Preparation, crystal structures and isomerization kinetics of cis- and trans-[Co(dtc)2(PHPh2)2]+: Thermodynamically and kinetically stable cobalt(III)-P bonds through interplay of σ-donicity, π-acidity, and steric bulkiness

Satoshi Iwatsuki, Takayoshi Suzuki, Atsushi Hasegawa, Shigenobu Funahashi, Kazuo Kashiwabara, Hideo D. Takagi

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Abstract

Novel cobalt(III)-diphenylphosphine complexes, cis- and trans-[Co(dtc)2(PHPh)2)2]+, were synthesized and structurally characterized by X-ray crystallographic analyses and spectroscopic methods. The Co-P bond lengths in both isomers were shorter than those in the analogous cobalt(III)-bis(tertiary phosphine) complexes with sterically less bulky but more basic phosphine ligands: Co-P(1) = 2.2340(6) and Co-P(2) = 2.2258(7) Å for the cis-isomer, and Co-P = 2.276(1) Å for the trans isomer. The title complexes also exhibited a unique dynamic behavior: cis to trans isomerization was induced by irradiation with visible light, while thermal trans to cis isomerization took place at elevated temperatures. The absorbance change for the trans to cis isomerization reaction exhibited multi-exponential kinetic traces when no free PHPh2 was present in the solution. Such a complicated kinetic behavior was explained either by the slow dissociation of coordinated PHPh2 or by the abstraction of a P-H proton from coordinated PHPh2 through an acid-base interaction with trace water in the bulk solvent. By addition of an excess amount of PHPh2, the dissociation of coordinated PHPh2 as well as the basicity of impure water was suppressed, and a first-order kinetic trace was observed. Kinetic studies with excess free PHPh2 in acetonitrile revealed that the isomerization reaction takes place via an intramolecular twist mechanism: ΔH* = 120 ± 1 kJ mol-1 and ΔS* = 50 ± 18 J mol-1 K-1. AOM calculations indicate that the twist mechanism involves a spin state change (1A1g to 5A1′) during the activation process. The importance of the π-acidity of PHPh2 together with the cooperative effect of the spectator ligand (dtc-) was suggested to explain the thermodynamic and kinetic behaviors of these complexes.

Original languageEnglish
Pages (from-to)3593-3602
Number of pages10
JournalJournal of the Chemical Society, Dalton Transactions
Issue number18
Publication statusPublished - 2002
Externally publishedYes

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Isomerization
Cobalt
phosphine
Acidity
Crystal structure
Kinetics
Isomers
Ligands
Water
Bond length
Alkalinity
Protons
Chemical activation
Irradiation
Thermodynamics
X rays
Acids
Temperature

ASJC Scopus subject areas

  • Chemistry(all)

Cite this

@article{a58a1ba361d6461e85a91309eb0718fd,
title = "Preparation, crystal structures and isomerization kinetics of cis- and trans-[Co(dtc)2(PHPh2)2]+: Thermodynamically and kinetically stable cobalt(III)-P bonds through interplay of σ-donicity, π-acidity, and steric bulkiness",
abstract = "Novel cobalt(III)-diphenylphosphine complexes, cis- and trans-[Co(dtc)2(PHPh)2)2]+, were synthesized and structurally characterized by X-ray crystallographic analyses and spectroscopic methods. The Co-P bond lengths in both isomers were shorter than those in the analogous cobalt(III)-bis(tertiary phosphine) complexes with sterically less bulky but more basic phosphine ligands: Co-P(1) = 2.2340(6) and Co-P(2) = 2.2258(7) {\AA} for the cis-isomer, and Co-P = 2.276(1) {\AA} for the trans isomer. The title complexes also exhibited a unique dynamic behavior: cis to trans isomerization was induced by irradiation with visible light, while thermal trans to cis isomerization took place at elevated temperatures. The absorbance change for the trans to cis isomerization reaction exhibited multi-exponential kinetic traces when no free PHPh2 was present in the solution. Such a complicated kinetic behavior was explained either by the slow dissociation of coordinated PHPh2 or by the abstraction of a P-H proton from coordinated PHPh2 through an acid-base interaction with trace water in the bulk solvent. By addition of an excess amount of PHPh2, the dissociation of coordinated PHPh2 as well as the basicity of impure water was suppressed, and a first-order kinetic trace was observed. Kinetic studies with excess free PHPh2 in acetonitrile revealed that the isomerization reaction takes place via an intramolecular twist mechanism: ΔH* = 120 ± 1 kJ mol-1 and ΔS* = 50 ± 18 J mol-1 K-1. AOM calculations indicate that the twist mechanism involves a spin state change (1A1g to 5A1′) during the activation process. The importance of the π-acidity of PHPh2 together with the cooperative effect of the spectator ligand (dtc-) was suggested to explain the thermodynamic and kinetic behaviors of these complexes.",
author = "Satoshi Iwatsuki and Takayoshi Suzuki and Atsushi Hasegawa and Shigenobu Funahashi and Kazuo Kashiwabara and Takagi, {Hideo D.}",
year = "2002",
language = "English",
pages = "3593--3602",
journal = "Dalton Transactions",
issn = "1477-9226",
publisher = "Royal Society of Chemistry",
number = "18",

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TY - JOUR

T1 - Preparation, crystal structures and isomerization kinetics of cis- and trans-[Co(dtc)2(PHPh2)2]+

T2 - Thermodynamically and kinetically stable cobalt(III)-P bonds through interplay of σ-donicity, π-acidity, and steric bulkiness

AU - Iwatsuki, Satoshi

AU - Suzuki, Takayoshi

AU - Hasegawa, Atsushi

AU - Funahashi, Shigenobu

AU - Kashiwabara, Kazuo

AU - Takagi, Hideo D.

PY - 2002

Y1 - 2002

N2 - Novel cobalt(III)-diphenylphosphine complexes, cis- and trans-[Co(dtc)2(PHPh)2)2]+, were synthesized and structurally characterized by X-ray crystallographic analyses and spectroscopic methods. The Co-P bond lengths in both isomers were shorter than those in the analogous cobalt(III)-bis(tertiary phosphine) complexes with sterically less bulky but more basic phosphine ligands: Co-P(1) = 2.2340(6) and Co-P(2) = 2.2258(7) Å for the cis-isomer, and Co-P = 2.276(1) Å for the trans isomer. The title complexes also exhibited a unique dynamic behavior: cis to trans isomerization was induced by irradiation with visible light, while thermal trans to cis isomerization took place at elevated temperatures. The absorbance change for the trans to cis isomerization reaction exhibited multi-exponential kinetic traces when no free PHPh2 was present in the solution. Such a complicated kinetic behavior was explained either by the slow dissociation of coordinated PHPh2 or by the abstraction of a P-H proton from coordinated PHPh2 through an acid-base interaction with trace water in the bulk solvent. By addition of an excess amount of PHPh2, the dissociation of coordinated PHPh2 as well as the basicity of impure water was suppressed, and a first-order kinetic trace was observed. Kinetic studies with excess free PHPh2 in acetonitrile revealed that the isomerization reaction takes place via an intramolecular twist mechanism: ΔH* = 120 ± 1 kJ mol-1 and ΔS* = 50 ± 18 J mol-1 K-1. AOM calculations indicate that the twist mechanism involves a spin state change (1A1g to 5A1′) during the activation process. The importance of the π-acidity of PHPh2 together with the cooperative effect of the spectator ligand (dtc-) was suggested to explain the thermodynamic and kinetic behaviors of these complexes.

AB - Novel cobalt(III)-diphenylphosphine complexes, cis- and trans-[Co(dtc)2(PHPh)2)2]+, were synthesized and structurally characterized by X-ray crystallographic analyses and spectroscopic methods. The Co-P bond lengths in both isomers were shorter than those in the analogous cobalt(III)-bis(tertiary phosphine) complexes with sterically less bulky but more basic phosphine ligands: Co-P(1) = 2.2340(6) and Co-P(2) = 2.2258(7) Å for the cis-isomer, and Co-P = 2.276(1) Å for the trans isomer. The title complexes also exhibited a unique dynamic behavior: cis to trans isomerization was induced by irradiation with visible light, while thermal trans to cis isomerization took place at elevated temperatures. The absorbance change for the trans to cis isomerization reaction exhibited multi-exponential kinetic traces when no free PHPh2 was present in the solution. Such a complicated kinetic behavior was explained either by the slow dissociation of coordinated PHPh2 or by the abstraction of a P-H proton from coordinated PHPh2 through an acid-base interaction with trace water in the bulk solvent. By addition of an excess amount of PHPh2, the dissociation of coordinated PHPh2 as well as the basicity of impure water was suppressed, and a first-order kinetic trace was observed. Kinetic studies with excess free PHPh2 in acetonitrile revealed that the isomerization reaction takes place via an intramolecular twist mechanism: ΔH* = 120 ± 1 kJ mol-1 and ΔS* = 50 ± 18 J mol-1 K-1. AOM calculations indicate that the twist mechanism involves a spin state change (1A1g to 5A1′) during the activation process. The importance of the π-acidity of PHPh2 together with the cooperative effect of the spectator ligand (dtc-) was suggested to explain the thermodynamic and kinetic behaviors of these complexes.

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