Polyketones, thermoplastic polymers, are formed by the copolymerisation of carbon monoxide and one or more alkenes (typically ethylene with propylene).  The process utilises a palladium(II) catalyst with a bidentate ligand like 2,2′-bipyridine or 1,10-phenanthroline (phen) with a non-coordinating BARF counterion, such as [(phen)Pd(CH)(CO)]BAr.  The preparation of the catalyst involves the reaction of a dimethyl palladium complex with Brookhart's acid in acetonitrile with loss of methane and the catalytic species is formed by uptake of carbon monoxide to displace acetonitrile.
:[(EtO)H]BAr   +   [(phen)Pd(CH)]   +   MeCN   →   [(phen)Pd(CH)(MeCN)]BAr   +   2 EtO   +   CH
:[(phen)Pd(CH)(MeCN)]BAr   +   CO   → [(phen)Pd(CH)(CO)]BAr   +   MeCN
The mechanism involves migratory insertion whereby the polymer chain is bound to the catalytic centre and grows by the sequential insertion of carbon monoxide and the alkene between the palladium atom and the existing chain.  Defects occur when insertions do not alternate &ndash; that is, a carbon monoxide insertion follows a carbon monoxide insertion or an alkene insertion follows an alkene insertion &ndash; these are highlighted in red in the figure below.  This catalyst produces a very low rate of defects due to the difference in Gibbs energy of activation of each insertion &ndash; the energy barrier to inserting an alkene immediately following an alkene insertion is  ~12 kJ mol higher than barrier to carbon monoxide insertion.  Use of monodentate phosphine ligands also leads to undesirable side-products but bidentate phosphine ligands like 1,3-bis(diphenylphosphino)propane have been used industrially.