Molecular Analogs of Surface Species. 3. The Mechanism of the Regioselective Homogeneous Hydrogenation of Benzothiophene by Use of [Rh(COD)(PPh3)2]PF6 as the Catalyst Precursor. Kinetic and Theoretical Study

Roberto A. Sánchez-Delgado; Verónica Herrera; Luis Rincón; Antida Andriollo; Gonzalo Martín

doi:10.1021/om00014a029

Molecular Analogs of Surface Species. 3. The Mechanism of the Regioselective Homogeneous Hydrogenation of Benzothiophene by Use of [Rh(COD)(PPh₃)₂]PF₆ as the Catalyst Precursor. Kinetic and Theoretical Study

Roberto A. Sánchez-Delgado^*
, Verónica Herrera
, Luis Rincón
, Antida Andriollo
, Gonzalo Martín

^*Autor correspondiente de este trabajo

Instituto Venezolano de Investigaciones Científicas (I.V.I.C.)

Producción científica: Contribución a una revista › Artículo › revisión exhaustiva

41 Citas (Scopus)

Resumen

The mechanism of the regioselective hydrogenation of benzo[b]thiophene (BT) to 2,3- dihydrobenzo[b]thiophene (DHBT) in 2-methoxyethanol solution at 125 °C and ambient or subambient pressure of H₂, using [Rh(COD)(PPh₃)₂]PF₆ (1) (COD = 1,3-cyclooctadiene) as the catalyst precursor has been investigated by a combination of kinetic, chemical, and theoretical methods. The kinetic study led to a rate law r_i= k₇K₆ [Rh]₀[H₂]/(1 + K₆[H₂]), where (k_cat)_exp = k₇K₆ = 0.726 M^-1 s^-1, k₇ = 3.70 × 10^-2 s^-1, and K₆ = 19.61 M^-1. The calculated activation parameters are ΔH^‡ = 20.1 ± 0.9 kcal/mol, ΔS^‡ = −11.1 ± 0.8 eu, and ΔG^‡ = 23 ± 3 kcal/mol. 1 probably reacts with hydrogen to produce an unstable intermediate [RhH₂(η¹-S-BT)₂(PPh₃)₂]⁺ which evolves into [Rh(π-BT) (PPh₃)₂]⁺, where BT is likely to be η⁵-bonded through the thiophene ring. Semiempirical (CNDO) theoretical calculations on the interactions of the fragment [Rh-(PH₃)₂]⁺ with BT revealed that both η⁵-bonding through the thiophene ring and η⁶-bonding through the benzene ring are possible; in the former case, the bonding is dominated by donation from a filled 5a′ BT orbital localized mainly on the S lone pair to empty 3a₁ and 2b₁ metal orbitals, whereas in the latter the main interaction is donation from a delocalized 4a′ BT orbital to an empty b₂ metal orbital. The dihydride [Rh(BT)(H)₂(PH₃)₂]⁺ which is formed by reaction of [(η⁵-BT)Rh(PH₃)₂]⁺ with H₂ may contain BT coordinated η¹-S, η²-C₂=C₃ or η⁴; [Rh(η⁴-BT)(H)₂(PH₃)₂]⁺ was found to be more stable than [Rh(η¹-BT)(H)₂(PH₃)₂]⁺ and [Rh(η²-BT)- (H)₂(PH₃)₂]⁺. The largest activation of the C=C bond of the thiophene moiety is produced by the η² mode of bonding. All this information leads to a hydrogenation mechanism in which the active species is most probably the 18 electron π-bonded species [Rh(η⁵-BT)(PPh₃)₂]⁺, which is in equilibrium with an olefin-like complex [Rh(H)₂(η²-BT) (PPh₃)₂]⁺. The rate determining step of the catalytic reaction is the transfer of hydrides from Rh to η²-BT, to yield [Rh(η¹-SDHBT)(PPh₃)₂]⁺; subsequent rapid reaction with BT liberates the product and restarts the catalytic cycle. This mechanism provides a good model for understanding the initial hydrogenation step in the heterogeneous hydrodesulfurization of BT on solid catalysts.

Idioma original	Inglés
Páginas (desde-hasta)	553-561
Número de páginas	9
Publicación	Organometallics
Volumen	13
N.º	2
DOI	https://doi.org/10.1021/om00014a029
Estado	Publicada - 1 feb. 1994
Publicado de forma externa	Sí

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@article{5b68352610a743ccbd24d3f3c2953881,

title = "Molecular Analogs of Surface Species. 3. The Mechanism of the Regioselective Homogeneous Hydrogenation of Benzothiophene by Use of [Rh(COD)(PPh3)2]PF6 as the Catalyst Precursor. Kinetic and Theoretical Study",

abstract = "The mechanism of the regioselective hydrogenation of benzo[b]thiophene (BT) to 2,3- dihydrobenzo[b]thiophene (DHBT) in 2-methoxyethanol solution at 125 °C and ambient or subambient pressure of H2, using [Rh(COD)(PPh3)2]PF6 (1) (COD = 1,3-cyclooctadiene) as the catalyst precursor has been investigated by a combination of kinetic, chemical, and theoretical methods. The kinetic study led to a rate law ri= k7K6 [Rh]0[H2]/(1 + K6[H2]), where (kcat)exp = k7K6 = 0.726 M-1 s-1, k7 = 3.70 × 10-2 s-1, and K6 = 19.61 M-1. The calculated activation parameters are ΔH‡ = 20.1 ± 0.9 kcal/mol, ΔS‡ = −11.1 ± 0.8 eu, and ΔG‡ = 23 ± 3 kcal/mol. 1 probably reacts with hydrogen to produce an unstable intermediate [RhH2(η1-S-BT)2(PPh3)2]+ which evolves into [Rh(π-BT) (PPh3)2]+, where BT is likely to be η5-bonded through the thiophene ring. Semiempirical (CNDO) theoretical calculations on the interactions of the fragment [Rh-(PH3)2]+ with BT revealed that both η5-bonding through the thiophene ring and η6-bonding through the benzene ring are possible; in the former case, the bonding is dominated by donation from a filled 5a′ BT orbital localized mainly on the S lone pair to empty 3a1 and 2b1 metal orbitals, whereas in the latter the main interaction is donation from a delocalized 4a′ BT orbital to an empty b2 metal orbital. The dihydride [Rh(BT)(H)2(PH3)2]+ which is formed by reaction of [(η5-BT)Rh(PH3)2]+ with H2 may contain BT coordinated η1-S, η2-C2=C3 or η4; [Rh(η4-BT)(H)2(PH3)2]+ was found to be more stable than [Rh(η1-BT)(H)2(PH3)2]+ and [Rh(η2-BT)- (H)2(PH3)2]+. The largest activation of the C=C bond of the thiophene moiety is produced by the η2 mode of bonding. All this information leads to a hydrogenation mechanism in which the active species is most probably the 18 electron π-bonded species [Rh(η5-BT)(PPh3)2]+, which is in equilibrium with an olefin-like complex [Rh(H)2(η2-BT) (PPh3)2]+. The rate determining step of the catalytic reaction is the transfer of hydrides from Rh to η2-BT, to yield [Rh(η1-SDHBT)(PPh3)2]+; subsequent rapid reaction with BT liberates the product and restarts the catalytic cycle. This mechanism provides a good model for understanding the initial hydrogenation step in the heterogeneous hydrodesulfurization of BT on solid catalysts.",

author = "S{\'a}nchez-Delgado, \{Roberto A.\} and Ver{\'o}nica Herrera and Luis Rinc{\'o}n and Antida Andriollo and Gonzalo Mart{\'i}n",

year = "1994",

month = feb,

day = "1",

doi = "10.1021/om00014a029",

language = "Ingl{\'e}s",

volume = "13",

pages = "553--561",

journal = "Organometallics",

issn = "0276-7333",

publisher = "American Chemical Society",

number = "2",

}

Sánchez-Delgado, RA, Herrera, V, Rincón, L, Andriollo, A & Martín, G 1994, 'Molecular Analogs of Surface Species. 3. The Mechanism of the Regioselective Homogeneous Hydrogenation of Benzothiophene by Use of [Rh(COD)(PPh₃)₂]PF₆ as the Catalyst Precursor. Kinetic and Theoretical Study', Organometallics, vol. 13, n.º 2, pp. 553-561. https://doi.org/10.1021/om00014a029

Molecular Analogs of Surface Species. 3. The Mechanism of the Regioselective Homogeneous Hydrogenation of Benzothiophene by Use of [Rh(COD)(PPh₃)₂]PF₆ as the Catalyst Precursor. Kinetic and Theoretical Study. / Sánchez-Delgado, Roberto A.; Herrera, Verónica; Rincón, Luis et al.
En: Organometallics, Vol. 13, N.º 2, 01.02.1994, p. 553-561.

Producción científica: Contribución a una revista › Artículo › revisión exhaustiva

TY - JOUR

T1 - Molecular Analogs of Surface Species. 3. The Mechanism of the Regioselective Homogeneous Hydrogenation of Benzothiophene by Use of [Rh(COD)(PPh3)2]PF6 as the Catalyst Precursor. Kinetic and Theoretical Study

AU - Sánchez-Delgado, Roberto A.

AU - Herrera, Verónica

AU - Rincón, Luis

AU - Andriollo, Antida

AU - Martín, Gonzalo

PY - 1994/2/1

Y1 - 1994/2/1

N2 - The mechanism of the regioselective hydrogenation of benzo[b]thiophene (BT) to 2,3- dihydrobenzo[b]thiophene (DHBT) in 2-methoxyethanol solution at 125 °C and ambient or subambient pressure of H2, using [Rh(COD)(PPh3)2]PF6 (1) (COD = 1,3-cyclooctadiene) as the catalyst precursor has been investigated by a combination of kinetic, chemical, and theoretical methods. The kinetic study led to a rate law ri= k7K6 [Rh]0[H2]/(1 + K6[H2]), where (kcat)exp = k7K6 = 0.726 M-1 s-1, k7 = 3.70 × 10-2 s-1, and K6 = 19.61 M-1. The calculated activation parameters are ΔH‡ = 20.1 ± 0.9 kcal/mol, ΔS‡ = −11.1 ± 0.8 eu, and ΔG‡ = 23 ± 3 kcal/mol. 1 probably reacts with hydrogen to produce an unstable intermediate [RhH2(η1-S-BT)2(PPh3)2]+ which evolves into [Rh(π-BT) (PPh3)2]+, where BT is likely to be η5-bonded through the thiophene ring. Semiempirical (CNDO) theoretical calculations on the interactions of the fragment [Rh-(PH3)2]+ with BT revealed that both η5-bonding through the thiophene ring and η6-bonding through the benzene ring are possible; in the former case, the bonding is dominated by donation from a filled 5a′ BT orbital localized mainly on the S lone pair to empty 3a1 and 2b1 metal orbitals, whereas in the latter the main interaction is donation from a delocalized 4a′ BT orbital to an empty b2 metal orbital. The dihydride [Rh(BT)(H)2(PH3)2]+ which is formed by reaction of [(η5-BT)Rh(PH3)2]+ with H2 may contain BT coordinated η1-S, η2-C2=C3 or η4; [Rh(η4-BT)(H)2(PH3)2]+ was found to be more stable than [Rh(η1-BT)(H)2(PH3)2]+ and [Rh(η2-BT)- (H)2(PH3)2]+. The largest activation of the C=C bond of the thiophene moiety is produced by the η2 mode of bonding. All this information leads to a hydrogenation mechanism in which the active species is most probably the 18 electron π-bonded species [Rh(η5-BT)(PPh3)2]+, which is in equilibrium with an olefin-like complex [Rh(H)2(η2-BT) (PPh3)2]+. The rate determining step of the catalytic reaction is the transfer of hydrides from Rh to η2-BT, to yield [Rh(η1-SDHBT)(PPh3)2]+; subsequent rapid reaction with BT liberates the product and restarts the catalytic cycle. This mechanism provides a good model for understanding the initial hydrogenation step in the heterogeneous hydrodesulfurization of BT on solid catalysts.

AB - The mechanism of the regioselective hydrogenation of benzo[b]thiophene (BT) to 2,3- dihydrobenzo[b]thiophene (DHBT) in 2-methoxyethanol solution at 125 °C and ambient or subambient pressure of H2, using [Rh(COD)(PPh3)2]PF6 (1) (COD = 1,3-cyclooctadiene) as the catalyst precursor has been investigated by a combination of kinetic, chemical, and theoretical methods. The kinetic study led to a rate law ri= k7K6 [Rh]0[H2]/(1 + K6[H2]), where (kcat)exp = k7K6 = 0.726 M-1 s-1, k7 = 3.70 × 10-2 s-1, and K6 = 19.61 M-1. The calculated activation parameters are ΔH‡ = 20.1 ± 0.9 kcal/mol, ΔS‡ = −11.1 ± 0.8 eu, and ΔG‡ = 23 ± 3 kcal/mol. 1 probably reacts with hydrogen to produce an unstable intermediate [RhH2(η1-S-BT)2(PPh3)2]+ which evolves into [Rh(π-BT) (PPh3)2]+, where BT is likely to be η5-bonded through the thiophene ring. Semiempirical (CNDO) theoretical calculations on the interactions of the fragment [Rh-(PH3)2]+ with BT revealed that both η5-bonding through the thiophene ring and η6-bonding through the benzene ring are possible; in the former case, the bonding is dominated by donation from a filled 5a′ BT orbital localized mainly on the S lone pair to empty 3a1 and 2b1 metal orbitals, whereas in the latter the main interaction is donation from a delocalized 4a′ BT orbital to an empty b2 metal orbital. The dihydride [Rh(BT)(H)2(PH3)2]+ which is formed by reaction of [(η5-BT)Rh(PH3)2]+ with H2 may contain BT coordinated η1-S, η2-C2=C3 or η4; [Rh(η4-BT)(H)2(PH3)2]+ was found to be more stable than [Rh(η1-BT)(H)2(PH3)2]+ and [Rh(η2-BT)- (H)2(PH3)2]+. The largest activation of the C=C bond of the thiophene moiety is produced by the η2 mode of bonding. All this information leads to a hydrogenation mechanism in which the active species is most probably the 18 electron π-bonded species [Rh(η5-BT)(PPh3)2]+, which is in equilibrium with an olefin-like complex [Rh(H)2(η2-BT) (PPh3)2]+. The rate determining step of the catalytic reaction is the transfer of hydrides from Rh to η2-BT, to yield [Rh(η1-SDHBT)(PPh3)2]+; subsequent rapid reaction with BT liberates the product and restarts the catalytic cycle. This mechanism provides a good model for understanding the initial hydrogenation step in the heterogeneous hydrodesulfurization of BT on solid catalysts.

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U2 - 10.1021/om00014a029

DO - 10.1021/om00014a029

M3 - Artículo

AN - SCOPUS:0000063697

SN - 0276-7333

VL - 13

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EP - 561

JO - Organometallics

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