Proximity-Enabled Photochemical C-H Functionalization using a Covalent Organic Framework-Confined Fe-2 (IV)-& mu;-oxo Species in Water

Water has been recognized as an excellent solvent formaneuveringboth the catalytic activity and selectivity, especially in the caseof heterogeneous catalysis. However, maintaining the active catalyticspecies in their higher oxidation states (IV/V) while retaining thecatalytic activity and recyclability in water is an enormous challenge.Herein, we have developed a solution to this problem using covalentorganic frameworks (COFs) to immobilize the (Et4N)(2)[Fe-III(Cl)bTAML] molecules, taking advantage ofthe COF's morphology and surface charge. By using the visiblelight and [Co-III(NH3)(5)Cl]Cl-2 as a sacrificial electron acceptor within the COF, we have successfullygenerated and stabilized the [(bTAML)Fe-IV-O-Fe-IV(bTAML)](-) species in water. The COF backbonesimultaneously acts as a porous host and a photosensitizer. This isthe first time that the photochemically generated Fe-2 (IV)-& mu;-oxo radical cation species has demonstratedhigh catalytic activity with moderate to high yield for the selectiveoxidation of the unactivated C-H bonds, even in water. To enhancethe catalytic activity and achieve good recyclability, we have developeda TpDPP COF film by transforming the TpDPP COF nanospheres. We haveachieved the regio- and stereoselective functionalization of unactivatedC-H bonds of alkanes and alkenes (3 & DEG;:2 & DEG; = 102:1 foradamantane with the COF film), which is improbable in homogeneousconditions. The film exhibits C-H bond oxidation with highercatalytic yield (32-98%) and a higher degree of selectivity(cis/trans = 74:1; 3 & DEG;:2 & DEG;= 100:1 for cis-decalin).