Back-reactions in the photochemical disproportionation of Cp2Mo2(CO)6 (Cp = C5H4CH3) and the wavelength-dependent photochemistry of the Cp2Mo2(CO)6 complex with PPh3

Cecelia E. Philbin, Alan S Goldman, David R. Tyler

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Abstract

Irradiation (λ > 525 nm) of Cp2Mo2(CO)6 (Cp = η5-C5H5, η5-C5H4CH3) with PPh3 in CH2Cl2 proceeds as follows: Cp2Mo2(CO)6 + PPh3hv CpMo(CO)3PPh3 + + CpMo(CO)3 -. A similar disproportionation reaction does not occur in benzene or other nonpolar solvents for λ > 525 nm but does occur for λ = 290 nm. (The cationic product in this case is CpMo(CO)2(PPh3)2 +.) The dependence of the disproportionation reaction on solvent and radiation wavelength is shown to be a consequence of a facile back-reaction: CpMo(CO)3PPh3 + + CpMo(CO)3 - → Cp2Mo2(CO)6 + PPh3. Thus, irradiation of Cp2Mo2(CO)6 with PPh3 at 525 nm in nonpolar solvents does disproportionate the dimer but the back-reaction occurs and there is no net disproportionation. The back-reaction is considerably slower in CH2Cl2, and net disproportionation is therefore observed in this solvent. Net disproportionation does occur at 290 nm in benzene because a secondary photochemical reaction of the initially formed CpMo-(CO)3PPh3 + product occurs: CpMo(CO)3PPh3 + + PPh3hv CpMo(CO)2(PPh3)2 +; this disubstituted cation and CpMo(CO)3 - do not back-react. Several other unexplained observations from our previous studies of the disproportionation reactions can also be interpreted in terms of the occurrence of a back-reaction. The back-reactions can be prevented in several ways: a more polar solvent can be used; the cationic or anionic products can be reacted further; the disproportionation reaction can be done at low temperature. Each of these methods is discussed and demonstrated.

Original languageEnglish
Pages (from-to)4434-4436
Number of pages3
JournalInorganic Chemistry
Volume25
Issue number24
Publication statusPublished - 1986

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Photochemical reactions
photochemical reactions
Wavelength
wavelengths
Benzene
Irradiation
Dimers
Cations
products
benzene
irradiation
Radiation
dimers
occurrences
cations
Temperature
radiation

ASJC Scopus subject areas

  • Inorganic Chemistry

Cite this

@article{0cd75b35617340a783770855787e6870,
title = "Back-reactions in the photochemical disproportionation of Cp2Mo2(CO)6 (Cp = C5H4CH3) and the wavelength-dependent photochemistry of the Cp2Mo2(CO)6 complex with PPh3",
abstract = "Irradiation (λ > 525 nm) of Cp2Mo2(CO)6 (Cp = η5-C5H5, η5-C5H4CH3) with PPh3 in CH2Cl2 proceeds as follows: Cp2Mo2(CO)6 + PPh3 →hv CpMo(CO)3PPh3 + + CpMo(CO)3 -. A similar disproportionation reaction does not occur in benzene or other nonpolar solvents for λ > 525 nm but does occur for λ = 290 nm. (The cationic product in this case is CpMo(CO)2(PPh3)2 +.) The dependence of the disproportionation reaction on solvent and radiation wavelength is shown to be a consequence of a facile back-reaction: CpMo(CO)3PPh3 + + CpMo(CO)3 - → Cp2Mo2(CO)6 + PPh3. Thus, irradiation of Cp2Mo2(CO)6 with PPh3 at 525 nm in nonpolar solvents does disproportionate the dimer but the back-reaction occurs and there is no net disproportionation. The back-reaction is considerably slower in CH2Cl2, and net disproportionation is therefore observed in this solvent. Net disproportionation does occur at 290 nm in benzene because a secondary photochemical reaction of the initially formed CpMo-(CO)3PPh3 + product occurs: CpMo(CO)3PPh3 + + PPh3 →hv CpMo(CO)2(PPh3)2 +; this disubstituted cation and CpMo(CO)3 - do not back-react. Several other unexplained observations from our previous studies of the disproportionation reactions can also be interpreted in terms of the occurrence of a back-reaction. The back-reactions can be prevented in several ways: a more polar solvent can be used; the cationic or anionic products can be reacted further; the disproportionation reaction can be done at low temperature. Each of these methods is discussed and demonstrated.",
author = "Philbin, {Cecelia E.} and Goldman, {Alan S} and Tyler, {David R.}",
year = "1986",
language = "English",
volume = "25",
pages = "4434--4436",
journal = "Inorganic Chemistry",
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TY - JOUR

T1 - Back-reactions in the photochemical disproportionation of Cp2Mo2(CO)6 (Cp = C5H4CH3) and the wavelength-dependent photochemistry of the Cp2Mo2(CO)6 complex with PPh3

AU - Philbin, Cecelia E.

AU - Goldman, Alan S

AU - Tyler, David R.

PY - 1986

Y1 - 1986

N2 - Irradiation (λ > 525 nm) of Cp2Mo2(CO)6 (Cp = η5-C5H5, η5-C5H4CH3) with PPh3 in CH2Cl2 proceeds as follows: Cp2Mo2(CO)6 + PPh3 →hv CpMo(CO)3PPh3 + + CpMo(CO)3 -. A similar disproportionation reaction does not occur in benzene or other nonpolar solvents for λ > 525 nm but does occur for λ = 290 nm. (The cationic product in this case is CpMo(CO)2(PPh3)2 +.) The dependence of the disproportionation reaction on solvent and radiation wavelength is shown to be a consequence of a facile back-reaction: CpMo(CO)3PPh3 + + CpMo(CO)3 - → Cp2Mo2(CO)6 + PPh3. Thus, irradiation of Cp2Mo2(CO)6 with PPh3 at 525 nm in nonpolar solvents does disproportionate the dimer but the back-reaction occurs and there is no net disproportionation. The back-reaction is considerably slower in CH2Cl2, and net disproportionation is therefore observed in this solvent. Net disproportionation does occur at 290 nm in benzene because a secondary photochemical reaction of the initially formed CpMo-(CO)3PPh3 + product occurs: CpMo(CO)3PPh3 + + PPh3 →hv CpMo(CO)2(PPh3)2 +; this disubstituted cation and CpMo(CO)3 - do not back-react. Several other unexplained observations from our previous studies of the disproportionation reactions can also be interpreted in terms of the occurrence of a back-reaction. The back-reactions can be prevented in several ways: a more polar solvent can be used; the cationic or anionic products can be reacted further; the disproportionation reaction can be done at low temperature. Each of these methods is discussed and demonstrated.

AB - Irradiation (λ > 525 nm) of Cp2Mo2(CO)6 (Cp = η5-C5H5, η5-C5H4CH3) with PPh3 in CH2Cl2 proceeds as follows: Cp2Mo2(CO)6 + PPh3 →hv CpMo(CO)3PPh3 + + CpMo(CO)3 -. A similar disproportionation reaction does not occur in benzene or other nonpolar solvents for λ > 525 nm but does occur for λ = 290 nm. (The cationic product in this case is CpMo(CO)2(PPh3)2 +.) The dependence of the disproportionation reaction on solvent and radiation wavelength is shown to be a consequence of a facile back-reaction: CpMo(CO)3PPh3 + + CpMo(CO)3 - → Cp2Mo2(CO)6 + PPh3. Thus, irradiation of Cp2Mo2(CO)6 with PPh3 at 525 nm in nonpolar solvents does disproportionate the dimer but the back-reaction occurs and there is no net disproportionation. The back-reaction is considerably slower in CH2Cl2, and net disproportionation is therefore observed in this solvent. Net disproportionation does occur at 290 nm in benzene because a secondary photochemical reaction of the initially formed CpMo-(CO)3PPh3 + product occurs: CpMo(CO)3PPh3 + + PPh3 →hv CpMo(CO)2(PPh3)2 +; this disubstituted cation and CpMo(CO)3 - do not back-react. Several other unexplained observations from our previous studies of the disproportionation reactions can also be interpreted in terms of the occurrence of a back-reaction. The back-reactions can be prevented in several ways: a more polar solvent can be used; the cationic or anionic products can be reacted further; the disproportionation reaction can be done at low temperature. Each of these methods is discussed and demonstrated.

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VL - 25

SP - 4434

EP - 4436

JO - Inorganic Chemistry

JF - Inorganic Chemistry

SN - 0020-1669

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