Poly(monothiocarbonate)s from the Alternating and Regioselective Copolymerization of Carbonyl Sulfide with Epoxides

Abstract

Carbonyl sulfide (COS) is an air pollutant that causes acid rain, ozonosphere damage, and carbon dioxide (CO) generation. It is a heterocumulene and structural analogue of CO. Relevant to organic synthesis, it is a source of C═O or C═S groups and thus an ideal one-carbon (C1) building block for synthesizing sulfur-containing polymers through the similar route of CO copolymerization. In contrast, traditional synthesis of sulfur-containing polymers often involves the condensation of thiols with phosgene and ring-opening polymerization of cyclic thiocarbonates that are generally derived from thiols and phosgene; thus, COS/epoxide copolymerization is a "greener" route to supplement or supplant current processes for the production of sulfur-containing polymers. This Accounts highlights our efforts on the discovery of the selective formation of poly(monothiocarbonate)s from COS with epoxides via heterogeneous zinc-cobalt double metal cyanide complex (Zn-Co(III) DMCC) and homogeneous (salen)CrX complexes. The catalytic activity and selectivity of Zn-Co(III) DMCC for COS/epoxide copolymerization are similar to those for CO/epoxide copolymerization. (salen)CrX complexes accompanied by onium salts exhibited high activity and selectivity for COS/epoxide copolymerization under mild conditions, affording copolymers with >99% monothiocarbonate units and high tail-to-head content up to 99%. By way of contrast, these catalysts often show moderate or low activity for CO/epoxide copolymerization. Of note, a specialty of COS/epoxide copolymerization is the occurrence of an oxygen-sulfur exchange reaction (O/S ER), which may produce carbonate and dithiocarbonate units. O/S ER, which are induced by the metal-OH bond regenerated by chain transfer reactions, can be kinetically inhibited by changing the reaction conditions. We provide a thorough mechanistic understanding of the electronic/steric effect of the catalysts on the regioselectivity of COS copolymerization. The regioselectivity of the copolymerization originates from the solely nucleophilic attack of the sulfur anion to methylene of the epoxide, and thus, the chiral configuration of the monosubstituted epoxides is retained. COS-based copolymers are highly transparent sulfur-containing polymers with excellent optical properties, such as high refractive index and Abbe number. Thanks to their good solubility and many available epoxides, COS/epoxide copolymers can potentially be a new applicable optical material. Very recently, crystalline COS-based polymers with or without chiral carbons have been synthesized, which may further expand the scope of application of these new materials.

Chromium(III) and Chromium(II) Phenolate Complexes with Bulky Alkylcyclopentadienyl Ligands

“…In analogy to reactions of the easily available molybdenum or tungsten half sandwich complexes [CpM(CO) 3 …”

Anionic Copolymerization of Carbonyl Sulfide with Epoxides via Alkali Metal Alkoxides

“…Unfortunately, the related works are still rare. [16,17] It is very promising to synthesize poly(monothiocarbonate)s [16] by the copolymerization of COS with epoxides. These sulfur-containing polymers have unique properties, such as high transparency, high refractive index, excellent chemical resistance and heavy-metal recognition ability.…”

“…[18][19] Crystalline poly(monothiocarbonate)s with high melting temperatures and excellent mechanical properties can also be synthesized by COS and oxetane or ethylene oxide. [20][21] In contrast to the previously reported condensation reaction involved with toxic phosgene and dithiol, and ring-opening polymerization (ROP) of the cyclic thiocarbonates that required multiple synthetic and separation steps, [16] such copolymerization is an atom-economic route to utilize COS.…”

“…Unfortunately, oxygen/sulfur exchange reaction (OS/ER) [31][32][33] produced trithiocarbonate, dithiocarbonate and carbonate units randomly distributed in the polymer chain. Since COS is an asymmetric CO 2 (CS 2 ) analogue and has higher reactivity than CO 2 and poorer ability of O/S ER than CS 2 , [16,[31][32][33] we envisioned that COS could copolymerize with epoxides in an anionic copolymerization process.…”

Synthesis of Chiral Sulfur‐Containing Polymers: Asymmetric Copolymerization of meso‐Epoxides and Carbonyl Sulfide

“…Thep roduced poly(trithiocarbonate) possessed ah igh refractive index. [11] Some efficient catalyst systems possessing excellent activities and high regioselectivities were developed to produce poly(monothiocarbonate)s with an alternating structure and no oxygensulfur exchange. [10] Recently,c arbonyl sulfide (COS) as as ulfur source for building sulfur-containing polymers,b yc opolymerization with epoxides,has received much attention.…”