I am trying to react a 2-br-aniline derivative ligand with 9,10-dihydro-9,10-diboraanthracene. My lab has done something similar before in this paper (Scheme 1): Article A Molecular Boroauride: A Donor-Acceptor Complex of Anionic Gold
The lithiation of the ligand seems to work fine, using tbuli or secbuli and then quenching with H2O results in the Br being replaced with hydrogen. But when we try to add the lithiated ligand slowly into the DBA soln (ligand in Et2O, DBA in 50/50 Et2O:Pentane) at -78C and let it stir overnight under N2, the resulting crude product only shows 1H peaks for the ligand, the mass spec matches the ligand, and there are no peaks on the 11B NMR.
It seems like something is happening to the DBA. Has anyone else ever had trouble lithiating br-aniline reagents? What would cause boron peaks to just vanish?
Dear Michael Olsen sorry to see that your very interesting chemical question has not yet received any expert answers. As an inorganic chemist I'm not really an expert in organic synthesis, but we have long-standing experience with a variety of organolithium reagents. You certainly know that the Br/Li exchange reaction is kinetically controlled (that's why you ran the reaction at –78 °C). When this reaction is carried out e.g. in diethyl ether or mixtures of diethyl ether and n-pentane the P-containing organolithium intermediate shoudl form a yellow precipitate. It might be worth a try to reverse the addition sequence and add the solution of your 9,10-DBA to this suspension to have the lithium reagent always in excess. No guarantee that this will work, but it's certainly worth a try.
Please also have a look at the following potentially useful literature reference in which an alternative synthesis of the P-containing phenyllithium derivative is outlined:
Metalation of phosphine imides with organolithium compounds
Article Metalation of phosphine imides with organolithium compounds
Unfortunately this paper has not yet been posted as public full text on RG, but you can certainly access it through your institution.
Good luck with your research work and best wishes, Frank Edelmann
Dear Michael, Take 2-bromo-derivative and add nBuLi at -78 deg C (if you have NHR group, add two equivalents of nBuLi and continue stirring for 2h, add now your chloro- or bromo-derivative at the same temperature and slowly let the4 solution to attain room temperatre and continue stirring for another 3 h. Quench the reaction with iPrOH to protonate N-if it is a secondary amine. Rest is typical follow-up. Need more information, please read our papers which discuss exclusively about lithiation of similar systems but with phosphorus ligands and it is very helpful for you:
Inorg. Chem. 2016,55,8514-8526, Chem.Commun. 2021,21,57,4835-4838, Inorg. Chem. 2022, 61, 857-868,
RSC Advances, 2018,8,25704-26718, Dalton Trans.2020,49, 3434-3449.
If there is a problem in downloading those papers from journal sites, let me know; I shall send it to you.
As always, Dr.Edelmann has given very valuable suggestions.
If it is just bromoaniline than, NH2 group has to be protected before further reaction with nBuLi.
All the very best
Balakrishna
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