The four new complexes of the mixed cyanoammine and -diamine series cis-and írares-Co(CN)2(NH3)4+, i;'a»s-Co(CN)2(en)2+, and »er-Co(CN)sdien were prepared and characterized by visible and ultraviolet absorption spectra as well as infrared spectra.In addition, the known complexes, ?»er-Co(CN)3(NH3)3, m-Co(CN)2(en)2+, and Co CN(NH3)52 + have also been prepared. All of these complexes were synthesized by the reaction of potassium cyanide with Co(NH3)e3+, Co(en)33+, or Co-(dien)23 + in the presence of activated charcoal at low temperature (0-5°).
Experimental SectionPreparation. (1) dx-Dicyanotetraamminecobalt (III) Chloride Monohydrate, fro?zi-Dicyanotetraamminecobalt(III) Chloride, and mer-Tricyanotriamminecobalt(III):cis-[Co(CN)2-(NH3)4]C1-H20, trans-[Co (CN )2(NH3)4] Cl, and 4»er-Co(CN)"-(NH3)3.-To a cold solution (ca. 0°) of 17 g (0.05 mol) of [Co-(NH3)6](02CCH3)3 in 200 ml of water, 10 g (0.15 mol) of potassium cyanide in 50 ml of cold water was added dropwise with stirring. Two grams of activated charcoal was added to the above solution, and the mixture was kept in a refrigerator for 1 week without stirring (or 3-4 days with stirring). After that, the reaction mixture was filtered, and the filtrate was diluted to 600 ml with water.About 150 ml of this solution was poured into a(1) P.
Optical inversion of coordinated 2-methyl-2-butene and trans-2-butene in trans(N)-chloro-l-prolinato-olefinplatinum(II), trans(N)-[PtCl(l-prol)(olefin)] (nitrogen of l-prolinate ion is trans to the olefin), i.e. the interconversion between diastereoisomers (Fig. 1), has been kinetically studied in acetone by measuring the decrease in the intensity of circular dichroism (CD) in near ultraviolet region. The rate was measurable only in the presence of olefin, and can be expressed by the relation, Rate=k[complex][olefin]. The Ea and the ΔS\eweq values for the two complexes are 7.8±1.0 and 9.0±1.0 kcal/mol, and −44 and −39 entropy unit, respectively. The coordinated trans-2-butene is replaced by other olefins, 2,3-dimethyl-2-butene, 2-methyl-2-butene, trans-2-butene (optical inversion), and styrene, under similar conditions to give the same rate formula. The second order rate constant increases in the given order. The inversion seems to take place via bimolecular mechanism with excessive olefin as nucleophile. The corresponding complexes containing styrene and its para derivatives give such an inversion much faster in the absence of excess of olefin. With change of para substituents, the rate increases in the order, methoxy<methyl<hydrogen<chloro<nitro. This seems to be related with their electrondrawing ability.
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