Base Hydrolysis of Pentaaminecobalt(III) Complexes: The [CoX(dien) (dapo)]ⁿ⁺ system. Part 2. Structure and reactivity of the pentacoordinate intermediate

Abstract

Base hydrolysis of optically pure mer-exo(H)-and mer-endo (H)-[CoCl(dien)(dapo)]*+ (A and B (X = CI), resp.; dien = N-(2-aminoethyl)ethane-1,2-diamine; dapo = 1,3-diaminopropan-2-01, koH = (1.13 i 0.09). 10' (A (X = CI)), koH = (1.18 * 0.1 I ) . 105~vr1s-l (B (X = Cl)); I = 1 . 0~ (NdC1O4 or NaN,), T = 298 K) is

Base Hydrolysis of Pentaaminecobalt(III) Complexes: The [CoX(dien) (dapo)]n+ system. Part 1. Syntheses, structures, configuration, and spectroscopy

“…that the reasons given in 141 for the high reactivity of the structurally similar rner-[CoX(dien)(tn)l"+ ion might not be generally applicable, and that they might only be coincidental with our results [5]. [7] and of the mer-exo(H)-and mer-endo(H)hydroxo and -aqua complexes A and B (X = OH and H,O, resp. ), respectively, [8] is given in the following papers.…”

“…Essentially the same procedure was used to produce A(CIO,), (X = Cl) from the unsym-Sac-endo (OH)-isomer D. However, the initial base-hydrolysis step is much faster [7], and a reaction time of 1 min was sufficient. The final yield ofA(CIO,), (X = CI) was low (ca.…”

“…The mer-endo(H)-[CoCl(dien)(dapo)]'+ (B, X = Cl) species may be isolated in very small amounts from the above reaction mixture. However, B (X = Cl) is more conveniently prepared from the corresponding azido complex B (X = N,) which results from anation of the mer-hydroxo complex or which arises from azide competition during base hydrolysis: 7:3 mixtures of the mer -exo-(H)-and mer-endo (H)-epimers A and B (X = NJ, respectively, are obtained in either case, and were readily separated [7]. The yield of complex D (X = Cl) from the oxygenation reaction is also quite poor, but D (X = Cl) is prepared in relatively high yield by direct cleavage of the superoxido precursor after first reducing it to the peroxo ion with I-.…”

Kinetics and Mechanism of Base Hydrolysis in Cobalt(III) Complexes – The Case of a Complex CoLCl2+ where L has the Novel Topology of a Square-Pyramidal NN4 Coordination Cap

“…Still, base hydrolysis is practically as necessarily so. [12,23] It was therefore repeatedly concluded slow as in the case of 2. This may suggest that the rate at that the differences in the rate of base hydrolysis are mainly which cobalt(III) complexes of the type Co'N 5 'Cl 2ϩ follow governed by the lability of the conjugate base rather than the D cb mechanism will also be affected by the symmetry by differences in proton labilities of the parent complex.…”

“…[20] The observed ratio for k OH (I ϭ 0.1 )/k OH (I ϭ 1.0 ) ϭ 2.4 is in accord with the averaged value k OH (I ϭ balt(III) complexes. [9] It has been shown that anion competition experiments [22,23] and the determination of reaction volume profiles [24] can provide experimental evidence for the validity of the commonly accepted D cb mechanism. In order to substantiate the operation of the D cb mechanism for the base hydrolysis of 2, experiments at different temperatures (see Table 4) and pressures (see Figure 5) were carried out.…”