The organocatalytic coupling of CO with oxetanes is investigated under solvent-free conditions. The influence of the main reaction parameters (type of organocatalytic system, pressure, and temperature) on the yield, the product formed, and the selectivity of the reaction are discussed. An onium salt combined with a fluorinated alcohol promotes the efficient and selective organocatalytic synthesis of α,ω-hydroxyl oligocarbonates by coupling CO with oxetanes at 130 °C and at a CO pressure as low as 2 MPa. NMR characterizations were correlated with matrix-assisted laser desorption/ionization with time-of-flight mass spectrometer (MALDI-TOF) analyses for elucidating the structure of the oligomers. Online FTIR studies under pressure, NMR titrations, and DFT calculations allowed an in-depth understanding of the reaction mechanism. Finally, CO -based poly(carbonate-co-urethane)s were synthesized by step-growth polymerization of hydroxyl telechelic oligocarbonates with 4,4'-methylene diphenyl diisocyanate (MDI). The organocatalytic system described herein constitutes an innovative sustainable route to the selective preparation of hydroxyl telechelic carbonates of high interest for many applications, notably for the polyurethane business (especially for coatings or foams).
The metal-free coupling of a propargylic alcohol with CO catalysed by guanidine derivatives was investigated in detail through the combination of online kinetic studies by in situ attenuated-total reflection IR (ATR-IR) spectroscopy and DFT calculations. Bicyclic guanidines, namely 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) and 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene (MTBD) are effective catalysts for the conversion of 2-methyl-3-butyn-2-ol to α-methylene cyclic carbonate and oxoalkyl acyclic carbonate under mild reaction conditions. The lower selectivity of TBD in comparison with MTBD towards the formation of α-methylene cyclic carbonate was elucidated from DFT calculations and is related to the bifunctional activity (base/H-bond donor) of TBD decreasing the Gibbs free energy of the reaction path for the formation of the acyclic carbonate.
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