Journal
ADVANCED SYNTHESIS & CATALYSIS
Volume 358, Issue 18, Pages 2949-2961Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/adsc.201600501
Keywords
benzophenone; copper; perfluoroalkylations; radical reactions; synthetic methods
Categories
Funding
- Agence Nationale de la Recherche (PET-Cat project) [ANR-13-BS07-0006-01]
- FOSET (project) [ANR-12-BS08-0007-01]
- University of Bordeaux
- CNRS
- Region Aquitaine
- Agence Nationale de la Recherche (ANR) [ANR-12-BS08-0007, ANR-13-BS07-0006] Funding Source: Agence Nationale de la Recherche (ANR)
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Iodoperfluooralkylation of terminal alkenes and alkynes is effectively photo-promoted by benzophenone 2 (BP) or the photoreducible copper(II) complex 1. In particular, BP at 1mol% in methanol upon 365nm irradiation with a low-pressure mercury lamp (type TLC=thin layer chromatography, 6W) results in a fast reaction with excellent reaction yields. Complex 1 and BP 2 exhibited very similar reactivity, suggesting that the reactions involving 1 are likely to be governed by the benzophenone photoactivation processes, rather than copper(I)/(II) redox processes. Mechanistic investigations using transient absorption spectroscopy revealed that a deactivation pathway of the benzophenone triplet ((BP)-B-3*) is via its reaction with the methanol solvent. We propose that the generated radicals, in particular (CH2OH)-C-., play a key role in the initiation step forming R-f(.) by reacting with RfI, R-f(.) then entering a radical chain cycle. (HNMR)-H-1 studies provided evidence that a substantial amount (approximate to 7% NMR yield) of the hemiacetal CH3OCH2OH is formed, i.e., the possible by-product of the reaction between (CH2OH)-C-. and RfI. Finally, DFT calculations indicate that a triplet-triplet energy transfer (TTET) process from (BP)-B-3* to perfluorooctyl iodide (C8F17I) is unlikely or should be rather slow under the reaction conditions, consistent with the transient absorption studies.
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