419. Kinetics of the reaction of alkyl and aryl compounds of the nickel group with pyridine

Basolo, Fred; Chatt, J.; Gray, Harry B.; Pearson, Ralph G.; Shaw, B. L.

doi:10.1039/jr9610002207

Cited by 134 publications

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“…[18] Axial steric interactions have long been known to decrease the rate of substitution reactions of square-planar complexes. [19] For example, the rate of reaction of 2-picoline with…”

Section: Resultsmentioning

confidence: 99%

“…This hindrance has the effect of destabilising the expected trigonalbipyramidal transition state, an effect well-known in substitution reactions of square-planar Pt II complexes. [19] The pK a values of the monoaqua and diaqua adducts of both 1 and 2 are b 0.3 units lower than those similar cisplatin adducts. This, combined with slower hydrolysis (Table 3), is likely to result in a reduced intracellular activity of complex 1 compared to cisplatin and may contribute to its high activity against cisplatin-resistant cell lines.…”

Section: Discussionmentioning

confidence: 96%

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Stereospecific and Kinetic Control over the Hydrolysis of a Sterically Hindered Platinum Picoline Anticancer Complex

et al. 1998

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cis-[PtCl 2 (NH 3 )(2-picoline)] (1) (AMD 473) is a recently reported active anticancer complex. Hydrolysis may be an important step in its intracellular activation and interaction with DNA. In this paper we employed [ 1 H, 15 N] 2 D NMR spectroscopy to determine the hydrolysis rates for each chloride ligand of this complex and its 3-picoline analogue 2. We also report the pK a values of the aqua and diaqua ligands as well as the X-ray crystal structures of 1 and 2. For the 3-picoline complex 2 the rate of hydrolysis of the Cl À trans to NH 3 (k 1b 1.0 Â 10 À4 s À1, I 0.1m, 310 K) is similar to that of cisplatin, but slower for the Cl À trans to 3-picoline (k 1a 4.5 Â 10 À5 s À1 ). Both of the first hydrolysis rates for the 2-picoline complex 1 are slower than those of 2, but in contrast to 2, the hydrolysis of the Cl À trans to NH 3 (cis to 2-picoline) is slower (k 1b 2.2 Â 10 À5 s À1) than for the Cl À trans to 2-picoline (k 1a 3.2 Â 10 À5 s À1). The crystal structure of 2 revealed that the pyridine ring is tilted by 498 with respect to the Pt square plane, whereas in 1 the ring is almost perpendicular (1038). This introduces steric hindrance by the CH 3 group towards an axial approach to Pt from above, leading to a destabilisation of the expected trigonal-bipyramidal transition state, an effect well-known in substitution reactions of Pt II complexes. The pK a values for the monoaqua adducts of 1 (6.13 and 6.49) and 2 (5.98 and 6.26 for H 2 O trans to picoline and NH 3 , respectively) and for the diaqua adducts (5.22, 7.16 for 1 and 5.07, 6.94 for 2) are b 0.3 units lower than for cisplatin. The slowness of the hydrolysis, combined with the dominance of (inert) hydroxo species, is expected to contribute to a greatly reduced reactivity of the sterically-hindered 2-picoline complex under intracellular conditions.

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“…[18] Axial steric interactions have long been known to decrease the rate of substitution reactions of square-planar complexes. [19] For example, the rate of reaction of 2-picoline with…”

Section: Resultsmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 96%

Stereospecific and Kinetic Control over the Hydrolysis of a Sterically Hindered Platinum Picoline Anticancer Complex

et al. 1998

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“…First, the viscosity does not increase upon the addition of the same quantity of monomeric The faster dynamics in cross-linker 1 a provide a mechanism by which to evaluate the dynamic contributions of ligand exchange to the properties of the network. The thermodynamics and kinetics in 1-PVP are reported reliably by model system 2-3 ( Figure 2; not accounting for cooperativity, the effects of which we assume to be equivalent in all systems), [10,11] and NMR spectroscopy measurements on 2 a-3 and 2 b-3 reveal nearly identical association constants of 35 m À1 (2 a-3) and 29…”

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confidence: 84%

Strong Means Slow: Dynamic Contributions to the Bulk Mechanical Properties of Supramolecular Networks

2005

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The desire to control rationally, through small-molecule synthesis, the properties of bulk materials has led to supramolecular approaches to, for example, polymers, [1,2] strong and weak organogels, [3] amphiphilic assemblies, [4] and liquid crystals.[5] In these materials, specific and well-defined interactions between molecules contribute to bulk material properties on two levels: structure and dynamics. Although the dynamic nature of the defining interactions is often the attribute that distinguishes supramolecular materials from their covalent counterparts, [6] direct mechanistic studies of the molecular contributions to the dynamic properties of materials are less abundant than structural studies.[7] Herein, we report that a simple structural variation in the networks of supramolecular sols and organogels provides a direct and quantitative measure of the relationship between molecular dynamics and macroscopic rheological properties. The approach is akin to a macromolecular "kinetic isotope effect", in that kinetic contributions to rate-determining processes are revealed by the differences in two isostructural systems. We find that it is the dynamics of molecular crosslinks, much more so than their thermodynamics, which are specifically and quantitatively responsible for the bulk viscoelastic properties of the supramolecular networks.The system under consideration is poly(4-vinylpyridine) (PVP) that is cross-linked by bis(M ii -pincer) compounds 1 (see Figure 2) derived from the work of van Koten [8] (M = Pd or Pt, Figure 1). [9] We recently reported that simple steric effects in the alkylamino ligands of 1 and related compounds change the rate of ligand exchange by approximately two orders of magnitude while leaving the thermodynamics of association effectively constant. [10] This independent control of dynamics is particularly significant; cross-linkers 1 a and 1 b (Figure 2) are structurally identical components within the network, and so their similar thermodynamics ensure that the extent and nature of cross-linking is essentially the same in the samples prepared from them. By extending the family of cross-linkers to the Pt II -pincer molecules 1 c and 1 d (Figure 2) we are able to probe the effect of a wide range of molecular dynamics.The addition of 2 % (by functional group) 1 b to a 100 mg mL À1 DMSO solution of PVP (Aldrich, M r = 60 000) gives rise to a clear, thick, deep yellow solution whose viscosity is approximately 2000-times greater than that of PVP alone (33 Pa s vs. 0.016 Pa s). Two control experiments confirm that the viscosity increase is due to coordinative cross-linking of the PVP by 1 b. First, the viscosity does not increase upon the addition of the same quantity of monomeric À .

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“…alkyl, aryl) are among the strongest σ-donors and have a large kinetic trans effect; i.e., they increase the rate of substitution of a trans-positioned group. 5 Substitution reactions of Pt(II) complexes containing a single metalcarbon bond were first investigated more than 30 years ago, 7 and later studies with complexes containing two, [8][9][10] three, 11 and four 12,13 metal-carbon bonds have shown interesting kinetic and mechanistic features.…”

Section: Introductionmentioning

confidence: 99%

Comparative Rates of Ligand Substitution Reactions of Pt−C-Bonded Complexes in Aqueous Solution and the X-ray Crystal Structure of [Pt{C₆H₃(CH₂NMe₂)₂-2,6}(OH₂)][OSO₂CF₃]

et al. 1996

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The substitution behavior of the organometallic complex cation [Pt{C 6 H 3 (CH 2 NMe 2 ) 2 -2,6}-(OH 2 )] + (1) has been studied with a series of nucleophiles (Cl -, Br -, I -, N 3 -, NCS -, thiourea, N, N′-dimethylthiourea, N,N,N′N′-tetramethylthiourea) as a function of nucleophile concentration ([Nu]), pH, temperature, and pressure. Complex 1 affords pseudo-first-order rate constants, k obs , for the complex-formation reaction given by k obs ) k 1 [Nu] + k -1 ; the k -1 term is due to the reverse aquation reaction and is insignificant for the stronger, S-donor nucleophiles. The mechanism for the substitution of the coordinated water molecule is associative, as demonstrated by the large negative values of ∆S q and ∆V q . The results are compared to those obtained earlier for the geometrically related neutral zwitterionic complex [Pt{C 6 H 4 (CH 2 NMe 2 )-2}(NC 5 H 4 SO 3 -3)(OH 2 )] (2). Both cyclometalated complexes 1 and 2 have very high substitution reactivities that can be ascribed to labilization which arises from the σ-bonded carbon atom of the ortho-metalated aryl ligand in combination with back-bonding to the in-plane aryl ligand that increases the electrophilic character of the Pt(II) center. In complex 1 the σ-donicity of the second chelating dimethylamine group and/or the increased chelation effect of the tridentate ligand lead to a significantly increased lability of the coordinated water molecule, compared to complex 2. The X-ray structure of the ionic complex [Pt{C 6 H 3 (CH 2 NMe 2 ) 2 -2,6}(OH 2 )] + [OSO 2 CF 3 ] -(1a) is described. The crystal structure comprises an aggregate of two complex cations and two triflate anions. The structure contains two fully equivalent square-planar coordinated Pt(II) centers with an O-ligated neutral H 2 O molecule (Pt-O ) 2.186 (2) Å) trans to the Pt-C aryl bond (Pt-C ) 1.903(2) Å); the aggregate results from the involvement of both H atoms of the two H 2 O molecules in asymmetric hydrogen bonding to O atoms of the two triflate anions.

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419. Kinetics of the reaction of alkyl and aryl compounds of the nickel group with pyridine

Cited by 134 publications

References 0 publications

Stereospecific and Kinetic Control over the Hydrolysis of a Sterically Hindered Platinum Picoline Anticancer Complex

Stereospecific and Kinetic Control over the Hydrolysis of a Sterically Hindered Platinum Picoline Anticancer Complex

Strong Means Slow: Dynamic Contributions to the Bulk Mechanical Properties of Supramolecular Networks

Comparative Rates of Ligand Substitution Reactions of Pt−C-Bonded Complexes in Aqueous Solution and the X-ray Crystal Structure of [Pt{C₆H₃(CH₂NMe₂)₂-2,6}(OH₂)][OSO₂CF₃]

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419. Kinetics of the reaction of alkyl and aryl compounds of the nickel group with pyridine

Cited by 134 publications

References 0 publications

Stereospecific and Kinetic Control over the Hydrolysis of a Sterically Hindered Platinum Picoline Anticancer Complex

Stereospecific and Kinetic Control over the Hydrolysis of a Sterically Hindered Platinum Picoline Anticancer Complex

Strong Means Slow: Dynamic Contributions to the Bulk Mechanical Properties of Supramolecular Networks

Comparative Rates of Ligand Substitution Reactions of Pt−C-Bonded Complexes in Aqueous Solution and the X-ray Crystal Structure of [Pt{C6H3(CH2NMe2)2-2,6}(OH2)][OSO2CF3]

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Comparative Rates of Ligand Substitution Reactions of Pt−C-Bonded Complexes in Aqueous Solution and the X-ray Crystal Structure of [Pt{C₆H₃(CH₂NMe₂)₂-2,6}(OH₂)][OSO₂CF₃]