6170
+
ri~-[Co(en)~(NHR~)Br] 2+ OH-
+
Concluding Remarks. The advantages of coordinated nucleophiles to effect organic reactions appear to be several. They seem to be extraordinarily efficient (where NHRz = NH2CH2CH2Br,NHzCHzCH20H,or even though their basicity is reduced by a factor of at C2H4NH) are the same, kobsd = kB,[OH-1, and the least 106-108on coordination to Co(II1). In this way second-order rate constants (kBr) are similar, Table VII. Both sets of results are consistent with the S N ~ C B substitution rates are enhanced over the intermolecular process by at least a factor of lo4, and possibly by as mechanism proposed for basic hydrolysis of acido comuch as 1012.24Also the metal may function as a balt(II1) complexes. l 4 Also, hydrolysis of the bromo protecting group for sensitive areas in the coordinated monodentate ethanolamine complex in the presence molecule, and since the complex moiety is asymmetric of N3- ion leads to chelated ethanolamine, hydroxoit may direct the organic synthesis to give a stereospeethanolamine, and azidoethanolamine products, precific product. Recovery of the organic species is readily sumably by competition for the five-coordinate deachieved through reduction of Co(II1) to the labile protonated intermediate by the coordinated nucleophile, Co(I1) complex in acid solution. Coordinated OHwater, and N3-. While similar competitive charactercould also be useful for hydrolysis of ligands sensitive istics are shown during the hydrolysis of related comto base in regions other than the reacting site, since plexes," a novel feature in the present instance is the the rate of the intramolecular reaction is likely to be intervention of the coordinated nucleophile; this aspect independent of hydroxide ion at a p H >6. Finally, of the study may lead to some interesting synthetic the reactions discussed in this paper offer interesting possibilities and to a more sensitive way of looking possibilities for the synthesis of chelate complexes. For at competition during the base hydrolysis of cobaltexample, using a sufficiently acidic cis-amine group, (111) complexes. coordinated 2-bromoethylamine might be expected to All three cis-bromo complexes gave largely cis-hychelate rather than cyclize internally to ethylenimine. droxo or tris-chelate products in somewhat larger In this way stereoisomers of multidentate ligands might amounts (-86 %) then for the ci~-[Co(en)~NH~Br]~+ by stereospecifically synthesized. Similarly, nucleoanalog under the same conditions (77 %). Also partial philes other than N and 0 should also be effective. retention (-50 %) of optical activity was observed, which agrees with previous observations. However, Acknowledgments. One of us (C. E. D.) wishes to these aspects need to be examined more closely under thank the National Institutes of Health for a Research carefully controlled conditions, and the experiments Fellowship (1 F2 AM 37797-01) during the tenure of will be repeated in detail in connection with other which this work was carried out. Dr. J. McLeod of studies relating to the mechanism of the base hydrolysis this school is thanked for assistance in obtaining the reaction. MS 9 mass spectra.
+
[ C O ( ~ ~ ) ~ ( N H R ~ ) O HBr]~+
Equilibria and Rates in the Formation of [Ru(NH3)5N2]2+ and [ ( ~ u w " 5 ~ ) ,N,I ) 4+ J. N. Armor and H. Taube* Contribution from the Department of Chemistry, Stanford University, Stanford, California 94305. Received May 4, 1970
+
+
Abstract: The equilibrium constant KI for the reaction RU(NH&OH~~+Nz(aq) = Ru(NH&Nt2+ HzO(liq) has been measured both by a static and a kinetic method. K1at 25" is 3.3 X lo4,and AH1"and AS1" by the static and kinetic methods, respectively, are -10.1 rt 1.4, -9.4 + 0.9 kcal/mol and -13 += 5 , -10 i 3 eu. The equiN ~[ R ~U + (NH~)~N~R~(NH& HzO(1iq) ]~+ librium constant Kz for the reaction R U ( N H ~ ) ~ O H ~R~U+( N H ~ ) ~ = hasbeenmeasuredbyastaticmethod. At25"andp = O.lO,Kz= 7.3 x 103,AHz0= -11.2 k 1.4 kcal/mol, and is 7.3 x 10-2 M-l sec-I, in good ASz" = -20 =!= 5 eu. The rate constant kl for the formation of RU(NH~)~N,~+ agreement with published measurements, AHl* = 18.3 i 0.3 kcal/mol and A&* = -2 f 1 eu. For the aquation of Ru(NH&N22+,L1= 2.03 x 10-6 sec-' at 25.0", AH-1* = 27.7 0.8 kcal/mol, and AS-l* = 8 3 eu.
+
+
*
arlier experiments 1,2 showed R U ( N H ~ ) ~ N 3 , 4 ~and ~+ [(Ru(NH&)2N2l4+ t o be stable with respect to R u ( N H ~ ) ~ O Hand ~ ~N + z or [ R U ( N H ~ ) ~ N ~ ]Data ~ + . on the rates of formation of the two complexes have been * To whom correspondence should be addressed.
E
(1) D. E. Harrison and H. Taube, J . Amer. Chem. Soc., 89, 5706 (1967). (2) D. E. Harrison, E. Weissberger, and H. Taube, Science, 159, 320 (1968). (3) A. D. Allen and C. V. Senoff, Chem. Commun., 621 (1965). (4) J. Chatt and J. E. Fergusson, ibid., 126 (1968).
*
p ~ b l i s h e d ,and ~ a recent communication6 describes the results obtained in a calorimetric determination of AH" for the process ~RU(NH&OH~~+ + N2(aq) = [(Ru(NH~)&N~]~+ + 2H~O(liq) It has also been reported' that over a period of 6 hr ( 5 ) I. J. Itzkovitch and J. A. Page, Can. J . Chem., 46, 2743 (1968). (6) E. L. Farquhar, L.Rusnock, and S . J. Gill, J . Amer. Chem. Soc., 92, 416 (1970). (7) J. N. Armor and H. Taube, ibid., 92, 2560 (1970).
Journal of the American Chemical Society / 92:21 / October 21, 1970
6171
little, if any, exchange resulted between the coordinated nitrogen of R U ( N H & N ~ ~and + free nitrogen over the solution, All of the results mentioned have a bearing on the equilibrium constants for reactions 1 and 2, but
secure the stopcock and joint seals. The flasks were covered with black tape and were stored in constant-temperature baths (+0.1"). Because our ionic medium differed from that adopted by Itzkovitch and Page, we found it necessary, in using the dynamic method to determine the equilibrium constants, to repeat their measurements of the forward rates for reactions 1 and 2. Using low rutheR U ( N H ~ ) ~ O H ~Nt(aq) ~ + = Ru(NH&N2*+ f HzO (liq) (1) nium concentrations, initial rates as measured by the absorbance at 221 nm yield accurate and reproducible values of k l , with no sigR u ( N H ~ ) ~ O H P " +Ru(NH3)sNzZf = nificant interference by reaction 2. The rate of formation of [(Ru[Ru(NH3)sN2Ru(NHs)~14+ HzO(liq) (2) (NH3)8)PNP]4+ was measured by the method of Itzkovitch and Page, the quantitative data on the important properties of the using the reactants [ R U ( N H & N ~ ] ~and + [ R u ( N H & O H ~ ] ~at + equal concentrations. two systems are lacking. We report here the results of The reverse rate for reaction 1 was determined by two methods. our determinations of the equilibrium constants for reIn one, a solution of Ru(NH3)5Nt2+,prepared either by dissolving actions 1 and 2 (& and &), respectively, as a function the bromide salt or by generating the ion by the action of excess of the temperature. CrZ+on NzO in the presence of the aquo ion, was saturated with Ar. The flasks, protected from light and maintained at 25", were swept Experimental Section with Ar, and at intervals analyses for [ R u ( N H ~ ) ~ N [(Ru(NH3)& ~]~+, NzI4+, and [ R U ( N H ~ ) ~ O H were ~ ] ~ + made as already described. Distilled water, redistilled from alkaline permanganate, was The concentration of R U ( N H ~ ) ~ O Hlost ~ ~ in + the formation of used in all experiments, Ionic strength was maintained by using [ ( R U ( N H ~ ) ~ ) ~(
