Copolymerisation, catalytic cycle

However, this is not always the case. Excess of K - K has been found to occur during the initial stage of the copolymerisation when the cooligomer chain bound to the metal is still soluble and catalysis occurs in the homogeneous phase [36]. This may also occur when protonolysis involves H20 in place of MeOH, with formation of a Pd - OH+ species, which regenerates Pd - H+ by insertion of CO to Pd - COOH+ followed by C02 evolution. Thus in each catalytic cycle one molecule of CO is not incorporated into the polymer chain, but is consumed as C02 ... 

The most common alkenes employed in the Pd-catalysed synthesis of alternating polyketones are ethene, styrene, propene and cyclic alkenes such as norbomene and norbornadiene. Even though the mechanism does not vary substantially with the alkene, the reactions of the various co-monomers are here reported and commented on separately, starting with the ethene/CO copolymerisation, which is still the most studied process. As a general scheme, the proposed catalytic cycles are presented first, then the spectroscopic experiments that have allowed one to elucidate each single mechanistic step. 

Replacing MeOH with water does not significantly affect the catalytic cycle of copolymerisation, which involves the usual steps of insertion of ethene into... 

The chain transfer by protonolysis represents the predominant termination step in homogeneous ethene/CO copolymerisation, and involves the reaction between a propagating Pd-alkyl species and MeOH or adventitious water (Scheme 7.15a). As a result, the propagation is terminated with formation of a polymeric chain with a ketone-end group and Pd-OMe (or Pd-OH) species, which can re-enter the catalytic cycle by CO insertion. 

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