Spontaneous resolution versus formation of racemic crystals of indenylpotassium complexes

Journal article, 2013

During a study of stereochemically labile organometallic reagents, we found that crystallisation of [K(ind)(pmdta)](n) (ind = indenyl, pmdta = N,N,N',N '',N ''-pentamethyldiethylenetriamine) from tetrahydrofuran (THF) gave rise to three different crystalline phases depending on the concentration. The more concentrated solutions gave racemic crystals of the previously known coordination polymer [K(ind)(pmdta)](n), alpha-1. More dilute solutions gave crystals of a new phase, beta-1, which was found to undergo spontaneous resolution. From even more dilute solutions, we were able to isolate a chiral inclusion compound with THF, 2, which also undergoes spontaneous resolution. Crystals of beta-1 and 2 were enantiomerically pure, and since beta-1 is a reactive organometallic reagent, attempts were made to use the crystals in enantioselective synthesis. Reacting single crystals with N-chlorosuccinimide gave rise to chiral 1-chloroindene, but no enantiomeric excess was observed.