions of [AuC ] , although the nucleophilic discrimination is lower than in other gold(III) complexes. The kinetics of replacement of a range of thiazoles, oxazoles, and substituted pyridines, L, from the square-planar complexes [AUCI3L] by Cl in 

MeOH/water and 0.1 HCIO4 have been measured. In keeping with the associative mode expected for these complexes, the results are interpreted in terms of the ability of the incoming ligand, L, to stabilize the five-coordinate transition state. 

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The guest cations hitherto examined cover broadly uni- to trivalent and inorganic to organic ions that include alkali, alkaline earth, heavy and transition metal ions, as well as (ar)alkyl ammonium and diazonium ions. As to the complex stoichiometry between cation and ligand, both 1 1 stoichiometric and 1 2 sandwich complexes are analyzed. The solvent systems employed also vary widely from protic and aprotic homogeneous phase to binary-phase solvent extraction. 

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