The NNaNMgNNaNMg cycle

03 July 2010 - Chemical misadventures

THF Mg kennedy 2010  In a previous episode Kennedy & Mulvey successfully isolated the sedated anion of THF as a zincate that was stabilized by both TMP and TMEDA. The potential of this unual compound containing a OCZnNNa cycle was then demonstrated in reactions with common electrophiles. Replacing zinc by magnesium in this procedure should be an easy walk in the park but it did not work out that way (DOI). Whereas sedated THF took 2 weeks to form in the zinc reaction pot, the magnesium version only took 5 minutes to form crystals. Two sets of crystals in fact. Turns out that THF is completely shredded to pieces. The first set of crystals belongs to dimagnesiated butadiene stabilized by TMP, sodium and TMEDA. In the second set of crystals magnesium, sodium and nitrogen form an inverted crown ether for the oxygen dianion originally belonging to THF as well. In terms of a mechanism Mulvey cautiously offers THF deprotonation twice over forming the oxide and a dicarbene.