Carbon alternating copolymerization with olefins

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... 

Since the aforementioned investigations, significant advances in aqueous catalytic insertion polymerization have only been made over the past decade. Alternating copolymerization of olefins with carbon monoxide, polymerization of ethylene and 1-olefins, and polymerizations of norbomenes and of butadiene have been studied. 

The paUadium( 11)-catalyzed alternating copolymerization of olefins with carbon monoxide is, by now, well documented [3]. The usual catalyst employed is a cat-... 

Sen, A. Mechanistic aspects of metal-catalyzed alternating copolymerization of olefins with carbon monoxide. Acc. Chem. Res. 1993, 26, 303-310. 

Benedetto, Macromol. Symp., 1995, 89, 443—454. Re-gio- and Stereocontrol in the Alternating Copolymerization of Olefins with Carbon Monoxide. 

Derivatives of polyphenylene vinylene are formed in the Pd-catalyzed reaction of ethylene with substituted dihalogeno arenes. This requires a change of the valence of the metal. In contrast to this the alternating copolymerization of olefins with carbon monoxide and the vinylic polymerization of norbomene is successful only if the two vsdent state of Pd is maintained. The mechanism of the Heck reaction (7) (equation 4) shows the limiting requirements to tune the reaction in one or the other way. 

Pd-complexes described for the alternating copolymerization of olefins with carbon monoxide shows similar characteristics non- or low coordinating anions as well as two ligand sites occupied by nitril. The p-H-elimination is a relatively fast reaction... 

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. 

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 ... 

Polymerization of 7V-vinylcarbazole catalyzed by dimethylglyoxime complexes of different metals immobilized on PVC follows the cationic mechanism. Lewis acids immobilized in a volume of swollen polymer gel catalyze cationic polymerization and oligomerization of vinyl ethers, etc. Cationic complexes of Pd(II) bound to modified PS initiate alternative copolymerization of fluorinated olefins (C F2 +i)(CH2)mCH=CH2 with carbon monoxide [112,113]. The product thus obtained was polyspiroketal rather than polyketone. 

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. 

Drent, E. vanBroekhoven, J.A.M. Doyle, M. J. Efficient palladium catalysts for the copolymerization of carbon monoxide with olefins to produce perfectly alternating polyketones. J. Organomet. Chem. 1991,477,235-251. 

Barsacchi, M. Batistini, A. Consiglio, G Suter, U. W. Stereochemislry of alternating copolymerization of vinyl olefins with carbon monoxide. Macmmolecules 1992,25,3604—3606. 

Jaing, Z. Adams, S. E. Sen, A. Stereo- and enantioselective alternating copolymerization of a-olefins with carbon monoxide. Macromolecules 1994, 27, 2694—2700. 

Jiang, Z. Sen, A. PaUadium(II)-catalyzed isospecific alternating copolymerization of aliphatic a-olefins with carbon monoxide and isospecific alternating coohgomerization of 1,2-disubstituted olefin with carbon monoxide. Synthesis of novel, optically active, isotactic 1,4- and 1,5-polyketones. J. Am. Chem. Soc. 1995,117,4455 67. 

Batistini, A. Consiglio, G Mechanistic aspects of the alternating copolymerization of carbon monoxide with olefins catalyzed by cationic palladium complexes. Organometallics 1992,11,1766-1769. 

Brookhart first reported the asymmetric alternating copolymerization of 4-tert-butylstyrene with carbon monoxide using [Pd(Me)(MeCN)(biox)][B(3,5-(CF3)2C6H3)4] (Figure 9). In this copolymerization, the enantioface of the olefin was selected by the chiral ligand instead of the chain end as a result, the polymer was completely isotactic. Since one enantioface was... 

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. 

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... 

Chain propagation of CO/ethylene copolymerization proceeds by a strictly alternating insertion of CO and olefin monomers in the growing chain. It is safe to assume that double CO insertion does not occur for thermodynamic reasons [Ic]. However, the complete absence of double ethylene insertions is remarkable because ethylene insertion in a Pd-alkyl species must be exothermic by about 20 kcal/mol (84 kJ mol). The observation of strict alternation is the more surprising since the same palladium catalysts also efficiently dimerize ethylene to butenes [25]. The perfect alternation is maintained even in the presence of very low concentrations of carbon monoxide. When starting abatch polymerization at a high ethylene/CO ratio, error-free copolymer is produced until all the CO is consumed then the system starts forming butenes (with some catalyst systems at about twice the rate of copolymerization ). 

The copolymerization of alkenes with carbon monoxide has attracted the attention of chemists for many years [1]. Following the commerciahzation of Carilon, an alternating olefin carbon monoxide terpolymer based on ethene and small amounts (5-10%) of propene (Scheme 8.1, 1), by Shell [2, 3] in the 1990s interest in the identification of new and more active catalysts and of the stereochemical characteristics of the reaction has grown. 

Generally, 1,2-disubstituted ethylene derivatives have only a small tendency for radical homopolymerization. An exception is vinylene carbonate (VCA) which can be easily polymerized by chemical as well as radiation initiation. However, the reaction is strongly affected by traces of impurities formed during the synthesis. Inhibition experiments are discussed with regard to the nature of the inhibiting impurities. The copolymerization behavior of VCA with some halo-substituted olefins was studied with chlorotrifluoroethylene (CTFE), a statistical copolymer with a slight tendency for alternation was obtained. 

Supercritical carbon dioxide represents an inexpensive, environmentally benign alternative to conventional solvents for chemical synthesis. In this chapter, we delineate the range of reactions for which supercritical CO2 represents a potentially viable replacement solvent based on solubility considerations and describe the reactors and associated equipment used to explore catalytic and other synthetic reactions in this medium. Three examples of homogeneous catalytic reactions in supercritical CC are presented the copolymerization of CO2 with epoxides, ruthenium>mediated phase transfer oxidation of olefins in a supercritical COa/aqueous system, and the catalyic asymmetric hydrogenation of enamides. The first two classes of reactions proceed in supercritical CO2, but no improvement in reactivity over conventional solvents was observed. Hythogenation reactions, however, exhibit enantioselectivities superior to conventional solvents for several substrates. 

An important aspect of the copolymerization reaction is concerned with the structure of the alternating olefin-carbon monoxide copolymers. Depending on the substituent and on the olefin substrate the materials can be isolated with either the expected polyketone structure 1 (Scheme 2) or the isomeric polyspiroketal structure... 

The practically most important copolymer is made from ethene and propene. Titanium- and vanadium-based catalysts have been used to synthesize copolymers that have a prevailingly random, block, or alternating structure. Only with Ziegler or single site catalyst, longer-chain a-olefins can be used as comonomer (e.g., propene, 1-butene, 1-hexene, 1-octene). In contrast to this, by radical high-pressure polymerization it is also possible to incorporate functional monomers (e.g., carbon monoxide, vinyl acetate). The polymerization could be carried out in solution, slurry, or gas phase. It is generally accepted [173] that the best way to compare monomer reactivities in a particular polymerization reaction is by comparison of their reactivity ratios in copolymerization reactions. 

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