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

Abstract

Extensive effort has been expended to utilize pi-allyl palladium complexes as electrophilic allyl donor intermediates in cooperative dual catalysis, but their counter anions 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, redoxcompatible Pd(0) and Rh(II) catalysts selectively activate allylic substrates and N-sulfonyl-1,2,3-triazoles to generate Jrallyl Pd(II) complexes and 1,3-ambivalent equivalent alpha-imino Rh(II) carbenoid intermediates, respectively. The counter anion of the pi-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.