Energetics of the reactions of (η6-C6H6)Cr(CO)3 with n-heptane, N2, and H2 studied by high-pressure photoacoustic calorimetry

Eoin F. Walsh; Michael W. George; Simon Goff; Sergei M. Nikiforov; Vladimir K. Popov; Xue Zhong Sun; Martyn Poliakoff

doi:10.1021/jp9621686

Energetics of the reactions of (η⁶-C₆H₆)Cr(CO)₃ with n-heptane, N₂, and H₂ studied by high-pressure photoacoustic calorimetry

Eoin F. Walsh, Michael W. George, Simon Goff, Sergei M. Nikiforov, Vladimir K. Popov, Xue Zhong Sun, Martyn Poliakoff

Research output: Journal Publication › Article › peer-review

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Abstract

The enthalpy changes associated with the photosubstitution of (η⁶-C₆H₆)Cr(CO)₃ by n-heptane, H₂, and N₂ have been measured by high-pressure photoacoustic calorimetry (PAC). The kinetics of the reaction of (η⁶-C₆H₆)Cr(CO)₃ to form (η⁶-C₆H₆)Cr(CO)₂L (L = H₂ and N₂) under high pressures of H₂ and N₂ have been monitored by time-resolved infrared spectroscopy (TRIR), showing that the increased concentration of ligand at high pressure greatly accelerates the reaction, making it possible to use the PAC technique to study these reactions. PAC experiments in n-heptane show the enthalpy change for the reaction of (η⁶-C₆H₆)Cr(CO)₃ + H₂ → (η⁶-C₆H₆)Cr(CO)₂(η ²-H₂) + CO to be +91 ± 4 kJ mol^-1. The PAC data indicate that the strength of the Cr-L bond in (η⁶-C₆H₆)Cr(CO)₂L (L = H₂ and N₂) is similar to that in the corresponding Cr(CO)₅L complexes. We estimate the Cr-H₂ bond dissociation enthalpy (BDE) in (η⁶-C₆H₆)Cr(CO)₂(η ²-H₂) to be 60 ± 4 kJ mol^-1 and the Cr-N₂ BDE to be 6 kJ mol^-1 stronger (66 ± 4 kJ mol^-1). The thermal equilibrium between (η⁶-C₆H₆)Cr(CO)₂(η ²-H₂) and (η⁶-C₆H₆)Cr(CO)₂(N²) was studied by FTIR in a polyethylene matrix pressurized with a mixture of H₂ and N₂ (130 bar). Conversion of (η⁶-C₆H₆)Cr(CO)₂(N₂) to (η⁶-C₆H₆)Cr-(CO)₂(η ²-H₂) was achieved by using a high pressure of H₂ at 22°C.

Original language	English
Pages (from-to)	19425-19429
Number of pages	5
Journal	Journal of Physical Chemistry
Volume	100
Issue number	50
DOIs	https://doi.org/10.1021/jp9621686
Publication status	Published - 12 Dec 1996
Externally published	Yes

ASJC Scopus subject areas

General Engineering
Physical and Theoretical Chemistry

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@article{61eb483843bf4a9d9fe34b5b4e7e9358,

title = "Energetics of the reactions of (η6-C6H6)Cr(CO)3 with n-heptane, N2, and H2 studied by high-pressure photoacoustic calorimetry",

abstract = "The enthalpy changes associated with the photosubstitution of (η6-C6H6)Cr(CO)3 by n-heptane, H2, and N2 have been measured by high-pressure photoacoustic calorimetry (PAC). The kinetics of the reaction of (η6-C6H6)Cr(CO)3 to form (η6-C6H6)Cr(CO)2L (L = H2 and N2) under high pressures of H2 and N2 have been monitored by time-resolved infrared spectroscopy (TRIR), showing that the increased concentration of ligand at high pressure greatly accelerates the reaction, making it possible to use the PAC technique to study these reactions. PAC experiments in n-heptane show the enthalpy change for the reaction of (η6-C6H6)Cr(CO)3 + H2 → (η6-C6H6)Cr(CO)2(η 2-H2) + CO to be +91 ± 4 kJ mol-1. The PAC data indicate that the strength of the Cr-L bond in (η6-C6H6)Cr(CO)2L (L = H2 and N2) is similar to that in the corresponding Cr(CO)5L complexes. We estimate the Cr-H2 bond dissociation enthalpy (BDE) in (η6-C6H6)Cr(CO)2(η 2-H2) to be 60 ± 4 kJ mol-1 and the Cr-N2 BDE to be 6 kJ mol-1 stronger (66 ± 4 kJ mol-1). The thermal equilibrium between (η6-C6H6)Cr(CO)2(η 2-H2) and (η6-C6H6)Cr(CO)2(N2) was studied by FTIR in a polyethylene matrix pressurized with a mixture of H2 and N2 (130 bar). Conversion of (η6-C6H6)Cr(CO)2(N2) to (η6-C6H6)Cr-(CO)2(η 2-H2) was achieved by using a high pressure of H2 at 22°C.",

author = "Walsh, {Eoin F.} and George, {Michael W.} and Simon Goff and Nikiforov, {Sergei M.} and Popov, {Vladimir K.} and Sun, {Xue Zhong} and Martyn Poliakoff",

year = "1996",

month = dec,

day = "12",

doi = "10.1021/jp9621686",

language = "English",

volume = "100",

pages = "19425--19429",

journal = "Journal of Physical Chemistry",

issn = "0022-3654",

publisher = "American Chemical Society",

number = "50",

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TY - JOUR

T1 - Energetics of the reactions of (η6-C6H6)Cr(CO)3 with n-heptane, N2, and H2 studied by high-pressure photoacoustic calorimetry

AU - Walsh, Eoin F.

AU - George, Michael W.

AU - Goff, Simon

AU - Nikiforov, Sergei M.

AU - Popov, Vladimir K.

AU - Sun, Xue Zhong

AU - Poliakoff, Martyn

PY - 1996/12/12

Y1 - 1996/12/12

N2 - The enthalpy changes associated with the photosubstitution of (η6-C6H6)Cr(CO)3 by n-heptane, H2, and N2 have been measured by high-pressure photoacoustic calorimetry (PAC). The kinetics of the reaction of (η6-C6H6)Cr(CO)3 to form (η6-C6H6)Cr(CO)2L (L = H2 and N2) under high pressures of H2 and N2 have been monitored by time-resolved infrared spectroscopy (TRIR), showing that the increased concentration of ligand at high pressure greatly accelerates the reaction, making it possible to use the PAC technique to study these reactions. PAC experiments in n-heptane show the enthalpy change for the reaction of (η6-C6H6)Cr(CO)3 + H2 → (η6-C6H6)Cr(CO)2(η 2-H2) + CO to be +91 ± 4 kJ mol-1. The PAC data indicate that the strength of the Cr-L bond in (η6-C6H6)Cr(CO)2L (L = H2 and N2) is similar to that in the corresponding Cr(CO)5L complexes. We estimate the Cr-H2 bond dissociation enthalpy (BDE) in (η6-C6H6)Cr(CO)2(η 2-H2) to be 60 ± 4 kJ mol-1 and the Cr-N2 BDE to be 6 kJ mol-1 stronger (66 ± 4 kJ mol-1). The thermal equilibrium between (η6-C6H6)Cr(CO)2(η 2-H2) and (η6-C6H6)Cr(CO)2(N2) was studied by FTIR in a polyethylene matrix pressurized with a mixture of H2 and N2 (130 bar). Conversion of (η6-C6H6)Cr(CO)2(N2) to (η6-C6H6)Cr-(CO)2(η 2-H2) was achieved by using a high pressure of H2 at 22°C.

AB - The enthalpy changes associated with the photosubstitution of (η6-C6H6)Cr(CO)3 by n-heptane, H2, and N2 have been measured by high-pressure photoacoustic calorimetry (PAC). The kinetics of the reaction of (η6-C6H6)Cr(CO)3 to form (η6-C6H6)Cr(CO)2L (L = H2 and N2) under high pressures of H2 and N2 have been monitored by time-resolved infrared spectroscopy (TRIR), showing that the increased concentration of ligand at high pressure greatly accelerates the reaction, making it possible to use the PAC technique to study these reactions. PAC experiments in n-heptane show the enthalpy change for the reaction of (η6-C6H6)Cr(CO)3 + H2 → (η6-C6H6)Cr(CO)2(η 2-H2) + CO to be +91 ± 4 kJ mol-1. The PAC data indicate that the strength of the Cr-L bond in (η6-C6H6)Cr(CO)2L (L = H2 and N2) is similar to that in the corresponding Cr(CO)5L complexes. We estimate the Cr-H2 bond dissociation enthalpy (BDE) in (η6-C6H6)Cr(CO)2(η 2-H2) to be 60 ± 4 kJ mol-1 and the Cr-N2 BDE to be 6 kJ mol-1 stronger (66 ± 4 kJ mol-1). The thermal equilibrium between (η6-C6H6)Cr(CO)2(η 2-H2) and (η6-C6H6)Cr(CO)2(N2) was studied by FTIR in a polyethylene matrix pressurized with a mixture of H2 and N2 (130 bar). Conversion of (η6-C6H6)Cr(CO)2(N2) to (η6-C6H6)Cr-(CO)2(η 2-H2) was achieved by using a high pressure of H2 at 22°C.

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U2 - 10.1021/jp9621686

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SN - 0022-3654

VL - 100

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JO - Journal of Physical Chemistry

JF - Journal of Physical Chemistry

IS - 50

ER -

Energetics of the reactions of (η⁶-C₆H₆)Cr(CO)₃ with n-heptane, N₂, and H₂ studied by high-pressure photoacoustic calorimetry

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