Unusually slow photodissociation of CO from (η6-C 6H6)Cr(CO)3 (M= Cr or Mo): A time-resolved Infrared, Matrix Isolation, and DFT investigation

Mohammed A.H. Alamiry; Nicola M. Boyle; Christopher M. Brookes; Michael W. George; Long Conor; Peter Portius; Mary T. Pryce; Kate L. Ronayne; Xue Zhong Sun; Michael Towrie; Q. Vuong Khuong

doi:10.1021/om800925s

Unusually slow photodissociation of CO from (η⁶-C ₆H₆)Cr(CO)₃ (M= Cr or Mo): A time-resolved Infrared, Matrix Isolation, and DFT investigation

Mohammed A.H. Alamiry, Nicola M. Boyle, Christopher M. Brookes, Michael W. George, Long Conor, Peter Portius, Mary T. Pryce, Kate L. Ronayne, Xue Zhong Sun, Michael Towrie, Q. Vuong Khuong

Research output: Journal Publication › Article › peer-review

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Abstract

The photochemistry of η⁶-C₆H₆)M(CO) ₃ (M = Cr or Mo) is described. Photolysis with λexc. > 300 nm of (η⁶-C₆H₆)Cr(CO)₃ in low-temperature matrixes containing CO produced the CO-loss product, while lower energy photolysis (λEXC. > 400 nm) produced Cr(CO)₆. Pulsed photolysis (λexc. = 400 nm) of (η⁶-C ₆H₆)Cr(CO)₃ in n-heptane solution at room temperature produced an excited-state species (1966 and 1888 cm^-1) that decays over 150 ps to (η⁶-C₆H₆)Cr(CO) ₂(n-heptane) (70%) and (η⁶-C₆H ₆)Cr(CO)₆ (30%). Pulsed photolysis (λexc. = 266 nm) of (eta;⁶-C₆H₆)Cr(CO)₃ in n-heptane produced bands assigned to (η⁶-C₆H ₆)Cr(CO)₆(n-heptane) (1930 and 1870 cm^-1) within 1 ps. These bands increase with a rate identical to the rate of decay of the excited-state species and the rate of recovery of( η⁶-C ₆H₆)Cr(CO)₆. Photolysis of (η⁶- C₆H₆)Mo(CO)₃ at 400 nm produced an excited-state species (1996 and 1898 cm^-1) and traces of (η⁶-C₆H₆)Mo(CO)₂(n-heptane) within 1 ps. For the chromium system CO-loss can occur following excitation at both 400 and 266 nm via an avoided crossing of a MACT (metal-to-arene charge transfer) and MCCT/LF (metal-to-carbonyl charge transfer/ligand field) states. This leads to an unusually slow CO-loss following excitation with 400 nm light. Rapid CO-loss is observed following 266 nm excitation because of direct population of the MCCT/LF state. The quantum yield for CO-loss in the chromium system decreases with increasing excitation energy because of the competing population of a high-energy unreactive MACT state. For the molydenum system CO-loss is a minor process for 400 nm excitation, and an unreactive MACT state is evident from the TRIR spectra. A higher quantum yield for CO-loss is observed following 266 nm excitation through both direct population of the MCCT/LF state and production of a vibrationally excited reactive MACT state. This results in the quantum yield for CO-loss increasing with increasing excitation energy.

Original language	English
Pages (from-to)	1461-1468
Number of pages	8
Journal	Organometallics
Volume	28
Issue number	5
DOIs	https://doi.org/10.1021/om800925s
Publication status	Published - 9 Mar 2009
Externally published	Yes

ASJC Scopus subject areas

Physical and Theoretical Chemistry
Organic Chemistry
Inorganic Chemistry

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10.1021/om800925s

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Alamiry, M. A. H., Boyle, N. M., Brookes, C. M., George, M. W., Conor, L., Portius, P., Pryce, M. T., Ronayne, K. L., Sun, X. Z., Towrie, M., & Khuong, Q. V. (2009). Unusually slow photodissociation of CO from (η⁶-C ₆H₆)Cr(CO)₃ (M= Cr or Mo): A time-resolved Infrared, Matrix Isolation, and DFT investigation. Organometallics, 28(5), 1461-1468. https://doi.org/10.1021/om800925s

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title = "Unusually slow photodissociation of CO from (η6-C 6H6)Cr(CO)3 (M= Cr or Mo): A time-resolved Infrared, Matrix Isolation, and DFT investigation",

abstract = "The photochemistry of η6-C6H6)M(CO) 3 (M = Cr or Mo) is described. Photolysis with λexc. > 300 nm of (η6-C6H6)Cr(CO)3 in low-temperature matrixes containing CO produced the CO-loss product, while lower energy photolysis (λEXC. > 400 nm) produced Cr(CO)6. Pulsed photolysis (λexc. = 400 nm) of (η6-C 6H6)Cr(CO)3 in n-heptane solution at room temperature produced an excited-state species (1966 and 1888 cm-1) that decays over 150 ps to (η6-C6H6)Cr(CO) 2(n-heptane) (70%) and (η6-C6H 6)Cr(CO)6 (30%). Pulsed photolysis (λexc. = 266 nm) of (eta;6-C6H6)Cr(CO)3 in n-heptane produced bands assigned to (η6-C6H 6)Cr(CO)6(n-heptane) (1930 and 1870 cm-1) within 1 ps. These bands increase with a rate identical to the rate of decay of the excited-state species and the rate of recovery of( η6-C 6H6)Cr(CO)6. Photolysis of (η6- C6H6)Mo(CO)3 at 400 nm produced an excited-state species (1996 and 1898 cm-1) and traces of (η6-C6H6)Mo(CO)2(n-heptane) within 1 ps. For the chromium system CO-loss can occur following excitation at both 400 and 266 nm via an avoided crossing of a MACT (metal-to-arene charge transfer) and MCCT/LF (metal-to-carbonyl charge transfer/ligand field) states. This leads to an unusually slow CO-loss following excitation with 400 nm light. Rapid CO-loss is observed following 266 nm excitation because of direct population of the MCCT/LF state. The quantum yield for CO-loss in the chromium system decreases with increasing excitation energy because of the competing population of a high-energy unreactive MACT state. For the molydenum system CO-loss is a minor process for 400 nm excitation, and an unreactive MACT state is evident from the TRIR spectra. A higher quantum yield for CO-loss is observed following 266 nm excitation through both direct population of the MCCT/LF state and production of a vibrationally excited reactive MACT state. This results in the quantum yield for CO-loss increasing with increasing excitation energy.",

author = "Alamiry, {Mohammed A.H.} and Boyle, {Nicola M.} and Brookes, {Christopher M.} and George, {Michael W.} and Long Conor and Peter Portius and Pryce, {Mary T.} and Ronayne, {Kate L.} and Sun, {Xue Zhong} and Michael Towrie and Khuong, {Q. Vuong}",

year = "2009",

month = mar,

day = "9",

doi = "10.1021/om800925s",

language = "English",

volume = "28",

pages = "1461--1468",

journal = "Organometallics",

issn = "0276-7333",

publisher = "American Chemical Society",

number = "5",

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TY - JOUR

T1 - Unusually slow photodissociation of CO from (η6-C 6H6)Cr(CO)3 (M= Cr or Mo)

T2 - A time-resolved Infrared, Matrix Isolation, and DFT investigation

AU - Alamiry, Mohammed A.H.

AU - Boyle, Nicola M.

AU - Brookes, Christopher M.

AU - George, Michael W.

AU - Conor, Long

AU - Portius, Peter

AU - Pryce, Mary T.

AU - Ronayne, Kate L.

AU - Sun, Xue Zhong

AU - Towrie, Michael

AU - Khuong, Q. Vuong

PY - 2009/3/9

Y1 - 2009/3/9

N2 - The photochemistry of η6-C6H6)M(CO) 3 (M = Cr or Mo) is described. Photolysis with λexc. > 300 nm of (η6-C6H6)Cr(CO)3 in low-temperature matrixes containing CO produced the CO-loss product, while lower energy photolysis (λEXC. > 400 nm) produced Cr(CO)6. Pulsed photolysis (λexc. = 400 nm) of (η6-C 6H6)Cr(CO)3 in n-heptane solution at room temperature produced an excited-state species (1966 and 1888 cm-1) that decays over 150 ps to (η6-C6H6)Cr(CO) 2(n-heptane) (70%) and (η6-C6H 6)Cr(CO)6 (30%). Pulsed photolysis (λexc. = 266 nm) of (eta;6-C6H6)Cr(CO)3 in n-heptane produced bands assigned to (η6-C6H 6)Cr(CO)6(n-heptane) (1930 and 1870 cm-1) within 1 ps. These bands increase with a rate identical to the rate of decay of the excited-state species and the rate of recovery of( η6-C 6H6)Cr(CO)6. Photolysis of (η6- C6H6)Mo(CO)3 at 400 nm produced an excited-state species (1996 and 1898 cm-1) and traces of (η6-C6H6)Mo(CO)2(n-heptane) within 1 ps. For the chromium system CO-loss can occur following excitation at both 400 and 266 nm via an avoided crossing of a MACT (metal-to-arene charge transfer) and MCCT/LF (metal-to-carbonyl charge transfer/ligand field) states. This leads to an unusually slow CO-loss following excitation with 400 nm light. Rapid CO-loss is observed following 266 nm excitation because of direct population of the MCCT/LF state. The quantum yield for CO-loss in the chromium system decreases with increasing excitation energy because of the competing population of a high-energy unreactive MACT state. For the molydenum system CO-loss is a minor process for 400 nm excitation, and an unreactive MACT state is evident from the TRIR spectra. A higher quantum yield for CO-loss is observed following 266 nm excitation through both direct population of the MCCT/LF state and production of a vibrationally excited reactive MACT state. This results in the quantum yield for CO-loss increasing with increasing excitation energy.

AB - The photochemistry of η6-C6H6)M(CO) 3 (M = Cr or Mo) is described. Photolysis with λexc. > 300 nm of (η6-C6H6)Cr(CO)3 in low-temperature matrixes containing CO produced the CO-loss product, while lower energy photolysis (λEXC. > 400 nm) produced Cr(CO)6. Pulsed photolysis (λexc. = 400 nm) of (η6-C 6H6)Cr(CO)3 in n-heptane solution at room temperature produced an excited-state species (1966 and 1888 cm-1) that decays over 150 ps to (η6-C6H6)Cr(CO) 2(n-heptane) (70%) and (η6-C6H 6)Cr(CO)6 (30%). Pulsed photolysis (λexc. = 266 nm) of (eta;6-C6H6)Cr(CO)3 in n-heptane produced bands assigned to (η6-C6H 6)Cr(CO)6(n-heptane) (1930 and 1870 cm-1) within 1 ps. These bands increase with a rate identical to the rate of decay of the excited-state species and the rate of recovery of( η6-C 6H6)Cr(CO)6. Photolysis of (η6- C6H6)Mo(CO)3 at 400 nm produced an excited-state species (1996 and 1898 cm-1) and traces of (η6-C6H6)Mo(CO)2(n-heptane) within 1 ps. For the chromium system CO-loss can occur following excitation at both 400 and 266 nm via an avoided crossing of a MACT (metal-to-arene charge transfer) and MCCT/LF (metal-to-carbonyl charge transfer/ligand field) states. This leads to an unusually slow CO-loss following excitation with 400 nm light. Rapid CO-loss is observed following 266 nm excitation because of direct population of the MCCT/LF state. The quantum yield for CO-loss in the chromium system decreases with increasing excitation energy because of the competing population of a high-energy unreactive MACT state. For the molydenum system CO-loss is a minor process for 400 nm excitation, and an unreactive MACT state is evident from the TRIR spectra. A higher quantum yield for CO-loss is observed following 266 nm excitation through both direct population of the MCCT/LF state and production of a vibrationally excited reactive MACT state. This results in the quantum yield for CO-loss increasing with increasing excitation energy.

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U2 - 10.1021/om800925s

DO - 10.1021/om800925s

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SN - 0276-7333

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JO - Organometallics

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Unusually slow photodissociation of CO from (η⁶-C ₆H₆)Cr(CO)₃ (M= Cr or Mo): A time-resolved Infrared, Matrix Isolation, and DFT investigation

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