Pentaammines substitution reactions

IS further extended by the replacement of X by other anionic or neutral ligands. The inertness of the compounds makes such substitution reactions slow (taking hours or days to attain equilibrium) and, being therefore amenable to examination by conventional analytical techniques, they have provided a continuing focus for kinetic studies. The forward (aquation) and backward (anation) reactions of the pentaammines ... 

Y. Harel, A. W. Adamson. Photocalorimetry. 4. Enthalpies of Substitution Reactions of Rhodium(III) and Iridium(lll) Pentaammine Halides and of Ruthenium(II) Hexaammine. J. Phys. Chem. 1986, 90, 6690-6693. 

The mechanism of this activation of the C-H bond is unknown although the reaction may proceed by an oxidative addition. Generally, the pentaammine-osmium(II) system is known to activate phenols, anilines, and anisoles toward electrophilic addition and substitution reactions by binding the aromatic ligand in an T -fashion. Protonation, for example, results in the formation of a heterotriene system [30b] ... 

Pentaammine(trifluoromethanesulfonato-0)iridium(III) trifluoromethanesul-fonate is a white powder that is air-stable provided it is not subjected to prolonged exposure to atmospheric moisture. The complex may be kept for many months in a desiccator over a suitable drying agent (silica gel, CaCL) without any noticeable decomposition. The aquation rate constant for the complex is 2.6 x 10 sec" at 25° (0.1 M CF3SO3H), and at elevated temperatures (60-80°) the rate of substitution is quite rapid in both aqueous and nonaqueous solvents. When dissolved in poorly coordinating solvents such as acetone or tetrahydrothiophene 1,1-dioxide (sulfolane), the solvent-substituted species are themselves comparatively labile, and many substitution reactions may be performed in these solvents. " ... 

For instance, as will be seen later in the text, there is general agreement that substitution reactions of pentaammine-Co " complexes follow mechanisms which are mostly 1 with a leaning towards D however, there is not the same agreement over the corresponding reactions of, say [Cr(NH3)5H20] for which I, borderline and Ij have all been proposed. The most recent evidence favours the latter. 

Complexes of trifluoromethanesulfonate anion with cobalt(III) are labile oward substitution under mild conditions, and they have proved to be useful synthetic precursors to a variety of aminecobalt(III) complexes. The pentaammine-(trifluoromethanesulfonato-O)rhodium(III) ion, which is readily prepared from [Rh(NH3)5Cl]Cl2 in hot CF3SO3H, is also versatile as a synthetic precursor. " Its synthesis and solvolysis to give essentially quantitative yields of the penta-ammineaqua- and hexaamminerhodium(III) ions are described below. The aqua complex has previously been prepared by the base hydrolysis or Ag -induced aquation of [Rh(NH3)5Cl]Cl2 in water, but the present method presents a cleaner and more rapid alternative. The methods for preparation of the [RhCNHj) ] ion have evolved from the procedure of J0rgensen. They involve prolonged reaction of [Rh(NH3)5Cl]Cl2 with ammonia in a pressure vessel at elevated temperature. The solvolysis of [Rh(NH3)5(0S02CF3)](CF3S0j)2 in liquid ammonia is a simple, high-yield, and rapid alternative. 

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