CO-olefin copolymerization

A key impetus in the study of these materials was the pursuit of catalytic CO/olefin copolymerization, reactivity to which 431-438 and 447 and their parent alkyls are entirely inert. Though 448 has been found to react with norbomadiene, affording the insertion product Tp PdC7H8C (O)p-Tol) (449), it does so slowly (>1 day). However, when the parent p-Tolyl complex 440 is simultaneously exposed to both CO and norbor-nadiene, catalytic copolymerization ensues, affording the polyketone within hours (Section IV.A).140 141... 

Table 1. A comparison of Pd-catalyzed CO/olefin copolymerization and early-transition-metal-catalyzed olefin polymerization.

To enhance understanding of the CO-olefin copolymerization reaction catalyzed by nickel organometallic complexes (for the similar copolymerization reaction catalyzed by palladium compounds, see below), consider the carbon monoxide insertion reaction with nickel(II) compounds containing the bidentate P, O donor B ... 

Carbon monoxide insertions into palladium-alkyl or palladium-aryl bonds were extensively studied in connection with the palladium-catalyzed CO-olefin copolymerization process . 

Figure 2 DPPP and its derivatives and bipyridine-type ligands employed in CO/olefin copolymerization.

Water-soluble l,3-bis(di(hydroxyalkyl)phosphino)propane derivatives were thoroughly studied as components of Pd-catalysts for CO/ethene (or other a-olefins) copolymerization and for the terpolymerization of CO and ethene with various a-olefins in aqueous solution (Scheme 7.17) [59], The ligands with long hydroxyalkyl chains consistently gave catalysts with higher activity than sulfonated DPPP and this was even more expressed in copolymerization of CO with a-olefins other than ethene (e.g. propene or 1-hexene). Addition of anionic surfactants, such as dodecyl sulfate (potassium salt) resulted in about doubling the productivity of the CO/ethene copolymerization in a water/methanol (30/2) solvent (1.7 kg vs. 0.9 kg copolymer (g Pd)" h" under conditions of [59]) probably due to the concentration of the cationic Pd-catalyst at the interphase region or around the micelles which solubilize the reactants and products. Unfortunately under such conditions stable emulsions are formed which prevent the re-use... 

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 ). 

As well as certain monomer syntheses, defined polymers can be made through homogeneous catalysis, e. g., olefin metathesis (CdF Norsorex , Hills Vestenamer , Hercules DCP ), special ring-opening metathesis (cf. Section 2.3.3), CO/C2H4 copolymerization (cf. Section 2.3.4), and other reactions (cf. Section 3.3.10.1). 

As previously mentioned, the properties of olefm-CO copolymers depend strongly on the nature of the olefin employed. The glass transition temperature of 1-olefin-CO copolymers decreases from room temperature to nearly -60 °C upon increasing the chain length of the 1-olefin from propylene to 1-dodecene [33]. By contrast to polar ethylene-CO copolymers, copolymers with higher l-olefins display a hydrophobic character. For 1-olefin copolymerization, catalysts with entirely alkyl-substituted diphosphine hgands R2P-(CH2) -PR2 (R=alkyl, by comparison to R=Ph in dppp) such as 3 are particularly well-suited [48]. Efhylene-l-olefin-CO terpolymers and 1-olefin-CO copolymers can be prepared in aqueous polymerizations [43, 47, 48]. In the aforementioned copolymerization reactions, the polyketone was reported to precipitate during the reaction as a sohd [45, 47, 48, 50]. However, in the presence of an emulsifier such as sodium dodecyl sulfate (SDS) and under otherwise suitable conditions, stable polymer latexes can be obtained. 

SCHEME 22.1 Initiation, propagation, and chain transfer for olefin/CO alternating copolymerization initiated by (a) a palladium dication in the presence of methanol, or (b) an alkylpalladium cation in an aprotic solvent. (L2 is a cis-chelating bidentate ligand L"L and S represents solvent(s).)... 

Up to now, palladium complexes do not play a significant role in the hydroformylation of olefins [1]. However, because of their widespread use in the related hydrocarboxylation, hydroesterification, and olefin copolymerization with CO [2], occasionally their utility for hydroformylation was elucidated [3]. Moreover, palladium catalysts have been used for the hydroformylation of aryl and enol triflates to produce the corresponding unsaturated aldehydes [4]. 

Scheme 1 Initiation, propagation, and chain transfer of the olefin/CO alternating copolymerization initiated by a palladium dication or an alkylpalladium cation.

Elemental analyses and the spectroscopic data are consistent with the styrene-co-B-vinylborazine formulations. By adjusting the monomer feed ratios and the initiator concentrations, copolymers ranging in composition from 10 to 90% styrene and molecular weights from -1,000 to >1,000,000 can be producted. The use of these AIBN initiated olefin copolymerization reactions are now being explored as routes to a wide variety of borazine-containing hybrid organic polymers. 

Kunitake, Yamaguchi and Aso149 studied the copolymerization of 2-furaldehyde with olefins and vinyl ethers using BF3 Et20 in methylene chloride or toluene at —78 °C. No copolymers were obtained with olefins, but p-tolyl vinyl ether or 2,3-dihydropyran gave polyethers. With the former co-monomer the values of the reactivity ratios were rx = 0.15 0.15 and r2 = 0.25 0.05 (Mj = 2-furaldehyde). 

Water-soluble dicationic palladium(II) complexes [(R.2P(CH2)3PR.2)Pd-(NCMe)2][BF4]2 proved to be highly active in the carbon monox-ide/ethene copolymerization under biphasic conditions (water-toluene). In the presence of an emulsifier and methanol as activator, the catalytic activity increased by a factor of about three. Also higher olefins could be successfully incorporated into the copolymerization with CO and the terpolymerization with ethene and CO.184... 

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 diimine palladium compounds are less active than their nickel analogs, producing highly branched (e.g., 100 branches per 1,000 carbons) PE. However, they may be used for the copolymerization of Q-olefins with polar co-monomers such as methyl acrylate.318,319 Cationic derivatives, such as (121), have been reported to initiate the living polymerization of ethylene at 5°C and 100-400 psi.320 The catalyst is long-lived under these conditions and monodisperse PE (Mw/Mn= 1.05-1.08) may be prepared with a linear increase in Mn vs. time. 

In contrast to the free-radical polymerizations, there have been relatively few studies on transition metal catalysed polymerization reactions in water. This is largely due to the fact that the early transition metal catalysts used commercially for the polymerization of olefins tend to be very water-sensitive. However, with the development of late transition metal catalysts for olefin polymerizations, water is beginning to be exploited as a medium for this type of polymerization reaction. For example, cationic Pd(II)-bisphosphine complexes have been found to be active catalysts for olefin-CO copolymerization [21]. Solubility of the catalyst in water is achieved by using a sulfonated phosphine ligand (Figure 10.5) as described in Chapter 5. 

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