The Effect of Chelation and of Alkyl Substitution on the Rate of Hydrogen Exchange in Cobalt(III) Ammines

Basolo, Fred; Palmer, Jay; Pearson, Ralph G.

doi:10.1021/ja01490a015

Cited by 22 publications

(5 citation statements)

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“…Confirmation of this mechanism is afforded by the fact that the kinetic characteristics of the base-catalyzed oxalate exchange (studied by means of C^O,2-) and of the spectrophotometrically observed decomposition reaction are identical with those of the "racemization." The contrast between the behavior of Coen2C204+ and that of the trisoxalato complex may possibly be ascribed to the existence of strong N-H-0 hydrogen bonding in the former, as suggested in recent deuterium-exchange studies (38,51,250).…”

mentioning

confidence: 82%

The Chemistry of the Metal Oxalato Complexes.

Krishnamurty¹,

Harris²

1961

Chem. Rev.

185

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mentioning

confidence: 82%

The Chemistry of the Metal Oxalato Complexes.

Krishnamurty¹,

Harris²

1961

Chem. Rev.

185

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“…Surprisingly, little work has been directed at how the reactivity of transition metal complexes containing chelating or non-chelating ligands differ. It would appear that not since Basolo et al [23] first commented on the influence of chelation on substitution reactions in their studies on the rate of hydrogen exchange in cobalt(III) amines, finding that the rate of hydrogen exchange does increase with an increase in chelation, has any work been done on elucidating the role of chelation on the substitution behaviour of transition metal complexes.…”

Section: Introductionmentioning

confidence: 99%

Does increased chelation enhance the rate of ligand substitution at PtII (N,N,N) centres? A detailed kinetic & mechanistic study

Reddy

Jaganyi

2006

Transition Met Chem

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The rate of substitution of the chloride and aqua moieties from the platinum(II)-amine complexes, viz. [Pt(dien)Cl]Cl (Pt1-Chloro) and [Pt(en)(NH 3 )Cl]Cl (Pt2-Chloro) and their corresponding aqua analogues, viz. [Pt(dien)(OH 2 )] (ClO 4 ) 2 (Pt1-Aqua) and [Pt(en)(NH 3 )(OH 2 )](ClO 4 ) 2 (Pt2-Aqua), by a series of neutral and anionic nucleophiles,viz. thiourea (TU), 1,3-dimethyl-2-thiourea (DMTU), 1,1,3,3-tetramethyl-2-thiourea (TMTU), iodide (I ) ) and thiocyanate (SCN ) ), was determined under pseudo first-order conditions as a function of concentration and temperature using UV/Visible spectrophotometry and standard stopped-flow techniques. The observed pseudo first-order rate constants for the substitution reactions obeyed the simple rate law k obs =k 2 [Nucleophile]. Second-order kinetics and negative activation entropies, ca. )93 J K )1 mol )1 and )71 J K )1 mol )1 , for the chloro and aqua complexes respectively, support an associative mode of activation. The rate of substitution of both the chloro and aqua moieties are observed to decrease with an increase in the steric bulk of the neutral nucleophiles, whilst rate of substitution by SCN ) was observed to be faster than that of I ) , in correlation with the observed nucleophilicities of the two nucleophiles. A comparison of the second-order rate constants, k 2 , at 298 K, obtained for the substitution reactions of Pt1 and Pt2 shows that an increase in chelation in moving from Pt2 to Pt1 results in a corresponding increase in the reactivity, by a factor of ca. 3, (28.31±0.15 and 8.02±0.13 M )1 s )1 for Pt1 and Pt2 respectively, in the case of substitution of the aqua species by TU). Computational analysis of the chloro complexes, viz. Pt1-Chloro, Pt2-Chloro and [Pt(NH 3 ) 3 Cl]Cl (Pt3) support this conclusion by demonstrating that the Pt-N bond trans to the leaving group is shortened and that the Pt-Cl bond is lengthened when chelation is increased from Pt3 to Pt1. Consequently, these results suggest that the increase in reactivity of Pt1 over Pt2, promoted by increased chelation, is as a result of ground state destabilization.

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“…Contributions to 59Co Relaxation at pH 5.9 K. D. Rose and R. G. Bryant termined independently of the NH protons in the chelate complexes by studying the 59Co relaxation in D20 as well as H20 since the nitrogen protons are readily exchanged for deuterons. 27 Direct confirmation of the cobalt-nitrogen coupling could be achieved by observation of the 14N-decoupled 59Co spectrum. The effectiveness of the nitrogen coupling to the cobalt relaxation may be determined directly also by taking advantage of the well-known inverse-temperature and viscosity dependence for the line width of a nucleus that is relaxed by a scalar interaction of the second kind.…”

Section: Resultsmentioning

confidence: 99%