Of polyketones

The selective formation of the 3-monosemicarbazones of polyketonic steroids can be achieved only in the presence of 21-acetoxy-20-ketones by the use of nonbuffered conditions. Partial hydrolysis of 3,20-bissemicar-bazones can be achieved with acetic anhydride in pyridine "" to yield the 3-semicarbazone. Kinetic studies on the rates of formation of Girard hydra-zones showed that the A" -3-ketone is less reactive than the saturated 3- and 6-ketones, as reactive as the 7- and 17-ketones and more reactive than the 20- and 12-ketones. ... 

Recently developed catalyst systems make it possible to construct carbon (.v/>2 )-catbon (sp3) bonds and carbon-nitrogen bonds under mild conditions (Scheme 9.14).19,20 These new developments have also been incorporated into step-growth polymerization. Kanbara et al. reported the synthesis of polyanilines and related polymers in 1996 (Scheme 9.15).21 Wang and Wu reported the synthesis of polyketones in 1999 (Scheme 9.16).22... 

The carbonylation of ethene has a wider interest as it can lead to the production not only of polyketones, but also to many other products ranging from low molecular weight cooligoesters, down to methyl propanoate (MP) and also cooligodiesters, cooligodiketones down to diethyl ketone (DEK). The insertion of the monomers into MeOH is schematized by Eq. 1, n ranging from 1 to even more that 10000 ... 

In this chapter we will discuss some aspects of the carbonylation catalysis with the use of palladium catalysts. We will focus on the formation of polyketones consisting of alternating molecules of alkenes and carbon monoxide on the one hand, and esters that may form under the same conditions with the use of similar catalysts from alkenes, CO, and alcohols, on the other hand. As the potential production of polyketone and methyl propanoate obtained from ethene/CO have received a lot of industrial attention we will concentrate on these two products (for a recent monograph on this chemistry see reference [1]). The elementary reactions involved are the same formation of an initiating species, insertion reactions of CO and ethene, and a termination reaction. Multiple alternating (1 1) insertions will lead to polymers or oligomers whereas a stoichiometry of 1 1 1 for CO, ethene, and alcohol leads to an ester. 

It was Ayusman Sen [8] who discovered in 1982 that the use of weakly coordinating anions and phosphines as the ligands together with palladium yielded much more stable and active catalysts for the formation of polyketone from CO and ethene in alcoholic solvents. Cationic palladium-(triphenylphosphine)2(BF4)2 gave a mixture of oligomers having methoxy ester... 

FIGURE 6.16 Formation of polyketones in the OH reaction with p-xylene (adapted from Wiesen et al 1995). 

As shown in equation 21, the methylenation of polyketone is performed with bis(iod-ozincio)methane (3) and /S-TiCl339. With these substrates, the Wittig reagent and the... 

Chatani, Y., T. Tazikawa, S. Mcrahashi, Y. Sakata, and Y. Nishimura Crystal structure of polyketone (1 1 ethylene/carbon monoxide) copolymer. J. Polymer Sci. 55, 811 (1961). 

The application of polyketone-derived anions to the synthesis of oxygen heterocycles has much to offer a comprehensive review of this area has been published (77T2159). 

Higher aliphatic 1-alkenes exhibit a slightly lower reactivity as compared with propene, but the head-to-tail as well as isotactic selectivity is as high as that observed for propene [132,133], The copolymers arising from higher 1-alkenes tend to possess the poly spiroketal form more extensively as compared with the propene/CO copolymer. For example, poly(l -hexene-a/r-CO) exists as a mixture of polyketone and polyspiroketal, even in a CDC13 solution based on 13C NMR analysis [133]. 

Recent developments in the use of organic costabilisers for stabilisation of PVC are reviewed, with particular attention to a new class of polyketones (pyrrolidine-2,4-diones) recently patented by Akcros Chemicals. The... 

While certain intereshng aspects have been recently discovered, the potential of BVMO-mediated biooxygenation of multifunctional substrates and, in particular, of polyketone compounds, is yet to be fully investigated. Further studies in this area certainly contain the prospect of high impact contributions for the further improvement and increase in efficiency for future applications in single-operation multistep synthesis. 

ZIGZAG BORON CARBON CHAINS IN YBC INORGANIC ANALOGS OF POLYKETONE... 

To the best of our knowledge, only two papers on the oxidation of polyketonates have been published. Lintvedt and coworkers have observed that the binuclear complex Co2(dbba)2py4 (136) reacts with O2 in pyridine/benzene affording the binuclear derivative 137, derived from the oxidation of the 4-methyne carbon of both ligands to carbonyl groups (equation 87). At variance with the S-diketonates, which are decomposed upon oxidation at the methyne carbon atom (Section 1V.A.2), the CH2 C=0 oxidation at C4 in the tetraketonato complex does not destroy the dianion character of the ligand, preserving the complex coordination. 

In addition to the synthesis problems mentioned above, unsurmountable processing problems were eneountered for the resulting polymers. Extensive erosslinking under melt proeessing eonditions led to a lack of significant thermoplastic properties of the resulting materials, and this also presented a major developmental hurdle. At the end of the 1970s, it was therefore concluded that the polymer baekbone of polyketone was inherently unstable and that polyketones eould not be efficiently produced. Both conclusions proved to be invalid. 

In the early 1980s, workers at Shell could demonstrate melt processability of polyketone produeed by palladium cyanide catalysts, after extensive extraction of catalyst residues from the polymers and blending these with other polymers such as styrene/acrylonitrile copolymer. From these studies, it was suggested that thermoplastic properties were possible in principle, and that the polyketone backbone was not inherently unstable in the melt as previously concluded. However, catalyst extraction did not offer a viable production option from a technical and economic viewpoint. 

This discovery of the combined importance for high catalyst activity of biden-tate ligands and weakly coordinating anions around a cationic palladium(II) center has, for the first time, given access to efficient synthesis of polyketones. These new catalysts opened the way to economically attractive production and, equally important, provided much more stable polymers with catalyst residues now measured in parts per million rather than percentages. Polyketone thermoplastics have been developed to be easily melt-processable, and could therefore be shown to exhibit a unique set of desirable engineering thermoplastic properties [2]. 

Figure 1. Influence of chain length of ligand Ph2P(CH2)nPPh2 on polymerization rate and molecular weight of polyketone.

Although the basic principles of polyketone formation are now reasonably well understood, further studies, both of polymerization characteristics and of the elementary steps underlying polyketone catalysis, will be needed to exploit fully the potential of these selective polymerizations. 

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