Synthesis of a Doubly Boron-Doped Perylene through NHC-Borenium Hydroboration/C-H Borylation/Dehydrogenation

Reaction of an N-heterocyclic carbene (NHC)-borenium ion with 9,10-distyrylanthracene forms four B-C bonds through two selective, tandem hydroboration-electrophilic C-H borylations to yield an isolable, crystallographically characterizable polycyclic diborenium ion as its [NTf2](-) salt (1). Dehydrogenation of 1 with TEMPO radical followed by acidic workup yields a 3,9-diboraperylene as its corresponding borinic acid (2). This sequence can be performed in one pot to allow the facile, metal-free conversion of an alkene into a small molecule containing a boron-doped graphene substructure. Doubly boron-doped perylene 2 exhibits visible range absorbance and fluorescence in chloroform solution (phi=0.63) and undergoes two reversible one-electron reductions at moderate potentials of -1.30 and -1.64eV vs. ferrocenium/ferrocene in DMSO. Despite sterically accessible boron centers and facile electrochemical reductions, compound 2 is air-, moisture-, and silica gel-stable.