Cooperative Pd(0)/Rh(II) Dual Catalysis: Interceptive Capturing of π-Allyl Pd(II) Complexes with α-Imino Rh(II) Carbenoids

Extensive effort has been expended to utilize π-allyl palladium complexes as electrophilic allyl donor intermediates in cooperative dual catalysis, but their counteranions such as carboxylates and alkoxides are almost always discarded as waste. We have developed a cooperative Pd(0)/Rh(II) dual-catalysis system that utilizes both electrophilic allyl and nucleophilic counteranion functionalities inherent in the starting allylic substrates. In this cooperative catalysis, redox-compatible Pd(0) and Rh(II) catalysts selectively activate allylic substrates and N-sulfonyl-1,2,3-triazoles to generate π-allyl Pd(II) complexes and 1,3-ambivalent equivalent α-imino Rh(II) carbenoid intermediates, respectively. The counteranion of the π-allyl Pd(II) complex acts as a nucleophile transferring to the electrophilic carbenic carbon to form Pd/Rh-associated zwitterionic intermediates, in which the cationic palladium species may coordinate with both counteranion and imine nitrogen in the same plane, establishing the Z geometry of the products.