Chemical Forums
Chemistry Forums for Students => Organic Chemistry Forum => Organic Chemistry Forum for Graduate Students and Professionals => Topic started by: Altered State on February 14, 2015, 09:58:46 AM
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I'm currently studying ferrocene metal-derivatives reactivity, but my limiting step is being always first metalathion process of ferrocene.
I tried to reproduce several conditions but with no success -always get products, but low yields-. In many papers is stated that the results are "sometimes not reproducible".
Do you know any reliable, recent procedure to perform a succesful lithiation of ferrocene and subsequent transmetallation?
My goal now is to get tributhyltin ferrocene in a decent yield. Any one knows of a procedure? The only ones I've found are really some old ones.
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I struggled with this procedure in grad school - never got a decent yield either. My go-to for monoderivatives of ferrocene is to acetylate then do normal carbonyl reactions to acetylferrocene. Vinylferrocene is easy to make from it. I know this doesn't directly help you - I'm posting in this thread because I'd be interested in any reliable procedure for making mono-derivatives of Fc - slight threadjack.
The one we use for acetylferrocene and vinylferrocene is from Synthetic Pages: http://cssp.chemspider.com/Article.aspx?id=759
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I would try using nBuLi and tetramethylethylene diamine as a chelation assister. That has worked for me in the past on ferrocene compounds.
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I would try using nBuLi and tetramethylethylene diamine as a chelation assister. That has worked for me in the past on ferrocene compounds.
That yields the dilithiated product, my goal is the monomotalathion... I only was able to get this product with tBuLi 0ºC or tBuLi + tBuOK at low temperature.
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Then I would try 1.1 eq of nBuLi, in THF, added cold, but then warm the solution up to RT before the next step, to ensure complete deprotonation, then re-cool it before the next step. That should provide the monoadduct. Look at the Japanese authored (Hayshi?) papers from the 1970-1980's for the best preps. Don't have my refs here.
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Exclusive preparation of monolithioferrocene actually posed quite a challange for some time, and a good comparison of conditions can be found in a 1996 paper from Sanders and Mueller-Westerhoff - "The lithiation of ferrocene and ruthenocene: a retraction and an improvement".
http://www.sciencedirect.com/science/article/pii/0022328X9505914B (http://www.sciencedirect.com/science/article/pii/0022328X9505914B)
From personal experience I would recommend the tBuLi-KOtBu system. Dropwise addition of tBuLi to ferrocene and KOtBu in THF at -78°C with rapid stirring (minimizing local heating), followed by stirring for 2 h can form monolithioferrocene in >90%. Then you can add your electrophile (portionwise). Raising the temperature, rapid addition of BuLi or too slow a stir rate increases the proportion of dilithioferrocene formed. For a recent example of this approach applied to halogenated ferrocenes, see the link below.
http://pubs.rsc.org/en/Content/ArticleLanding/2013/DT/c2dt32779a (http://pubs.rsc.org/en/Content/ArticleLanding/2013/DT/c2dt32779a)
To generate tributyltin ferrocene, an appropriate reagent would seem to be tributyltinchloride (link below)? This paper also has some good discussion on the effects of changing reaction conditions.
http://pubs.acs.org/doi/abs/10.1021/jo00113a033 (http://pubs.acs.org/doi/abs/10.1021/jo00113a033)
Hope that helps!