Carbon monoxide copolymerization with olefins

The first palladium-catalyzed copolymerization of carbon monoxide (CO) with olefins was described in 1982 [11], and as a consequence, carbonylative coupling reactions with alkenes were reported soon after. Notably, it was Negishi and Miller who discovered the first two examples of intramolecular carbonylative Heck reactions of 1-iodopenta-1,4-dienes by applying stoichiometric amounts of palladium [12]. 5-Methylenecyclopent-2-enones as the products were produced in moderate yields (Scheme 7.1). 

Polymerization mechanism for the a-olefin carbon monoxide copolymerization with chelating bis-phosphine... 

Palladium(II) complexes possessing bidentate ligands are known to efficiently catalyze the copolymerization of olefins with carbon monoxide to form polyketones.594-596 Sulfur dioxide is an attractive monomer for catalytic copolymerizations with olefins since S02, like CO, is known to undergo facile insertion reactions into a variety of transition metal-alkyl bonds. Indeed, Drent has patented alternating copolymerization of ethylene with S02 using various palladium(II) complexes.597 In 1998, Sen and coworkers also reported that [(dppp)PdMe(NCMe)]BF4 was an effective catalyst for the copolymerization of S02 with ethylene, propylene, and cyclopentene.598 There is a report of the insertion reactions of S02 into PdII-methyl bonds and the attempted spectroscopic detection of the copolymerization of ethylene and S02.599... 

The copolymerization of carbon monoxide and propylene confronts issues of both regiochemistry and stereochemistry. The catalyst must control the re osdectivity of the insertion of the a-olefin and the relative and absolute stereochemistry along the main chain. A majority of the studies on the copolymerization of carbon monoxide and substituted olefins have been conducted with styrene and propene as the olefin. The regiochemistiy and steieochemistiy of the copolymerization of carbon monoxide with styrene is distinct from those of the copolymerization of carbon monoxide with propene. These differences result finm differences in the electronic properties of tine olefins and its impact on the regiochemistry for the insertion. The copolymerization of carbon monoxide with styrene is presented first, and tine copolymerization of carbon monoxide with propylene is presented second. 

The copolymerization of carbon monoxide with styrene has been fine most stereoselective of the copolymerizations of carbon monoxide witfi substituted olefins, like file copolymerization of carbon monoxide with ethylene, fire copolymerization of carbon monoxide with styrene is perfectly alternating. Moreover, the regioselectivity for insertion of styrene is high. 

It has been shown by Barb and by Dainton and Ivin that a 1 1 complex formed from the unsaturated monomer (n-butene or styrene) and sulfur dioxide, and not the latter alone, figures as the comonomer reactant in vinyl monomer-sulfur dioxide polymerizations. Thus the copolymer composition may be interpreted by assuming that this complex copolymerizes with the olefin, or unsaturated monomer. The copolymerization of ethylene and carbon monoxide may similarly involve a 1 1 complex (Barb, 1953). 

The catalyst [Pd(Me-DUPHOS)(MeCN)2](BF4)2 was also effective in the alternating asymmetric copolymerization of aliphatic a-olefins with carbon monoxide [27,28]. The polymer synthesized in a CH3N02-CH30H mixture has both 1,4-ketone and spiroketal (10) units in the main chain. The propylene-CO copolymer consisting only of a 1,4-ketone structure shows [ ]D +22° (in (CF3)2CHOH), and the optical purity of the main chain chiral centers is over 90% as estimated by NMR analysis using a chiral Eu shift reagent. 

In addition to a-olefins, p-/-butylstyrene can be used as a comonomer for the isotactic specific copolymerization with carbon monoxide with chiral induction [32], Whereas bipyridyl as ligand gives a syndiotactic polymer, the Pd-catalyzed polymerization with ligand 11 leads to a polymer with isotacticity of over 98% and high optical activity ([ ]D -536° (in CH2C12)) [33, 34]. The BINAPHOS catalyst described above is also effective in this type of copolymerization [25],... 

Drent, E., van Broekhoven, J. A. M., Doyle, M. J. and Wong, P. K., Palladium Catalyzed Copolymerization of Carbon Monoxide with Olefins to Alternating Polyketones and Polyspiroketals , in Ziegler Catalysts, Springer-Verlag, Berlin, 1995, pp. 481 196. 

Semiyen, J. A. Ring-Chain Equilibria and the Conformations of Polymer Chains. Vol. 21, pp. 41-75. Sen, A. The Copolymerization of Carbon Monoxide with Olefins. Vol. Tip4, pp. 125-144. 

Palladium complexes figure prominently as well in the copolymerization of Q -olefins with carbon monoxide. Unlike the low molecular weight photodegradable random copolymers of ethylene and CO produced from a free-radical process, olefin/carbon monoxide copolymers produced from homogeneous palladium catalysts are perfectly alternating, the result of successive insertions of olefin and CO (Figure 19). Consecutive insertion of two similar monomers is either slow... 

In this more interesting case, each monomer adds only to an end unit of the other kind (k = 0, km - 0). In the polymer, units MA and M then alternate. Coordination copolymerization of olefins and carbon monoxide, catalyzed by complex hydrides of Pd(II) or Rh(I) in the presence of an alcohol co-solvent to yield polyketo esters, provides an example [133,134] Olefin and carbon monoxide are added altematingly, and reaction with alcohol terminates the kinetic chain and restores the catalyst. For ethene as the olefin ... 

This is the case, for example, in the copolymerization of carbon monoxide and ethylene where the CO will not add to itself but does copolymerize with the olefin monomer. General theoretical treatments have been developed for such cases, taking into account temperature and penultimate effects. Again, the superiority of these more complicated theories over the simpler copolymer model is not proved for all systems to which they have been applied. 

---