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Mechanism elucidation of the cis-trans isomerization of an azole ruthenium-nitrosyl complex and its osmium counterpart.

Gavriluta A, Büchel GE, Freitag L, Novitchi G, Tommasino JB, Jeanneau E, Kuhn PS, González L, Arion VB, Luneau D - Inorg Chem (2013)

Bottom Line: The value for the activation energy found for the dissociative mechanism is in good agreement with experimental activation enthalpy.Electrochemical investigation provides further evidence for higher reactivity of ruthenium complexes compared to that of osmium counterparts and shows that intramolecular electron transfer reactions do not affect the isomerization process.A dissociative mechanism of cis↔trans isomerization has been proposed for both ruthenium and osmium complexes.

View Article: PubMed Central - PubMed

Affiliation: Université Claude Bernard Lyon 1, Laboratoire des Multimatériaux et Interfaces (UMR 5615), Campus de la Doua, 69622 Villeurbanne Cedex, France.

ABSTRACT
Synthesis and X-ray diffraction structures of cis and trans isomers of ruthenium and osmium metal complexes of general formulas (nBu4N)[cis-MCl4(NO)(Hind)], where M = Ru (1) and Os (3), and (nBu4N)[trans-MCl4(NO)(Hind)], where M = Ru (2) and Os (4) and Hind = 1H-indazole are reported. Interconversion between cis and trans isomers at high temperatures (80-130 °C) has been observed and studied by NMR spectroscopy. Kinetic data indicate that isomerizations correspond to reversible first order reactions. The rates of isomerization reactions even at 110 °C are very low with rate constants of 10(-5) s(-1) and 10(-6) s(-1) for ruthenium and osmium complexes, respectively, and the estimated rate constants of isomerization at room temperature are of ca. 10(-10) s(-1). The activation parameters, which have been obtained from fitting the reaction rates at different temperatures to the Eyring equation for ruthenium [ΔH(cis-trans)‡ = 122.8 ± 1.3; ΔH(trans-cis)‡ = 138.8 ± 1.0 kJ/mol; ΔS(cis-trans)‡ = -18.7 ± 3.6; ΔS(trans-cis)‡ = 31.8 ± 2.7 J/(mol·K)] and osmium [ΔH(cis-trans)‡ = 200.7 ± 0.7; ΔH(trans-cis)‡ = 168.2 ± 0.6 kJ/mol; ΔS(cis-trans)‡ = 142.7 ± 8.9; ΔS(trans-cis)‡ = 85.9 ± 3.9 J/(mol·K)] reflect the inertness of these systems. The entropy of activation for the osmium complexes is highly positive and suggests the dissociative mechanism of isomerization. In the case of ruthenium, the activation entropy for the cis to trans isomerization is negative [-18.6 J/(mol·K)], while being positive [31.0 J/(mol·K)] for the trans to cis conversion. The thermodynamic parameters for cis to trans isomerization of [RuCl4(NO)(Hind)]-, viz. ΔH° = 13.5 ± 1.5 kJ/mol and ΔS° = -5.2 ± 3.4 J/(mol·K) indicate the low difference between the energies of cis and trans isomers. The theoretical calculation has been carried out on isomerization of ruthenium complexes with DFT methods. The dissociative, associative, and intramolecular twist isomerization mechanisms have been considered. The value for the activation energy found for the dissociative mechanism is in good agreement with experimental activation enthalpy. Electrochemical investigation provides further evidence for higher reactivity of ruthenium complexes compared to that of osmium counterparts and shows that intramolecular electron transfer reactions do not affect the isomerization process. A dissociative mechanism of cis↔trans isomerization has been proposed for both ruthenium and osmium complexes.

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Evolution of 1H NMR spectra (300MHz) of the [trans-OsCl4(NO)(Hind)]− isomer in the NH region as a functionof time (τ = [0–3] × 105 s) at 120 °Cin C2D2Cl4 (C0 = 15.26 mmol/L) showing the formation of the cis isomer (for complete aromatic region spectrum, see Supporting Information Figure S5).
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fig4: Evolution of 1H NMR spectra (300MHz) of the [trans-OsCl4(NO)(Hind)]− isomer in the NH region as a functionof time (τ = [0–3] × 105 s) at 120 °Cin C2D2Cl4 (C0 = 15.26 mmol/L) showing the formation of the cis isomer (for complete aromatic region spectrum, see Supporting Information Figure S5).

Mentions: A typical series of time-dependent 1H NMR spectraupon isomerization of [trans-RuCl4(NO)(Hind)]− to [cis-RuCl4(NO)(Hind)]− ([t–c]) and [cis-RuCl4(NO)(Hind)]− to [trans-RuCl4(NO)(Hind)]− ([c–t]) is shown inFigure 3, while that of [trans-OsCl4(NO)(Hind)]− conversion into [cis-OsCl4(NO)(Hind)]− and viceversa is displayed in Figure 4. From Figures 3a and 4, a progressive decreaseof the NH signal intensity with time, corresponding tothe trans isomer, and an increase of the signal correspondingto the cis isomer is seen. After 72 h of heatingat 100 °C, [trans-RuCl4(NO)(Hind)]− is partially converted into [cis-RuCl4(NO)(Hind)]−, and the trans–cis equilibrium is reached. Similarly, starting from the [cis-RuCl4(NO)(Hind)]− isomer, the sameequilibrium ratio between the cis and trans isomers is reached after 72 h of heating the solution at 100 °C.These time-dependent NMR spectra and the same equilibrium ratios between cis and trans isomers indicate the reversibilityof the isomerization process.


Mechanism elucidation of the cis-trans isomerization of an azole ruthenium-nitrosyl complex and its osmium counterpart.

Gavriluta A, Büchel GE, Freitag L, Novitchi G, Tommasino JB, Jeanneau E, Kuhn PS, González L, Arion VB, Luneau D - Inorg Chem (2013)

Evolution of 1H NMR spectra (300MHz) of the [trans-OsCl4(NO)(Hind)]− isomer in the NH region as a functionof time (τ = [0–3] × 105 s) at 120 °Cin C2D2Cl4 (C0 = 15.26 mmol/L) showing the formation of the cis isomer (for complete aromatic region spectrum, see Supporting Information Figure S5).
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3673021&req=5

fig4: Evolution of 1H NMR spectra (300MHz) of the [trans-OsCl4(NO)(Hind)]− isomer in the NH region as a functionof time (τ = [0–3] × 105 s) at 120 °Cin C2D2Cl4 (C0 = 15.26 mmol/L) showing the formation of the cis isomer (for complete aromatic region spectrum, see Supporting Information Figure S5).
Mentions: A typical series of time-dependent 1H NMR spectraupon isomerization of [trans-RuCl4(NO)(Hind)]− to [cis-RuCl4(NO)(Hind)]− ([t–c]) and [cis-RuCl4(NO)(Hind)]− to [trans-RuCl4(NO)(Hind)]− ([c–t]) is shown inFigure 3, while that of [trans-OsCl4(NO)(Hind)]− conversion into [cis-OsCl4(NO)(Hind)]− and viceversa is displayed in Figure 4. From Figures 3a and 4, a progressive decreaseof the NH signal intensity with time, corresponding tothe trans isomer, and an increase of the signal correspondingto the cis isomer is seen. After 72 h of heatingat 100 °C, [trans-RuCl4(NO)(Hind)]− is partially converted into [cis-RuCl4(NO)(Hind)]−, and the trans–cis equilibrium is reached. Similarly, starting from the [cis-RuCl4(NO)(Hind)]− isomer, the sameequilibrium ratio between the cis and trans isomers is reached after 72 h of heating the solution at 100 °C.These time-dependent NMR spectra and the same equilibrium ratios between cis and trans isomers indicate the reversibilityof the isomerization process.

Bottom Line: The value for the activation energy found for the dissociative mechanism is in good agreement with experimental activation enthalpy.Electrochemical investigation provides further evidence for higher reactivity of ruthenium complexes compared to that of osmium counterparts and shows that intramolecular electron transfer reactions do not affect the isomerization process.A dissociative mechanism of cis↔trans isomerization has been proposed for both ruthenium and osmium complexes.

View Article: PubMed Central - PubMed

Affiliation: Université Claude Bernard Lyon 1, Laboratoire des Multimatériaux et Interfaces (UMR 5615), Campus de la Doua, 69622 Villeurbanne Cedex, France.

ABSTRACT
Synthesis and X-ray diffraction structures of cis and trans isomers of ruthenium and osmium metal complexes of general formulas (nBu4N)[cis-MCl4(NO)(Hind)], where M = Ru (1) and Os (3), and (nBu4N)[trans-MCl4(NO)(Hind)], where M = Ru (2) and Os (4) and Hind = 1H-indazole are reported. Interconversion between cis and trans isomers at high temperatures (80-130 °C) has been observed and studied by NMR spectroscopy. Kinetic data indicate that isomerizations correspond to reversible first order reactions. The rates of isomerization reactions even at 110 °C are very low with rate constants of 10(-5) s(-1) and 10(-6) s(-1) for ruthenium and osmium complexes, respectively, and the estimated rate constants of isomerization at room temperature are of ca. 10(-10) s(-1). The activation parameters, which have been obtained from fitting the reaction rates at different temperatures to the Eyring equation for ruthenium [ΔH(cis-trans)‡ = 122.8 ± 1.3; ΔH(trans-cis)‡ = 138.8 ± 1.0 kJ/mol; ΔS(cis-trans)‡ = -18.7 ± 3.6; ΔS(trans-cis)‡ = 31.8 ± 2.7 J/(mol·K)] and osmium [ΔH(cis-trans)‡ = 200.7 ± 0.7; ΔH(trans-cis)‡ = 168.2 ± 0.6 kJ/mol; ΔS(cis-trans)‡ = 142.7 ± 8.9; ΔS(trans-cis)‡ = 85.9 ± 3.9 J/(mol·K)] reflect the inertness of these systems. The entropy of activation for the osmium complexes is highly positive and suggests the dissociative mechanism of isomerization. In the case of ruthenium, the activation entropy for the cis to trans isomerization is negative [-18.6 J/(mol·K)], while being positive [31.0 J/(mol·K)] for the trans to cis conversion. The thermodynamic parameters for cis to trans isomerization of [RuCl4(NO)(Hind)]-, viz. ΔH° = 13.5 ± 1.5 kJ/mol and ΔS° = -5.2 ± 3.4 J/(mol·K) indicate the low difference between the energies of cis and trans isomers. The theoretical calculation has been carried out on isomerization of ruthenium complexes with DFT methods. The dissociative, associative, and intramolecular twist isomerization mechanisms have been considered. The value for the activation energy found for the dissociative mechanism is in good agreement with experimental activation enthalpy. Electrochemical investigation provides further evidence for higher reactivity of ruthenium complexes compared to that of osmium counterparts and shows that intramolecular electron transfer reactions do not affect the isomerization process. A dissociative mechanism of cis↔trans isomerization has been proposed for both ruthenium and osmium complexes.

Show MeSH
Related in: MedlinePlus