Hybrid cycloolefin ligands for palladium–olefin cooperative catalysis

Abstract

The engineering of molecular catalysts in homogeneous catalysis enables new catalytic modes, which leads to efficient synthetic transformations. In this regard, the design of ligands for transition metal catalysis has played a major role. In transition metal catalysed reactions, olefins can serve as steering ligands by tuning the electronic and steric nature of the metal centre. Here we report unstrained olefin ligands that bear a P or S coordination site for use in the Pd-catalysed Catellani reaction. This olefin ligand shows a covalent catalytic function and enables an efficient ipso,ortho-difunctionalization of iodoarenes. Mechanistic analysis reveals a reversible covalent bonding between the substrate and the cycloolefin unit of the ligand, which forms key organopalladium intermediates to enable a new reactivity. Our results demonstrate a design concept that employs hybrid cycloolefin ligands as a covalent catalytic module, which opens up possibilities for further cooperative catalysis with other transition metal–olefin hybrids. Taking inspiration from palladium–norbornene cooperative catalysis, Catellani-type reactions are now performed using a hybrid olefin ligand with a P or S coordination site. This olefin ligand enables efficient ipso,ortho-difunctionalization of iodoarenes. Mechanistic studies show the formation of organopalladium intermediates that comprise both the substrate and the hybrid olefin ligand.