Communication
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Scheme 6 Stoichiometric defluorination of 14 by 3a.
for the hydrodehalogenation of geminal dichlorides: in a first
step the nickel(I) complex activates the geminal difluorocyclo-
propane 4a–11a by homolytic C–F cleavage and subsequent
ring-opening20 liberating the monofluoroallylic radical species
13 which may be either metal-stabilized or dissociated (Scheme 5).
The latter is transformed to the corresponding fluoroalkene
4b–11b via hydrogen atom abstraction from the nickel hydrido
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To further support the mechanistic proposal in which a C–F
bond is activated by the nickel(I) species in the initial step of
the catalytic cycle, we probed to see whether non-constrained
geminal fluorides would be disposed to defluorination under
these conditions. Indeed, the reaction of perfluorinated decalin
14 with 10 equiv. of the isolated nickel(I) species at room
temperature led to the quantitative formation of perfluorinated
naphthalene 15 as well as the nickel fluorido complex 1a
(Scheme 6). The formation of the unsaturated compound
during this reaction reflects the general reactivity pattern
observed for the dehalogenation of dihalogenated alkanes by
Ni(I) (TMC) complexes21 and, therefore, supports the proposed
occurrence of radical intermediates in the defluorination reac-
tion of difluorocyclopropanes presented in this work.
The results of this work demonstrate that the previously
developed nickel(I/II) system, which was found to be catalytically
active for the hydrodechlorination and -bromination of corres-
ponding geminal dihalides is also capable of activating the
geminal difluorocyclopropanes. The products, most probably
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We thank Alexander Ahrens and Steffen Ott for experi-
mental support. We acknowledge funding by the Deutsche
Forschungsgemeinschaft (Ga 488/9-1) as well as the University
of Heidelberg.
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Notes and references
‡ The product 1,1-diphenylallene was synthesized separately according
to literature procedure (Doering–LaFlamme allene synthesis) to verify
its formation during the reaction.22
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