Oxetane/carbon dioxide

Oxetane (oxacyclobutane) has been copolymerised successfully with carbon dioxide to give poly(trimethylene ether-carbonate) in the presence of the triethy-laluminium water acetylacetone (2 1 1) catalyst (Table 9.4) [scheme (35)]. The carbon dioxide content in the copolymer produced was ca 20 mol.-%. Attempts to carry out oxetane/carbon dioxide copolymerisation with the diethylzinc water (1 1) catalyst failed to give any copolymer [245],... 

The fluorovinyllithium reagents are thermally unstable (vu/e supra) and are reacted with electro-philes at low temperatures. These reagents undergo usual reactions with a variety of electrophiles including ketones, esters, alkanoyl chlorides, epoxides (e.g.. formation of 6 ), oxetanes, carbon dioxide, sulfur dioxide, tin and silicon halides, and trifluoromethancsulfonates. The reaction of 2,2-difluoro-1 -(tosyloxy)vinyllithium (5) with trialkylboranes followed by a second electrophile is an attractive route to functionalized 1.1-difluoroalkenes. e.g. 7. ... 

Abstract This chapter focuses on well-defined metal complexes that serve as homogeneous catalysts for the production of polycarbonates from epoxides or oxetanes and carbon dioxide. Emphasis is placed on the use of salen metal complexes, mainly derived from the transition metals chromium and cobalt, in the presence of onium salts as catalysts for the coupling of carbon dioxide with these cyclic ethers. Special considerations are given to the mechanistic pathways involved in these processes for the production of these important polymeric materials. 

Keywords Carbon dioxide Copolymerization Oxetanes Polycarbonates Schiff-base ligands... 

Carbon dioxide is a widely available, inexpensive, and renewable resource. Hence, its utilization as a source of chemical carbon or as a solvent in chemical synthesis can lead to less of an impact on the environment than alternative processes. The preparation of aliphatic polycarbonates via the coupling of epoxides or oxetanes with CO2 illustrates processes where carbon dioxide can serve in both capacities, i.e., as a monomer and as a solvent. The reactions represented in (1) and (2) are two of the most well-studied instances of using carbon dioxide in chemical synthesis of polymeric materials, and represent environmentally benign routes to these biodegradable polymers. We and others have comprehensively reviewed this important area of chemistry fairly recently. Nevertheless, because of the intense interest and activity in this discipline, regular updates are warranted. 

Scheme 8 Mechanistic pathways for the copolymerization of oxetane and carbon dioxide...

MS fragmentation of a series of 13 4-aryl-3,3-dichloro-2-oxetanes (18) has been reported to give the dichloroketene cation as the base peak in every case, except for the 4-(m-methoxyphenyl) compound. There the base peak was for the m-methoxybenzaldehyde cation. The results were in marked contrast to the cleavage seen on thermolysis, which gave carbon dioxide and the corresponding/3,j8-dichlorostyrene (78JHC1165). 

Phenyl- and vinyl-substituted oxetanes are more labile and tend to decompose at 250-300 °C. 2-Oxetanones are very sensitive to thermolysis, often decomposing with loss of carbon dioxide at temperatures of about 100 °C. Oxetenes are thermally unstable at room temperature. 

Oxetanes can be copolymerized very successfully with a wide range of other monomers and even carbon dioxide, to give plastic compositions with a wide variety of properties. Naturally, this area has been the subject of a great deal of research, and many patents have appeared which are beyond the scope of this survey. 

Physical Methods for the Characterization of Copolymers Produced from Epoxides or Oxetane and Carbon Dioxide... 

However, organotin-based catalyst systems such as BU2S11I2 or BU3S11I—PBU3, PPI13 or NEt3 have been found to promote the alternating copolymerisation of oxetane and carbon dioxide to yield poly(trimethylene carbonate) ... 

Cyclic carbonates of 1,3-propanediols yield thietanes when treated with thiocyanate ion and heated until carbon dioxide is evolved. Yields vary from 3 to 63%, the yield being greater for 3,3-disubstituted thietanes, as illustrated in the synthesis of the spirothietane, 44. Oxetanes are formed as byproducts in... 

Scheme 4.1 Synthesis of poly(trimethylene carbonate) (PTMC) by reaction of carbon dioxide with oxetane. TMC, trimethylene carbonate.

Baba, A., Meishou, H., Matsuda, H., 1984. Copolymerization of oxetane with carbon dioxide with organotin halide/lewis base systems. Makromolekulare Chemie Rapid Communications 5, 665—668. 

Darensbourg, D., Moncada, A.I., Choi, W., Reiebenspies, J.H., 2008. Mechanistic smdies of the copolymerization reaction of oxetane and carbon dioxide to provide aliphatic polycarbonates catalyzed by (Salen)CrX complexes. Journal of the American Chemical Society 130, 6523-6533. 

Rintjema, J., Guo, W., Martin, E., Escudero-Adan, E.C., Kleij, A.W., 2015. Highly chemo-selective catalytic coupling of substituted oxetanes and carbon dioxide. Chemistry — A European Journal 21, 10754—10762. 

The reaction of oxetane with carbon dioxide in the presence of tetraphenylstibonium iodide affords the six-membered ring [4-1-1] cycloadduct 87 ... 

Schiff base catalyst was also active in TMC polymerization. Moreover, chromium(III) salen derivatives in the presence of anionic initiators have been shown to be very effective catalytic systems for the alternating copolymerization of oxetane and carbon dioxide to provide the corresponding PC with a minimal amount of ether linkages. The best results were achieved for the salen ligand with tert-butyl groups in the 3,5-positions of the phenolate rings and a cyclohexylene backbone for the diimine along with an azide ion initiator (Scheme 57). 

The determined free energies of activation for these two reactions, namely 101.9 kj mol" for ROP of TMC and 107.6 kj mol" for copolymerization of oxetane and carbon dioxide, support this conclusion. 

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