Zwitterion-Induced Organic–Metal Hybrid Catalysis in Aerobic Oxidation

In many metal catalyses, the traditional
strategy of removing chloride
ions is to add silver salts via anion exchange to obtain highly active
catalysts. Herein, we reported an alternative strategy of removing
chloride anions from ruthenium trichloride using an organic [P+-N–] zwitterionic compound via multiple
hydrogen bond interactions. The resultant organic–metal hybrid
catalytic system has successfully been applied to the aerobic oxidation
of alcohols, tetrahydroquinolines, and indolines under mild conditions.
The performance of zwitterion is far superior to that of many other
common Lewis bases or Brønsted bases. Mechanistic studies revealed
that the zwitterion triggers the dissociation of chloride from ruthenium
trichloride via nonclassical hydrogen bond interaction. Preliminary
studies show that the zwitterion is applicable to catalytic transfer
semi-hydrogenation.