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.

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The addition of water as a chain transfer reagent during the copolymerization reaction of epoxides and carbon dioxide has been shown as a promising method for producing CO 2 -based polycarbonate polyols. These polyols can serve as drop-in replacements for petroleum derived polyols for polyurethane production or designer block copolymers. Ironically, during the history of CO 2 /epoxide coupling development, water was generally considered primarily as an aversion reagent. That is, in its presence, low catalytic activity and high polydispersity was normally observed. Recently, we reported a water-mediated tandem metal-coordination CO 2 /epoxide copolymerization and organobase catalyzed ring-opening polymerization (ROP) approach for the one-pot synthesis of an ABA CO 2 -based triblock copolymers. As in previous studies, water was deemed as the chain transfer reagent in this tandem strategy for producing CO 2 -based polyols. Herein is presented a mechanistic study aimed at determining the intimate role water plays during the metal-catalyzed CO 2 /epoxide copolymerization process. In this regard, it was observed that under the commonly employed (salen)Co(trifluoroacetate)/onium salt binary catalyst system, water was not the true chain-transfer reagent, but instead reacted initially with the epoxides to afford the corresponding diols which serves as the chain-transfer reagent. The further studies in resultant afforded α,ω-dihydroxyl endcapped polycarbonates were utilized in direct chain extension via ROP of the water-soluble cyclic phosphate monomer, 2methoxy-2-oxo-1,3,2-dioxaphospholene employing an organocatalyst. These triblock copolymers displayed narrow PDI and were found to provide nanostructure materials which should be of use in biomedical applications.

The physical properties and structures of a series of six complexes of the type (NiN(2)S(2))W(CO)(4) have been used to establish electronic and steric parameters for square planar NiN(2)S(2) complexes as bidentate, S-donor ligands. According to the nu(CO) stretching frequencies and associated computed Cotton-Kraihanzel force constants of the tungsten carbonyl adducts, there is little difference in donor abilities of the five neutral NiN(2)S(2) metallodithiolate ligands in the series. The dianionic Ni(ema)(2)(-) (ema = N,N'-ethylenebis(2-mercaptoacetamide)) complex transfers more electron density onto the W(CO)(4) moiety. A ranking of donor abilities and a comparison with classical bidentate ligands is as follows: Ni(ema)(=) > {[NiN(2)S(2)](0)} > bipy approximately phen > Ph(2)PCH(2)CH(2)PPh(2) > Ph(2)PCH(2)PPh(2). Electrochemical data from cyclic voltammetry find that the reduction event in the (NiN(2)S(2))W(CO)(4) derivatives is shifted to more positive potentials by ca. 0.5 V compared to the ca. -2 V Ni(II/I) redox event in the free NiN(2)S(2) ligand, consistent with the electron drain from the nickel-dithiolate ligands by the W(CO)(4) acceptor. Differences in Ni(II/I) DeltaE(1/2) values appear to have a ligand dependence which is related to a structural feature of the hinge angle imposed by the (mu-SR)(2) bridges. Thus the angle formed by the intersection of NiN(2)S(2)/WS(2)C(2) planes has been established by X-ray diffraction analyses as a unique orientational feature of the nickel-dithiolate ligands in contrast to classical diphosphine or diimine ligands and ranges in value from 136 to 107 degrees . Variable-temperature (13)C NMR studies show that the spatial orientations of the ligands remained fixed with respect to the W(CO)(4) moiety to temperatures of 100 degrees C.

The observation of nearly identical infrared spectra in the diatomic (2000 cm -1 ) region of oxidized forms of [NiFe]hydrogenases, as isolated from