Alkoxide-Initiated Regioselective Coupling of Carbon Disulfide and Terminal Epoxides for the Synthesis of Strongly Alternating Copolymers

Abstract

The synthesis of highly regioregular and alternating polythiocarbonates from carbon disulfide and terminal epoxides has been achieved. The copolymerizations were performed under ambient and solvent-free conditions in the presence of LiO t Bu (0.125−0.5 mol %) as initiator. At higher loadings the reaction pathway switched in favor to the catalytic formation of cyclic dithiocarbonates. Under optimized reaction conditions polymers with molecular weights up to 109 kg mol −1 were isolated. The NMR spectroscopic analysis of the polythiocarbonates revealed that 94% of backbone structure is formed by strongly alternating head-to-head arrangement of epoxypropane and 1,2-epoxybutane monomers, respectively, at a thiocarbonate group −CHR−OC(S)O−CHR− and tail-to-tail arrangement at a trithiocarbonate group −CH 2 −SC(S)S−CH 2 −. Atactic polymers were obtained using racemic mixtures of the epoxides, but an isotactic polymer was obtained when chiral (R)-epoxypropane was converted. A mechanism is proposed which rationalizes the regio-and stereochemistry observed for the alkoxide-initiated copolymerization of CS 2 and terminal epoxides.

Atom economical synthesis of di- and trithiocarbonates by the lithium tert-butoxide catalyzed addition of carbon disulfide to epoxides and thiiranes

“…4A). 58,59 Thus, the rising broad resonances around 82.1 ppm can neither clearly be ascribed to adduct 9 nor to oligomer 8 (Fig. 4B).…”

“…1 and ESI †). 59 The highest isolated yield of 86% was obtained in the presence of 5 mol% LiO t Bu. However, LiO t Bu lithium led to full conversion of the substrate and a good selectivity of 89% towards 4-ethyl-1,3-oxathiolane-2-one (2a) was achieved.…”

“…[48][49][50][51][52] Even though great advances in respect of the chemo-and regioselectivity have been made, the methods reported so far often require long reaction times (up to 24 h), elevated temperatures (up to 100°C), high catalyst loadings (up to 10 mol%) and the use of solvents and/or additives. 58,59 Herein we give a full account of the use of readily available alkoxides as catalysts for the cycloaddition of CS 2 to terminal and internal epoxides 1 as well as thiiranes 3. 26,32,[53][54][55][56][57] Most recently we turned our attention to the conversion of carbon disulfide in this reaction.…”

An Investigation on the Production of Random Copolymer with Monothiocarbonate and Trithiocarbonate Units over Cyclic Thiocarbonate via Metal‐free Catalysis

“…As a result, five different polymer linkages and two cyclic products were revealed by 1 H and 13 C NMR spectroscopy, and a plausible mechanism on a tetrahedral intermediate was presented based on the result of in situ infrared spectroscopic monitoring of the polymerization process. After that, Werner and his coworkers used metal alkoxide as a catalyst to mediate the reaction of CS 2 with different epoxides, and similar mechanism was proposed for O‐S ER process. In particular, catalyst loading was found to have a decisive effect on the product composition for this catalyst system.…”

“…Varying the tendency of O‐S ER might be used as an effective method to tune the sulfur content in the polymer chain. Meanwhile introduction of sulfur atom in the polymer chain is beneficial to increasing refractive index (RI) of the resulted copolymer . The thusly formed high RI polymer is an important class of materials that have been widely developed in recent years for optical components due to their lightweight, high impact resistance, low cost and easy processing .…”