Blue light photocatalysis of carbazole-based conjugated microporous polymers: Aerobic hydroxylation of phenylboronic acids to phenols.

Aerobic hydroxylation of phenylboronic acids to phenols has attracted considerable attention but is exceedingly challenging due to the obstacle in the activation of oxygen (O 2). Here, two carbazole-based conjugated microporous polymers (CMPs), namely TCB-CMP and EFC-CMP, were fabricated through polymerization of 1,3,5-tri(9 H -carbazole-9-yl)benzene (TCB) and 9,9′-(9,9-diethyl-9 H -fluorene-2,7-diyl)bis(9 H -carbazole) (EFC), respectively. Gratifyingly, with N,N' -diisopropylethylamine (DIPEA) as the hole (h+) quencher, blue light photocatalysis of both carbazole-based CMPs could execute the aerobic hydroxylation of phenylboronic acids in ethanol (C 2 H 5 OH). Importantly, the EFC-CMP imparted superior photocatalytic activity to TCB-CMP due to the favorable reduction of O 2 to superoxide anion (O 2 •–) by electron (e–). Thereby, O 2 •– conducted the highly selective aerobic hydroxylation of phenylboronic acids. The aerobic hydroxylation of a wide range of phenylboronic acids to corresponding phenols was achieved with high yields. The work further demonstrates the feasibility of taming the oxidation potential of CMPs in producing delicate products like phenols. Blue light photocatalytic aerobic hydroxylation of phenylboronic acids to phenols has been completed promptly over carbazole-based conjugated microporous polymers. [Display omitted] • Two carbazole-based CMPs, namely TCB-CMP and EFC-CMP, are fabricated. • The e– from carbazole activates O 2 to O 2 •– to execute the aerobic hydroxylation. • Carbazole acts as Lewis base to close the distance with phenylboronic acids. • The superior photocatalytic activity of EFC-CMP is due to the favorable reduction of O 2. • The overoxidation of functionalized phenols is circumvented by h+ quenching. [ABSTRACT FROM AUTHOR]