Novel diradical

15 February 2014 - Orgo

triplet diradical Yuan Li  Yuan Lu et al. describe here a novel diradical compound. Synthetic details: 2-mesitylmagnesium bromide Grignard reaction to dialdehyde 1, Friedel-Crafts reaction with boron trifluoride on diol 2 to hydrocarbon 3 and then deprotonation with lithium diisopropylamide to the dianion (green THF solution at -78°C) and then oxidation with iodine to the diradical product (orange-yellow 2-MeTHF solution at -78°C). Strategies that failed: direct oxidation by p-chloranil at RT resulted in a mess (but suggests the researchers were expecting a RT-stable diradical?), same oxidation at -78° was too slow. n-Butyl lithium in the deprotonation step resulted in butyl groups added.

ESR data of the successful reaction product suggest the diradical is predominantly a triplet species. It is persistent at -70°C for at least 24 hours, partly thanks to the two mesityl groups serving as kinetic shields. At room-temperature the diradical had rearranged to a 'dihydro compound' that was not investigated beyond mass spectroscopy.