Abstract
We report a rational investigation of the selective synthesis of poly(cyclohexene carbonate) from CO2 and cyclohexene oxide by using commercially available Lewis acids with nontoxic metal centers. After a preliminary screening, we focused on the use of zinc salts, and the effect of the pressure, the temperature, the catalyst loading, and the presence of cocatalyst or a solvent on the reaction yields, selectivity, and molar masses was evaluated for selected catalytic platforms. Thus, we found that ZnTosylate in catalytic amounts under solvent- and cocatalyst-free conditions enables the selective synthesis of poly(cyclohexene carbonate) with a molecular weight of about 62.1 kg/mol with about 70% yields at 343 K and 4 MPa. To the best of our knowledge, this is a rare example of high molar mass polycyclohexene carbonates that are moreover obtained under solvent- and cocatalyst-free conditions. The high selectivity of ZnTos towards the formation of poly(cyclohexene carbonate) was interpreted, thanks to in situ FTIR spectroscopy and DFT calculations, as resulting from its ability to coactivate CO2.
Highlights
Catalytic Studies Performed with Metal Triflates Complexes Series of metal triflates complexes catalysts were screened in combination with nucleophilic cocatalysts for the solvent-free coupling of CO2 with cyclohexene oxide which can lead to the formation of cyclic carbonate, polycarbonate, and polyether products (Scheme 1)
It appears clearly that these strong Lewis acid species that activate the epoxide towards ring opening allow mainly the consecutive insertion of two epoxides leading to the formation of polyethers
In order to favor the alternating copolymerization of CO2 and cyclohexene oxide and improve the selectivity of the Sc, Y, and Zn complexes towards the formation of poly(cyclohexene carbonate) (PCHC), we investigated various cocatalysts of different types with different relative catalyst/cocatalyst ratios
Summary
1. Introduction The valorization of carbon dioxide (CO2) as a renewable C1 feedstock to produce fine chemicals or polyTmheervsaisloorfizgartoiowninogf icnatrebroenstdinioaxciaddee(mCiOc2l)aabsoraarteonrieews aanbdleiCnd1ufesetrdiesstoicnkthtoe pcorondteuxcteoffinsuescthaienmabiclaels choermpisotlryym[1e–rs11i]s. Ionf tghrisowcoinntgexitn,ttehreesctouinplaincgadoefmCiOc 2lawbiotrhateoproiexsidaensdthaintdleuasdtrsietso tihnetfhoermcoatnitoenxtofof cysculisctacianrabbolneactehseomripstorlyyc[a1r–b1o1n].atIens tihsias hciognhtleyxat,tttrhaecticvoeu1p0li0n%g aotfomCO-e2cowniotmh iecproexaicdtieosn.thBaotthlepadrosdtuocttshe arfeorvmalautaiobnleocfhceymcliiccaclasrtbhoant astheosuolrdpboelyscealercbtoivnealtyespirsoadhuicgehdlyinaottrrdaectrivtoe m10i0n%imaitzoemth-eecsoenpoamraictiorenaactniodn. ATtehse[s1e2l–e1c5ti]v, iptyoloyfcathrbisonreaatecsti[o1n,2i,s16d–e1p8e],nodrepntoloynetthheersniastustrreonogf ltyhe reslautbesdtrtaotethaencdhotihcee offoarnmaaptipornoporfiaeteithcaetralcyysctl(iScchcaemrbeon1a).tes [12,13,14,15], polycarbonates [1,2,16,17,18], or polyethers is strongly related to the choice of an appropriate catalyst (Scheme 1). The CO2/cyclohexene oxide (CHO) coupling leading to various possible products: cyclic cySclcohheemxeen1e.cTahrbeoCnOat2e/c(yCcHloCh)e,xpeonley(ocyxicdloeh(eCxHenOe)cacorbuopnlainteg) l(ePaCdHinCg),toanvdarpiooluys(cpyoclsoshibelxeepneroedthuecrt)s:(PcyEc).lic cyclohexene carbonate (CHC), poly(cyclohexene carbonate) (PCHC), and poly(cyclohexene ether) (PE).
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