Ion-Pair Hydrogen Atom Transfer Catalysis Enables Cr-Catalyzed Allylation of Ketones Using Hydrocarbon Alkenes.

We report a catalytic allylation of ketones using simple hydrocarbon alkenes, enabled by a synergistic system comprising chromocene and photo-activatable ion-pair hydrogen atom transfer (IP-HAT) catalysts derived from a thiophosphoryl imide and N-heteroaromatics. This catalyst system generates highly nucleophilic, electron-rich allylchromium(III) species directly from unactivated alkenes, demonstrating broad applicability to various ketones, including aromatic, aliphatic, and multifunctional ketones. The reaction proceeds under mild conditions with high functional group tolerance. The modular design of the IP-HAT catalysts allows precise tuning of redox potential and HAT activity, with the enhanced reduction potential of the reduced N-heteroaromatics catalyst playing a pivotal role in efficiently regenerating the electron-rich chromocene(II) catalyst.