Alternating copolymerization of alkenes and carbon monoxide catalyzed by cationic palladium complexes

In the late 1940s,Reppediscovered a nickel catalyst for the co‐oligomerization of ethene and carbon monoxide. Since then, various groups have made attempts to develop more efficient catalysts for this reaction. The recent discovery of a new class of very active palladium catalysts now allows, for the first time, ready access to a large variety of high‐molecular‐weight alkene/carbon‐monoxide co‐ and terpolymers. The catalysts comprise acis‐coordinated palladium(II) species associated with weakly or non‐coordinating anions. Their discovery has made it possible to develop a viable process for the commercial production of the first members of the new family of CARILON‐olefin/carbon monoxide copolymers. In this brief review, we highlight some key phenomena in polyketone catalysis. The elementary reaction steps in the palladium‐catalyzed polyketone formation during chain propagation, initiation and termination are outlined. The role of bidentate ligands and the reasons for perfect alternation in polymer chain growth are dicussed. The attractive feature of the catalysts, that they also catalyze the co‐ and terpolymerization of olefins higher than ethene with carbon monoxide, is briefly noted. A parallel between polyketone catalysis by cationic palladium complexes and modern polyolefin catalysis by cationic metallocene complexes is suggested.