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.
| Original language | English |
|---|---|
| Pages (from-to) | 4434-4436 |
| Number of pages | 3 |
| Journal | Inorganic Chemistry |
| Volume | 25 |
| Issue number | 24 |
| Publication status | Published - 1986 |
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- Inorganic Chemistry
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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 . / Philbin, Cecelia E.; Goldman, Alan S; Tyler, David R.
In: Inorganic Chemistry, Vol. 25, No. 24, 1986, p. 4434-4436.Research output: Contribution to journal › Article
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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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M3 - Article
VL - 25
SP - 4434
EP - 4436
JO - Inorganic Chemistry
JF - Inorganic Chemistry
SN - 0020-1669
IS - 24
ER -