Pentaammines 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 ... 

Cobalt, hexaamminetrifluoroacetato-photothermography, 6,119 Cobalt, nitropentaammine-, 1, 3 Cobalt, octacarbonyldi-exchange reactions, 1,289 Cobalt, pentaammine-electron transfer, 1, 373... 

Utilizing an alternate mode of Diels-Alder reactivity, Harman has examined the cycloaddition reactions of 4,5-T -Os(II)pentaammine-3-vinylpyrrole complexes with suitably activated dienophiles <96JA7117>. For instance, cycloaddition of the p-vinylpyrrole complex 58 with 4-cyclopentene-l,3-dione, followed by DDQ oxidation affords 59, possessing the fused-ring indole skeleton of the marine cytotoxic agent, herbindole B. 

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. 

Diverse lines of evidence support the conclusion that a chemical mechanism is operative in certain reactions of the type under consideration. In certain systems this evidence is quite direct.160 Thus, when Cr2+ reacts with pentaammine-0-(pyrazinecarbonylato)cobalt(III), the first very rapid reaction phase (k > 106 M-1 s-1) leads to a green intermediate which in a slower first-order process (k = 4.5 x 102 s-1) produces Co2+(aq) and a Cr111 chelate of the new ligand. ESR measurements on the reaction mixture in a rapid flow apparatus show that the green intermediate is a radical cation.161... 

SCN-, or F ) has been studied using acidic perchlorate media. The rhodo ion yields Cr(NH3)5(H20)3 +, whereas the erythro ions yield both Cr(NH3)5(H20)3+ and the respective cis or trans isomers of Cr(NH3)4(H20)X(3 M,+. The kinetic data are consistent with a contribution from the uncatalyzed path (k0 in Scheme 3) alone, and yield the parameter values listed in Table XXV. Bond rupture in the unsymmetric species is assumed to occur at the Cr(NH3)4X fragment, since, when trans chloroerythro is cleaved in the presence of Cl- or Br, the halide is incorporated into the tetraammine fragment while the pentaammine fragment remains as Cr(NH3)5(H20)3+ (252). The cleavage of the cis aquaerythro ion in the presence of Cl- and Br-, respectively, has been studied (254), and both systems follow the rate law — d[dinuclear]/d< = (kx + A2[X])[dinuclear], where X = Cl- or Br-. In the reaction with chloride the products are Cr(NH3)5(H20)3 + and cis-Cr(NH3)4Cl(H20)2 +, and the formation of cis chloroerythro as an active intermediate was proposed. In contrast to this, the products in the bromide reaction are Cr(NH3)5(H20)3+ and cis-Cr(NH3)4(H20)23+. The enhancement of the cleavage rate by bromide has been explained in terms of ion-pair formation. 

Solutions of pentaammine(nitrogen)ruthenium(II) have been prepared from ruthenium (III) chloride and hydrazine hydrate.1,2 These solutions have been used to prepare pentaammine-haloruthenium(III) salts [Ru(NH3)6X]X2 (X = Cl, Br, I). [Ru(NH3)5C1]C12 has been converted to pure pentaammine-(nitrogen)ruthenium(II) salts—[Ru(NH3)5N2]X2 (X- = Cl-, Br-, I-, BF4-, PFg-)—via the reaction between azide ion and aquopentaammineruthenium(III).2 Hexaammineruthe-nium(III) salts—rRu(NH8)6]X3 (X = I-, BF4-)—have been prepared by the reaction between pentaamminechlororuthenium-(III) chloride and hydrazine monohydrochloride. 

Prepared as described in reference 3, and recrystallized from dilute HC10 three times as discussed in reference 1. An equivalent amount of [Co(NH ) C1]C12 which has been allowed to aquate for 4 days at room temperature can be used, but lower yields are obtained. The purity of the initial pentaammine complex is important. Hexaammine impurities are carried through the reaction sequence. 

Reaction of [Ru(L)2(bipy)2]2+ with [Ru(NH3)5OH2]2+ in the dark in acetone yields the [2,2,2]6+ trimer [(H3N)5RuIILRuII(bipy)2LRuII(NH3)5]6+ (L = pz, 4,4 -bipy, l,2-bis(4-pyridyl)ethylene, 1,2-bis(4-pyridyl)ethane) 567 oxidation with Br2 to give the [2,2,3]7+ and [3,2,3]s+ systems was achieved. The sites of oxidation appear to be localized, with no long range interaction between remote pentaammine moieties.567... 

A S oh = + 38 + 6JK mol .5SS For both the spontaneous and base-catalyzed paths, the rates of isomerization for the three pentaammines follow the order Rh > Co > Ir for the base-catalyzed path the reaction rates are of the order 278 217 1, while for the spontaneous path (ks), the relative rate constants are 32 2.3 1. The greater reactivity of the Rh complex, attributed to a lower AH for both the spontaneous and base-catalyzed paths, contrasts sharply with the order generally observed for the aquation of d6 pentaammines. For example, for M = Co, Rh and Ir, the aquation of [M(NFI3)5Br]2+ in acidic solution occurs with relative rate constants of 4 1 0.001.587 The ordering is not always Co > Rh P Ir, however, as the rates of water exchange in aquapentaammine complexes in the Rh triad have relative rates of 0.53 1 0.0059,559 and the relative rates of acid aquation of the [M(NH3)5(C03)r ions are 1 1 0.02.518... 

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