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.