Kinetics and mechanism of the β-hydride elimination reaction of (1,2-bis(methoxycarbonyl)ethyl)cobalt tetracarbonyl

István Kovács, F. Ungváry, László Markó

Research output: Contribution to journalArticle

8 Citations (Scopus)

Abstract

The title complex, MeO2CCH2CH(CO2Me)Co(CO)4 (1), was found to decompose in alkanes or chlorinated hydrocarbons as solvents quantitatively to Co2(CO)8 and a 1:1 mixture of dimethyl fumarate and dimethyl succinate at room temperature under 1 atm of CO. HCo(CO)4 was trapped in this process either by 1-heptene or Proton Sponge in the form of n-octanoylcobalt tetracarbonyl or a [BH]+[Co(CO)4]- salt, respectively. As model reactions confirmed, the decomposition of 1 consists of two distinct steps such as (1) β-hydride elimination and (2) subsequent fast consumption of HCo(CO)4 in its reaction with 1. Comparative 1H NMR experiments on deuterium labeled MeO2CCHDCH(CO2Me)Co(CO)4 (2) proved that the β-elimination reaction is stereospecific and syn. Consistent with kinetic studies, a modified mechanism of β-elimination is suggested, which includes a pre-equilibrium CO dissociation from 1, a fast intramolecular transformation of the resulting intermediate into a tricarbonyl-hydridoolefincobalt species, which may transfer a hydrogen atom to Co(CO)4 radicals (formed by the homolytic dissociation of Co2(CO)8) in a rate-determining step to yield HCo(CO)4. Together with earlier mechanistic studies on the formation of 1, we showed for alkylcobalt carbonyls for the first time the reversibility of the β-elimination reaction on a molecular level. ΔH = 25.1 (±0.9) kcal mol-1 and ΔS = 5.3 (±0.3) eu were obtained as overall activation parameters. The mechanism of CO dissociation was investigated by kinetic measurements of the 13CO exchange reaction of 1. These studies provided the activation parametes ΔH = 7.7 (±0.6) kcal mol-1 and ΔS = -44.2 (±0.1) eu, which could be best explained by an intramolecular associative pathway. Accordingly, the gain in energy and the considerably more structured transition state resulting from the weak coordination of a carboxylic oxygen to cobalt to form a five-membered metallacycle may account for the particularly low values of activation enthalpy and entropy, respectively.

Original languageEnglish
Pages (from-to)1927-1933
Number of pages7
JournalOrganometallics
Volume13
Issue number5
Publication statusPublished - 1994

Fingerprint

Cobalt
Hydrides
hydrides
elimination
cobalt
Chemical activation
Kinetics
kinetics
Chlorinated Hydrocarbons
activation
dissociation
Alkanes
Deuterium
Protons
Hydrogen
Enthalpy
Entropy
Salts
Nuclear magnetic resonance
Oxygen

ASJC Scopus subject areas

  • Inorganic Chemistry
  • Organic Chemistry

Cite this

Kinetics and mechanism of the β-hydride elimination reaction of (1,2-bis(methoxycarbonyl)ethyl)cobalt tetracarbonyl. / Kovács, István; Ungváry, F.; Markó, László.

In: Organometallics, Vol. 13, No. 5, 1994, p. 1927-1933.

Research output: Contribution to journalArticle

@article{13155630847f4b4db623268f0abc1459,
title = "Kinetics and mechanism of the β-hydride elimination reaction of (1,2-bis(methoxycarbonyl)ethyl)cobalt tetracarbonyl",
abstract = "The title complex, MeO2CCH2CH(CO2Me)Co(CO)4 (1), was found to decompose in alkanes or chlorinated hydrocarbons as solvents quantitatively to Co2(CO)8 and a 1:1 mixture of dimethyl fumarate and dimethyl succinate at room temperature under 1 atm of CO. HCo(CO)4 was trapped in this process either by 1-heptene or Proton Sponge in the form of n-octanoylcobalt tetracarbonyl or a [BH]+[Co(CO)4]- salt, respectively. As model reactions confirmed, the decomposition of 1 consists of two distinct steps such as (1) β-hydride elimination and (2) subsequent fast consumption of HCo(CO)4 in its reaction with 1. Comparative 1H NMR experiments on deuterium labeled MeO2CCHDCH(CO2Me)Co(CO)4 (2) proved that the β-elimination reaction is stereospecific and syn. Consistent with kinetic studies, a modified mechanism of β-elimination is suggested, which includes a pre-equilibrium CO dissociation from 1, a fast intramolecular transformation of the resulting intermediate into a tricarbonyl-hydridoolefincobalt species, which may transfer a hydrogen atom to Co(CO)4 radicals (formed by the homolytic dissociation of Co2(CO)8) in a rate-determining step to yield HCo(CO)4. Together with earlier mechanistic studies on the formation of 1, we showed for alkylcobalt carbonyls for the first time the reversibility of the β-elimination reaction on a molecular level. ΔH‡ = 25.1 (±0.9) kcal mol-1 and ΔS‡ = 5.3 (±0.3) eu were obtained as overall activation parameters. The mechanism of CO dissociation was investigated by kinetic measurements of the 13CO exchange reaction of 1. These studies provided the activation parametes ΔH‡ = 7.7 (±0.6) kcal mol-1 and ΔS‡ = -44.2 (±0.1) eu, which could be best explained by an intramolecular associative pathway. Accordingly, the gain in energy and the considerably more structured transition state resulting from the weak coordination of a carboxylic oxygen to cobalt to form a five-membered metallacycle may account for the particularly low values of activation enthalpy and entropy, respectively.",
author = "Istv{\'a}n Kov{\'a}cs and F. Ungv{\'a}ry and L{\'a}szl{\'o} Mark{\'o}",
year = "1994",
language = "English",
volume = "13",
pages = "1927--1933",
journal = "Organometallics",
issn = "0276-7333",
publisher = "American Chemical Society",
number = "5",

}

TY - JOUR

T1 - Kinetics and mechanism of the β-hydride elimination reaction of (1,2-bis(methoxycarbonyl)ethyl)cobalt tetracarbonyl

AU - Kovács, István

AU - Ungváry, F.

AU - Markó, László

PY - 1994

Y1 - 1994

N2 - The title complex, MeO2CCH2CH(CO2Me)Co(CO)4 (1), was found to decompose in alkanes or chlorinated hydrocarbons as solvents quantitatively to Co2(CO)8 and a 1:1 mixture of dimethyl fumarate and dimethyl succinate at room temperature under 1 atm of CO. HCo(CO)4 was trapped in this process either by 1-heptene or Proton Sponge in the form of n-octanoylcobalt tetracarbonyl or a [BH]+[Co(CO)4]- salt, respectively. As model reactions confirmed, the decomposition of 1 consists of two distinct steps such as (1) β-hydride elimination and (2) subsequent fast consumption of HCo(CO)4 in its reaction with 1. Comparative 1H NMR experiments on deuterium labeled MeO2CCHDCH(CO2Me)Co(CO)4 (2) proved that the β-elimination reaction is stereospecific and syn. Consistent with kinetic studies, a modified mechanism of β-elimination is suggested, which includes a pre-equilibrium CO dissociation from 1, a fast intramolecular transformation of the resulting intermediate into a tricarbonyl-hydridoolefincobalt species, which may transfer a hydrogen atom to Co(CO)4 radicals (formed by the homolytic dissociation of Co2(CO)8) in a rate-determining step to yield HCo(CO)4. Together with earlier mechanistic studies on the formation of 1, we showed for alkylcobalt carbonyls for the first time the reversibility of the β-elimination reaction on a molecular level. ΔH‡ = 25.1 (±0.9) kcal mol-1 and ΔS‡ = 5.3 (±0.3) eu were obtained as overall activation parameters. The mechanism of CO dissociation was investigated by kinetic measurements of the 13CO exchange reaction of 1. These studies provided the activation parametes ΔH‡ = 7.7 (±0.6) kcal mol-1 and ΔS‡ = -44.2 (±0.1) eu, which could be best explained by an intramolecular associative pathway. Accordingly, the gain in energy and the considerably more structured transition state resulting from the weak coordination of a carboxylic oxygen to cobalt to form a five-membered metallacycle may account for the particularly low values of activation enthalpy and entropy, respectively.

AB - The title complex, MeO2CCH2CH(CO2Me)Co(CO)4 (1), was found to decompose in alkanes or chlorinated hydrocarbons as solvents quantitatively to Co2(CO)8 and a 1:1 mixture of dimethyl fumarate and dimethyl succinate at room temperature under 1 atm of CO. HCo(CO)4 was trapped in this process either by 1-heptene or Proton Sponge in the form of n-octanoylcobalt tetracarbonyl or a [BH]+[Co(CO)4]- salt, respectively. As model reactions confirmed, the decomposition of 1 consists of two distinct steps such as (1) β-hydride elimination and (2) subsequent fast consumption of HCo(CO)4 in its reaction with 1. Comparative 1H NMR experiments on deuterium labeled MeO2CCHDCH(CO2Me)Co(CO)4 (2) proved that the β-elimination reaction is stereospecific and syn. Consistent with kinetic studies, a modified mechanism of β-elimination is suggested, which includes a pre-equilibrium CO dissociation from 1, a fast intramolecular transformation of the resulting intermediate into a tricarbonyl-hydridoolefincobalt species, which may transfer a hydrogen atom to Co(CO)4 radicals (formed by the homolytic dissociation of Co2(CO)8) in a rate-determining step to yield HCo(CO)4. Together with earlier mechanistic studies on the formation of 1, we showed for alkylcobalt carbonyls for the first time the reversibility of the β-elimination reaction on a molecular level. ΔH‡ = 25.1 (±0.9) kcal mol-1 and ΔS‡ = 5.3 (±0.3) eu were obtained as overall activation parameters. The mechanism of CO dissociation was investigated by kinetic measurements of the 13CO exchange reaction of 1. These studies provided the activation parametes ΔH‡ = 7.7 (±0.6) kcal mol-1 and ΔS‡ = -44.2 (±0.1) eu, which could be best explained by an intramolecular associative pathway. Accordingly, the gain in energy and the considerably more structured transition state resulting from the weak coordination of a carboxylic oxygen to cobalt to form a five-membered metallacycle may account for the particularly low values of activation enthalpy and entropy, respectively.

UR - http://www.scopus.com/inward/record.url?scp=0011628128&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=0011628128&partnerID=8YFLogxK

M3 - Article

VL - 13

SP - 1927

EP - 1933

JO - Organometallics

JF - Organometallics

SN - 0276-7333

IS - 5

ER -