Introducing Type Ⅲ Metal Complex-Stabilized Olefin Radical Cation Induced Addition: A New Mechanism for Palladium-Catalyzed Wacker-Type Oxidation of Terminal Alkenes

To expand the substrate scope of the recently named “Radical Cation Induced Addition (RCIA)”, allowing functionalization of inactivated alkenes, the concept of “metal complex-stabilized olefin RCIA” as a type III RCIA is introduced here, with a rational design on the delocalization of radical spin the via metal-olefin interaction and through space interaction with other ligands. The feasibility of Pd-olefin radical cation complex via one-electron oxidation enabled by an oxidant is demonstrated in the Pd-catalyzed Wacker-type oxidation of terminal alkenes. The new mechanisms involved with “Pd(II) to Pd(I) catalytic cycle” matches the reported kinetic data of both the Wacker process and the Tsuji-Wacker oxidation of olefins to ketones and/or aldehydes, and it could explain the long-time unexplained phenomenon of a water nucleophilic attack onto a negatively charged π-olefin coordinated with Pd atom. Furthermore, with the new mechanisms, the stereochemistry of the debated syn/anti attack and the regioselective control in Tsuji-Wacker oxidation for either ketones or aldehydes would also be well explainable. A new concept of “on Pd through space interactions” is too proposed to explain the root of the anti-Markovnikov selectivity by the resulted “through space conjugation”. Implications in the rational design of recyclable Pd precatalysts with a water-soluble ligand for aldehyde selective Tsuji-Wacker oxidation of olefins with the concept of “in-situ surfactant”, and implications for the rational design of domino/one-pot reactions toward sustainable complex molecules with functionalities starting from olefins, by merging with organocatalysis, are also included.