I have an aminoferrocene starting material and i am trying to lithiate it so i can add an aldehyde group on position 2. I am following a method in which they use n-butyllithium (1.1 equiv) with potassium tert-butoxide (0.1 equiv) stirring at room temperature for 16 hours in diether ether under argon and then adding dry dmf (3 equiv) and stirring for an additional 4 hours at room temperature. I have not been successful as no reaction seems to occur. Could someone assist with what i could possibly be doing wrong?
My diether ether, n-butyllithium, dmf and potassium tert-butoxide are all dry reagents purchased recently from sigma. So i am not sure if need to change my solvent to dry thf or perhaps use very low temperatures like -78 degrees?
One piece of advice I can give you is, use freshly distilled diethyl ether! Never from the bottle. And the generation of the carbanion should be at -78 degrees, right?
Good luck!
Dear Christina, many thanks for asking this very interesting technical question. Apparently your followed a literature procedure, right? Did you observe anything unusual which was not described in this procedure? The reaction temperature should be outlined in detail in the literature reference. So I'm wondering what made you suspect that something went wrong? The problem / characteristics of ferrocene chemistry is that the vast majority of ferrocene derivatives are more or less orange in color. My personal guess is that the reaction proceeded as planned and that you did nothing wrong. I assume that the addition of DMF has the purpose of solubilizing the lithiated ferrocene intermediate. In the end you will most likely have an orange solution which looks much the same as in the beginning of the reaction. Thus my suggestion would be to just proceed with the next step and tray to isolate your final product as described.
Good luck and best wishes, Frank Edelmann
Thank you Prof Frank T. Edelmann. Yes, I did follow a literature procedure (find attached). The reason I am sure the reaction is not working is because I have isolated the product and run NMR on it. According to the TLC, the starting material and reaction mixture both have the same rf values. The colour of the original starting material is yellow. The colour of the product from the reaction mixture is also yellow. And based on the NMR (proton and carbon), there is no aldehyde peak present.
To make sure, the deprotonation step works well, quench an aliquot in D2O and do a 13C. Deuterium coupling proves successful deprotonation.
Dear Christina, thank you for your kind response and explanation. Did you check the purity of your starting material? I assume you did. Also please have a look at the original references cited in your paper (Refs. [27] and [28]). In the old J. Am. Chem. Soc. paper from 1965 they use only n-butyllithium for the metalation reaction. We did this many times with dimethylaminomethylferrocene, and it should work in your case too. Here is the procedure:
Under an atmosphere of N2, 16 ml (25 mmol) of a 1.5 M solution of n-butyllithium in hexane was added dropwise over a period of 10 minutes to a stirred solution of 2.44 g (10 mmoles) of dimethylaminomethylferrocene in 10 ml. of anhydrous diethyl ether. The slightly exothermous metalation was completed by stirring for another 1 h and r.t. and the solution was then used directly for further reactions.
I hope this works. Good luck and best wishes, Frank Edelmann
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