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Structure-Reactivity Correlations for Complex Formation Reactions between Square-Planar Metal Centers and Thioethers

Shi, Tiesheng LU and Elding, Lars Ivar LU (1996) In Inorganic Chemistry 35(20). p.5941-5947
Abstract (Swedish)
Synopsis
Reactivity trends of thioethers toward square-planar complexes can be generally interpreted by use of an equation of the form:  log k = γ + α∑σ* + βθ, where k denotes second-order rate constants, ∑σ* the sum of Taft constants for the thioether substituents, and θ the thioether cone angles. γ represents an intrinsic parameter for each substrate complex, while α is an electronic and β a steric parameter. Large variations in both electronic and steric properties of the entering ligands indicate that there is no duality behavior in the reactions of thioethers with square-planar metal centers.
Abstract
Abstract Image
Kinetics for complex formation between Pd(H2O)42+ and thioethers of largely varying electronic and... (More)
Synopsis
Reactivity trends of thioethers toward square-planar complexes can be generally interpreted by use of an equation of the form:  log k = γ + α∑σ* + βθ, where k denotes second-order rate constants, ∑σ* the sum of Taft constants for the thioether substituents, and θ the thioether cone angles. γ represents an intrinsic parameter for each substrate complex, while α is an electronic and β a steric parameter. Large variations in both electronic and steric properties of the entering ligands indicate that there is no duality behavior in the reactions of thioethers with square-planar metal centers.
Abstract
Abstract Image
Kinetics for complex formation between Pd(H2O)42+ and thioethers of largely varying electronic and steric properties, viz. MeSCH2COOH, (n-Pr)2S, EtSCH2CH2OH, S(CH2CH2CH2OH)2, S(CH2CH2OH)2, EtSCH2COOH, S(CH2COOH)2, S(CH2CH2COOH)2, (i-Pr)2S, (s-Bu)2S, (t-Bu)2S, and protonated thiomorpholine, S(C2H4)2NH2+, has been studied by use of stopped-flow spectrophotometry in an acidic aqueous medium. Second-order rate constants k1298 are 1.61 × 104, 8.0 × 104, 3.79 × 104, 3.69 × 104, 2.21 × 104, 1.84 × 104, 1.91 × 103, 1.34 × 104, 1.52 × 104, 7.75 × 103, 900, and 5.2 × 103 M-1 s-1, respectively. The reactivity toward Pd(H2O)42+ of all thioethers studied so far can be described as a function of their σ-donor properties as expressed by the sum of the Taft constants, ∑σ*, and their steric requirements as defined by cone angles, θ, by use of the equation:  log k1 = (9.9 ± 0.3) − (0.67 ± 0.05)∑σ* − (0.059 ± 0.003)θ. Similarly, second-order rate constants k298 reported previously for reactions between thioethers and Pd(dien)H2O2+ and Pt(dien)Br+ are described by log k298 = (10.5 ± 0.6) − 0.67∑σ* − (0.081 ± 0.006)θ and log k298 = (4.6 ± 0.6) − 0.72∑σ* − (0.080 ± 0.006)θ, respectively. Hence, the reactivity trends of thioethers toward square-planar complexes can be given a general interpretation in terms of intrinsic, electronic, and steric parameters, by use of log k = γ + α∑σ* + βθ. Large variations in both electronic and steric properties of the entering ligands indicate that there is no “duality behavior” in the reactions of thioethers with square-planar metal centers, as claimed in previous literature. No steric threshold is observed for these sterically unhindered systems. There is a rough compensation effect between ΔH1⧧ and ΔS1⧧, i.e. a smaller ΔH1⧧ is usually accompanied by a larger negative ΔS1⧧, indicating that all thioethers react via the same mechanism. It appears that the much lower reactivity observed for the highly branched (t-Bu)2S is primarily caused by a high activation enthalpy. Volumes of activation have been determined for a series of thioethers with a constant cone angle, viz. EtSCH2COOH, S(CH2COOH)2, and S(CH2CH2COOH)2 through high-pressure stopped-flow measurements. Values of ΔV1⧧ are −7.9 ± 0.5, −8.1 ± 0.4, and −7.6 ± 0.3 cm3 mol-1, respectively. These values together with that for Et2S (−8.7 ± 0.1 cm3 mol-1) determined previously shows that variation of electronic properties, steric factors being kept constant, change the reactivity markedly, but have no observable influence on the activation volumes. Stability constants β1 for five palladium thioether complexes derived as the ratio between rate constants for forward and reverse reactions vary between (1.2 ± 0.3) × 104 and (3.2 ± 0.7) × 104 M-1. (Less)
Abstract
Synopsis
Reactivity trends of thioethers toward square-planar complexes can be generally interpreted by use of an equation of the form:  log k = γ + α∑σ* + βθ, where k denotes second-order rate constants, ∑σ* the sum of Taft constants for the thioether substituents, and θ the thioether cone angles. γ represents an intrinsic parameter for each substrate complex, while α is an electronic and β a steric parameter. Large variations in both electronic and steric properties of the entering ligands indicate that there is no duality behavior in the reactions of thioethers with square-planar metal centers.
Abstract
Abstract Image
Kinetics for complex formation between Pd(H2O)42+ and thioethers of largely varying electronic and... (More)
Synopsis
Reactivity trends of thioethers toward square-planar complexes can be generally interpreted by use of an equation of the form:  log k = γ + α∑σ* + βθ, where k denotes second-order rate constants, ∑σ* the sum of Taft constants for the thioether substituents, and θ the thioether cone angles. γ represents an intrinsic parameter for each substrate complex, while α is an electronic and β a steric parameter. Large variations in both electronic and steric properties of the entering ligands indicate that there is no duality behavior in the reactions of thioethers with square-planar metal centers.
Abstract
Abstract Image
Kinetics for complex formation between Pd(H2O)42+ and thioethers of largely varying electronic and steric properties, viz. MeSCH2COOH, (n-Pr)2S, EtSCH2CH2OH, S(CH2CH2CH2OH)2, S(CH2CH2OH)2, EtSCH2COOH, S(CH2COOH)2, S(CH2CH2COOH)2, (i-Pr)2S, (s-Bu)2S, (t-Bu)2S, and protonated thiomorpholine, S(C2H4)2NH2+, has been studied by use of stopped-flow spectrophotometry in an acidic aqueous medium. Second-order rate constants k1298 are 1.61 × 104, 8.0 × 104, 3.79 × 104, 3.69 × 104, 2.21 × 104, 1.84 × 104, 1.91 × 103, 1.34 × 104, 1.52 × 104, 7.75 × 103, 900, and 5.2 × 103 M-1 s-1, respectively. The reactivity toward Pd(H2O)42+ of all thioethers studied so far can be described as a function of their σ-donor properties as expressed by the sum of the Taft constants, ∑σ*, and their steric requirements as defined by cone angles, θ, by use of the equation:  log k1 = (9.9 ± 0.3) − (0.67 ± 0.05)∑σ* − (0.059 ± 0.003)θ. Similarly, second-order rate constants k298 reported previously for reactions between thioethers and Pd(dien)H2O2+ and Pt(dien)Br+ are described by log k298 = (10.5 ± 0.6) − 0.67∑σ* − (0.081 ± 0.006)θ and log k298 = (4.6 ± 0.6) − 0.72∑σ* − (0.080 ± 0.006)θ, respectively. Hence, the reactivity trends of thioethers toward square-planar complexes can be given a general interpretation in terms of intrinsic, electronic, and steric parameters, by use of log k = γ + α∑σ* + βθ. Large variations in both electronic and steric properties of the entering ligands indicate that there is no “duality behavior” in the reactions of thioethers with square-planar metal centers, as claimed in previous literature. No steric threshold is observed for these sterically unhindered systems. There is a rough compensation effect between ΔH1⧧ and ΔS1⧧, i.e. a smaller ΔH1⧧ is usually accompanied by a larger negative ΔS1⧧, indicating that all thioethers react via the same mechanism. It appears that the much lower reactivity observed for the highly branched (t-Bu)2S is primarily caused by a high activation enthalpy. Volumes of activation have been determined for a series of thioethers with a constant cone angle, viz. EtSCH2COOH, S(CH2COOH)2, and S(CH2CH2COOH)2 through high-pressure stopped-flow measurements. Values of ΔV1⧧ are −7.9 ± 0.5, −8.1 ± 0.4, and −7.6 ± 0.3 cm3 mol-1, respectively. These values together with that for Et2S (−8.7 ± 0.1 cm3 mol-1) determined previously shows that variation of electronic properties, steric factors being kept constant, change the reactivity markedly, but have no observable influence on the activation volumes. Stability constants β1 for five palladium thioether complexes derived as the ratio between rate constants for forward and reverse reactions vary between (1.2 ± 0.3) × 104 and (3.2 ± 0.7) × 104 M-1. (Less)
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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
Palladium(II), Thioethers, Complex formation, High-presssure stopped flow, Taft constant, Cone angle, Reaction mechanism, Activation parameters, Stability constants
in
Inorganic Chemistry
volume
35
issue
20
pages
7 pages
publisher
The American Chemical Society
external identifiers
  • scopus:0000270502
ISSN
1520-510X
DOI
10.1021/ic9603518
language
English
LU publication?
yes
id
2a1eaacd-e301-4484-b706-1c4d5e9edbb2
date added to LUP
2017-01-04 17:19:47
date last changed
2017-04-25 22:42:06
@article{2a1eaacd-e301-4484-b706-1c4d5e9edbb2,
  abstract     = {Synopsis<br/>Reactivity trends of thioethers toward square-planar complexes can be generally interpreted by use of an equation of the form:  log k = γ + α∑σ* + βθ, where k denotes second-order rate constants, ∑σ* the sum of Taft constants for the thioether substituents, and θ the thioether cone angles. γ represents an intrinsic parameter for each substrate complex, while α is an electronic and β a steric parameter. Large variations in both electronic and steric properties of the entering ligands indicate that there is no duality behavior in the reactions of thioethers with square-planar metal centers.<br/>Abstract<br/>Abstract Image<br/>Kinetics for complex formation between Pd(H2O)42+ and thioethers of largely varying electronic and steric properties, viz. MeSCH2COOH, (n-Pr)2S, EtSCH2CH2OH, S(CH2CH2CH2OH)2, S(CH2CH2OH)2, EtSCH2COOH, S(CH2COOH)2, S(CH2CH2COOH)2, (i-Pr)2S, (s-Bu)2S, (t-Bu)2S, and protonated thiomorpholine, S(C2H4)2NH2+, has been studied by use of stopped-flow spectrophotometry in an acidic aqueous medium. Second-order rate constants k1298 are 1.61 × 104, 8.0 × 104, 3.79 × 104, 3.69 × 104, 2.21 × 104, 1.84 × 104, 1.91 × 103, 1.34 × 104, 1.52 × 104, 7.75 × 103, 900, and 5.2 × 103 M-1 s-1, respectively. The reactivity toward Pd(H2O)42+ of all thioethers studied so far can be described as a function of their σ-donor properties as expressed by the sum of the Taft constants, ∑σ*, and their steric requirements as defined by cone angles, θ, by use of the equation:  log k1 = (9.9 ± 0.3) − (0.67 ± 0.05)∑σ* − (0.059 ± 0.003)θ. Similarly, second-order rate constants k298 reported previously for reactions between thioethers and Pd(dien)H2O2+ and Pt(dien)Br+ are described by log k298 = (10.5 ± 0.6) − 0.67∑σ* − (0.081 ± 0.006)θ and log k298 = (4.6 ± 0.6) − 0.72∑σ* − (0.080 ± 0.006)θ, respectively. Hence, the reactivity trends of thioethers toward square-planar complexes can be given a general interpretation in terms of intrinsic, electronic, and steric parameters, by use of log k = γ + α∑σ* + βθ. Large variations in both electronic and steric properties of the entering ligands indicate that there is no “duality behavior” in the reactions of thioethers with square-planar metal centers, as claimed in previous literature. No steric threshold is observed for these sterically unhindered systems. There is a rough compensation effect between ΔH1⧧ and ΔS1⧧, i.e. a smaller ΔH1⧧ is usually accompanied by a larger negative ΔS1⧧, indicating that all thioethers react via the same mechanism. It appears that the much lower reactivity observed for the highly branched (t-Bu)2S is primarily caused by a high activation enthalpy. Volumes of activation have been determined for a series of thioethers with a constant cone angle, viz. EtSCH2COOH, S(CH2COOH)2, and S(CH2CH2COOH)2 through high-pressure stopped-flow measurements. Values of ΔV1⧧ are −7.9 ± 0.5, −8.1 ± 0.4, and −7.6 ± 0.3 cm3 mol-1, respectively. These values together with that for Et2S (−8.7 ± 0.1 cm3 mol-1) determined previously shows that variation of electronic properties, steric factors being kept constant, change the reactivity markedly, but have no observable influence on the activation volumes. Stability constants β1 for five palladium thioether complexes derived as the ratio between rate constants for forward and reverse reactions vary between (1.2 ± 0.3) × 104 and (3.2 ± 0.7) × 104 M-1.},
  author       = {Shi, Tiesheng and Elding, Lars Ivar},
  issn         = {1520-510X},
  keyword      = {Palladium(II),Thioethers,Complex formation,High-presssure stopped flow,Taft constant,Cone angle,Reaction mechanism,Activation parameters,Stability constants},
  language     = {eng},
  month        = {09},
  number       = {20},
  pages        = {5941--5947},
  publisher    = {The American Chemical Society},
  series       = {Inorganic Chemistry},
  title        = {Structure-Reactivity Correlations for Complex Formation Reactions between Square-Planar Metal Centers and Thioethers},
  url          = {http://dx.doi.org/10.1021/ic9603518},
  volume       = {35},
  year         = {1996},
}