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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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Schematic representation of three cis–trans isomerization mechanisms investigated for [RuCl4(NO)(Hind)]−: dissociative (A), associative (B), and twist (C).The involved transition states and the reaction intermediates areshown, together with the most relevant geometrical parameters (inÅ and degrees) obtained at the B3LYP/6-31G* level of theory inthe gas phase. The relative energies are calculated at the PCM-B2GP-PLYP/6-311G*//B3LYP/6-31G*level of theory. The labels cis-ts, ts, and trans-ts refer to transitionstates, while cis-min and trans-min are intermediates. For a better illustration of the twist mechanism(c), the letters a, b, and c mark the NO–Cl–Cl triangle. Upon the isomerization,the triangle rotates around the ruthenium atom, as shown in the figure.
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fig9: Schematic representation of three cis–trans isomerization mechanisms investigated for [RuCl4(NO)(Hind)]−: dissociative (A), associative (B), and twist (C).The involved transition states and the reaction intermediates areshown, together with the most relevant geometrical parameters (inÅ and degrees) obtained at the B3LYP/6-31G* level of theory inthe gas phase. The relative energies are calculated at the PCM-B2GP-PLYP/6-311G*//B3LYP/6-31G*level of theory. The labels cis-ts, ts, and trans-ts refer to transitionstates, while cis-min and trans-min are intermediates. For a better illustration of the twist mechanism(c), the letters a, b, and c mark the NO–Cl–Cl triangle. Upon the isomerization,the triangle rotates around the ruthenium atom, as shown in the figure.

Mentions: In the following, wediscuss the cis↔trans isomerizationmechanism of the [RuCl4(NO)(Hind)]− complex.We present and compare activation energies for three different isomerizationpathways: the dissociative mechanism with intermediates, the associativemechanism, and the twist mechanism. The outlines for the three mechanismsshowing the involved transition states and intermediates are givenin Figure 9, showing the most relevant geometricalparameters. All the optimized values can be found in the Supporting Information (Tables S1–S9).Although the mechanisms are described only in the cis → trans direction, they are thermodynamicallyreversible, and hence the described reaction paths are also validfor the reverse reaction.


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)

Schematic representation of three cis–trans isomerization mechanisms investigated for [RuCl4(NO)(Hind)]−: dissociative (A), associative (B), and twist (C).The involved transition states and the reaction intermediates areshown, together with the most relevant geometrical parameters (inÅ and degrees) obtained at the B3LYP/6-31G* level of theory inthe gas phase. The relative energies are calculated at the PCM-B2GP-PLYP/6-311G*//B3LYP/6-31G*level of theory. The labels cis-ts, ts, and trans-ts refer to transitionstates, while cis-min and trans-min are intermediates. For a better illustration of the twist mechanism(c), the letters a, b, and c mark the NO–Cl–Cl triangle. Upon the isomerization,the triangle rotates around the ruthenium atom, as shown in the figure.
© Copyright Policy
Related In: Results  -  Collection

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

fig9: Schematic representation of three cis–trans isomerization mechanisms investigated for [RuCl4(NO)(Hind)]−: dissociative (A), associative (B), and twist (C).The involved transition states and the reaction intermediates areshown, together with the most relevant geometrical parameters (inÅ and degrees) obtained at the B3LYP/6-31G* level of theory inthe gas phase. The relative energies are calculated at the PCM-B2GP-PLYP/6-311G*//B3LYP/6-31G*level of theory. The labels cis-ts, ts, and trans-ts refer to transitionstates, while cis-min and trans-min are intermediates. For a better illustration of the twist mechanism(c), the letters a, b, and c mark the NO–Cl–Cl triangle. Upon the isomerization,the triangle rotates around the ruthenium atom, as shown in the figure.
Mentions: In the following, wediscuss the cis↔trans isomerizationmechanism of the [RuCl4(NO)(Hind)]− complex.We present and compare activation energies for three different isomerizationpathways: the dissociative mechanism with intermediates, the associativemechanism, and the twist mechanism. The outlines for the three mechanismsshowing the involved transition states and intermediates are givenin Figure 9, showing the most relevant geometricalparameters. All the optimized values can be found in the Supporting Information (Tables S1–S9).Although the mechanisms are described only in the cis → trans direction, they are thermodynamicallyreversible, and hence the described reaction paths are also validfor the reverse reaction.

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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