Tuning band structures of Hf-PCN-224(M) for β-Carbonyl C(sp3)-H bond activation and difunctionalization: Tandem C(sp3) radical cross-coupling through photoredox

Abstract

The construction of C(sp3)-C(sp3) bonds by different C(sp3) radicals coupling reactions is still unexplored due to the high bond dissociation energy of C(sp3)-H bond and the difficulty for selective generating of C(sp3) radical. Benefiting from the precisely regulating for band structures of Hf-PCN-224(M), the β-carbonyl C(sp3)-H bonds are effectively oxidized by photo-generated holes to affording C(sp3) radicals in this work. C(sp3)-C(sp3) and C(sp3)-O bonds are constructed by tandem radical-radical cross-coupling, hydrogen atom transfer (HAT), and radical-radical cross-coupling between two C(sp3)-H bonds, enabling an effective C3-difunctionalization of indolin-2-ones under photo-thermo synergetic catalysis on Hf-PCN-224(Cu). Significantly, OH serves as triple roles: introduced hydroxyl group in situ, HAT abstractor and α-heteroatom for secondary activating C(sp3)-H bonds. Control experiments, EPR spectroscopy and DFT calculation provide insight into the tandem radicals cross-coupling mechanism. This operable strategy opens up a door for the difunctionalization of C(sp3)-H bonds in heterogeneous photoredox manner.