From: Paul Handley (p.handley$##$chemistry.uq.edu.au)
Date: Sun Apr 09 2000 - 20:26:49 EDT
>>You might be able to generate it in situ, eg substrate + ZnCl2 in methanol,
>>add NaBH4 with stirring. I know this works for CoCl2/NaBH4 for >reducing
>>nitriles, nitros and amides, see Tet Lett. no. 52 p4555 1969
>You may know the function of CoCl2 in those reducing reactions? Since NaBH4
>self is a reducing agent,the role of CoCl2 is intriguing. Could you show me
>a rope on this?
>
>Y. Zhou
The reference above doesnt give any mechanistic information, but I have
another one: Selective reduction of mono- and disubstituted olefins by
sodium borohydride and cobalt(ii), Sung-Kee Chung, J.Org.Chem. 44 1014 1979.
Apparently alcoholic NaBH4 can react with CoCl2 to produce Co metal,
Co(BH4)2 or "complexed cobalt hydrides" depending on the reaction
conditions. One or more of these is going to be your active species that
reduces nitriles etc. Deuterium labelling suggests a cobalt hydride for
the reduction of alkenes.
The JOC paper gives a number of references on transition metals and
hydride, maybe some of these could answer your question.
Paul Handley
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