Re: ORGLIST:Nitro group compatibility by Negishi cross-coupling mediated by Nickel complexes

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From: Marko Hapke (marko.hapke$##$mail.uni-oldenburg.de)
Date: Mon Mar 03 2003 - 06:13:38 EST

Dear Peter,

indeed, nickel catalysts are not very compatible with nitro groups,
mainly because of the formation of nitroso metal-complexes. Another
point that could be stated, is that sometimes arylzinc compounds react
with the nitro groups itself. I made some experiments with
2-chloro-5-nitropyridine, using palladium-catalyzed Stille and Negishi
reaction, and in all cases the yield are low to extrem low (you can say:
not existing). Also the free amino compound could not be reacted with
arylzinc compounds in a adequate manner, even if the twofold amount of
the organozinc reagent was employed. Maybe it will be helpful, if you
reduce the nitro group (Fe/NH4Cl, NaBH4, or something else) and protect
the free amino group. The protected amine should be reacted in a
cross-coupling reaction more easily and even nickel catalysts should be
possible. We demonstrated that for the pyridine compound mentioned above
in a recently published paper (A. Lützen, M. Hapke, Eur. J. Org. Chem.
2002, 2292-2297).

Hope this helps

Marko

>Hi Dear Everybody!
>Please, did you hear about the Negishi cross-coupling reaction mediated by nickel complexes, where on the subtrate outgoing from aryl chlorides was nitro group attached? In JOC1997,42,1821-1823 it is stated, that nitro group destroys the catalytical activity of nickel complexes in cross-coupling reaction outgoing from arylchloride in reaction with arylzinkiumhalides. That is the reason, why palladium complexes are preferred to use instead of nickel complexes in the case, where nitro group is involved. In that article there was nothing about the yield of product when nickel-catalyst was used in the arylchloride cross-coupling reaction.
>So, I would very, very appreciate any information about the true. It must not be just Negishi cross-coupling reaction, i think the same effect could be observed also in the case of Suzuki, Stille etc cross-couplings, where nitro group is present withg nickel-catalyst .
>Myny Thanks!
>Peter
>
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