Effects of Multiple Catalyst Deactivation Pathways and Continuous Ligand Recycling on the Kinetics of Pd-Catalyzed C-N Coupling Reactions

J Org Chem. 2019 Apr 19;84(8):4653-4660. doi: 10.1021/acs.joc.8b02214. Epub 2018 Oct 24.

Abstract

Unusual Pd deactivation and inhibition pathways were observed in a C-N coupling system. Irreversible catalyst deactivation involved C-H insertion of Pd into BippyPhos leading to an off-cycle palladaphosphacyclobutene. Product inhibition led to deactivated Pd but released ligand in the process, allowing it to react with additional Pd precursor to re-enter the catalytic cycle. In situ recycling of the ligand allowed for an input L/Pd ratio of ≪1 with no impact on reaction kinetics.