Transforming how plastics are made, unmade, and remade through innovative research and diverse partnerships that together foster environmental stewardship is critically important to a sustainable future. Designing, preparing, and implementing polymers derived from renewable resources for a wide range of advanced applications that promote future economic development, energy efficiency, and environmental sustainability are all central to these efforts. In this Chemical Reviews contribution, we take a comprehensive, integrated approach to summarize important and impactful contributions to this broad research arena. The Review highlights signature accomplishments across a broad research portfolio and is organized into four wide-ranging research themes that address the topic in a comprehensive manner: Feedstocks, Polymerization Processes and Techniques, Intended Use, and End of Use. We emphasize those successes that benefitted from collaborative engagements across disciplinary lines.

Polyesters constitute around 10% of the global plastic market with aromatic polyesters, such as poly(ethylene terephthalate) (PET), being the most prevalent because of their attractive properties. As for most commercial plastics, polyesters are primarily derived from fossil resources and are not readily degradable, which raises a number of sustainability concerns. Designing polymers with competitive properties from sustainable feedstocks that rapidly degrade under mild conditions is an attractive strategy for addressing the current plastic waste problem. Here, the detailed synthesis and characterization of degradable, high molar mass aromatic polyesters derived from salicylic acid, poly(salicylic glycolide) (PSG), and poly(salicylic methyl glycolide) (PSMG) are described. The synthesis of polymers was investigated through mechanistic experiments and complementary computational studies. The glass transition temperature (T g ≈ 85 °C) and Young's modulus (E ≈ 2.3 GPa) of these polyesters are comparable to those of PET. In contrast to the poor hydrolytic degradability of PET, both PSG and PSMG are readily degradable in neutral aqueous solutions (e.g., complete degradation in seawater at 50 °C in 60 days). These aromatic polyesters derived from salicylic acid have potential as future high-performance, sustainable, and degradable plastics.

N-heterocyclic carbenes (NHCs) belong to the popular family of organocatalysts used in a wide range of reactions, including that for the synthesis of complex natural products and biologically active compounds....

The control of the tacticity of synthetic polymers enables the realization of emergent physical properties from readily available starting materials. While stereodefined polymers derived from nonpolar vinyl monomers can be efficiently prepared using early transition metal catalysts, general methods for the stereoselective polymerization of polar vinyl monomers remain underdeveloped. We recently demonstrated asymmetric ion pairing catalysis as an effective approach to achieve stereoselective cationic polymerization of vinyl ethers. Herein, we provide a deeper understanding of stereoselective ion-pairing polymerization through comprehensive experimental and computational studies. These findings demonstrate the importance of ligand deceleration effects for the identification of reaction conditions that enhance stereoselectivity, which was supported by computational studies that identified the solution-state catalyst structure. An evaluation of monomer substrates with systematic variations in steric parameters and functional group identities established key structure−reactivity relationships for stereoselective homo-and copolymerization. Expansion of the monomer scope to include enantioenriched vinyl ethers enabled the preparation of an isotactic poly(vinyl ether) with the highest stereoselectivity (95.1% ± 0.1 meso diads) reported to date, which occurred when monomer and catalyst stereochemistry were fully matched under a triple diastereocontrol model. The more complete understanding of stereoselective cationic polymerization reported herein offers a foundation for the design of improved catalytic systems and for the translation of isotactic poly(vinyl ether)s to applied areas.

We report the facile synthesis and characterization of 1,6-α linked functional stereoregular polysaccharides from biomass-derived levoglucosan via cationic ring-opening polymerization (cROP). Levoglucosan is a bicyclic acetal with rich hydroxyl functionality,...

The mechanism and stereoselectivity in a chiral N-heterocyclic carbene-catalyzed desymmetrization of a 1,3-diketone is established by using density functional theory computations. The Breslow intermediate formation is identified to involve Hunig's base-assisted proton transfer. The relative energies of stereoselectivity-determining intramolecular aldol cyclization transition states reveal that in the most preferred mode the re-face of enolate adds to the si-face of carbonyl leading to a tricyclic lactone with a configuration (2aS,4aS,8'S) in excellent agreement with previous experimental reports.

Contemporary literature offers a number of interesting examples for asymmetric multicatalytic reactions using chiral N-heterocyclic carbenes (NHCs) in conjunction with other catalysts. One of the very recent examples demonstrated a convenient strategy toward realizing chiral benzofuranones from salicylaldehyde and dimethyl acetylenedicarboxylate (DMAD). In this article, we report the mechanism and insights on the origin of asymmetric induction as obtained through a comprehensive density functional theory (M06-2X and mPW1K) investigation. Different likely catalyst−substrate combinations as well as the timing/sequence of activation of different substrates are carefully examined so as to identify the most preferred pathway. In the lowest energy path, the activation of DMAD by quinuclidine occurs first; the resulting zwitterionic intermediate then undergoes a Michael addition with a salicylate ion to yield a salicylate−DMAD adduct, which, in turn, is intercepted by the chiral NHC. In the next crucial step, an enantioselective C−C bond formation via an intramolecular Stetter reaction furnishes the benzofuranone framework bearing a chiral carbon atom. Two transition state models, with and without an explicitly bound catechol (an additive employed in the reaction that resulted in enhanced enantioselectivity), are considered. A distinct energetic advantage, of the order of 3.4 kcal/mol, for the addition of the re face of the Breslow intermediate (derived from the chiral NHC and the salicylate−DMAD adduct) to the re face of the dimethyl maleate moiety is noticed in the stereocontrolling C−C bond formation step. The Gibbs free energy difference between the diastereomeric transition states for (re,re) and (re,si) modes of addition is traced to the differential nonbonding interactions (O−H•••π, lone pair (lp)•••π, and C−H••• O). The predicted enantioselectivity is in good agreement with the experimental observations.

A new class of PNP pincer ligands, pyridine-2,6-diylbis(diphenylphosphino)methanone, 2,6-{Ph2PC(O)}2(C5H3N) (1) (hereafter referred to as "bis(phosphomide)"), was prepared by the reaction of picolinoyldichloride with diphenylphosphine in the presence of triethylamine. The bis(phosphomide) 1 shows symmetrical PNP, unsymmetrical PNO and simple bidentate PP coordination modes when treated with various transition metal precursors. The reaction between 1 and [Ru(p-cymene)Cl2]2 in a 1 : 1 molar ratio yielded a binuclear complex [Ru2Cl4(NCCH3)(p-cymene){2,6-{Ph2PC(O)}2(C5H3N)}] (2) containing an unsymmetrical PNO pincer cage around one of the ruthenium centers, whereas the second ruthenium is bonded to the other phosphorus atom along with cymene and two chloride atoms. Symmetrical pincer complexes [RuCl(NCCH3)2{2,6-{Ph2PC(O)}2(C5H3N)}](ClO4) (3), [Ru(η(5)-C5H5){2,6-{Ph2PC(O)}2(C5H3N)}](OTf) (4) and [RhCl{2,6-{Ph2PC(O)}2(C5H3N)}] (5) were obtained in the respective reactions of 1 with [RuCl(NCCH3)2(p-cymene)](ClO4), [Ru(η(5)-C5H5)Cl(PPh3)2] and [Rh(COD)Cl]2. Group 10 metal complexes [NiCl{2,6-{Ph2PC(O)}2(C5H3N)}](BF4) (6), [PdCl{2,6-{Ph2PC(O)}2(C5H3N)}]ClO4 (7) and [PtCl{2,6-{Ph2PC(O)}2(C5H3N)}]ClO4 (8) were obtained by transmetallation reactions of in situ generated Ag(I) salts of 1 with Ni(DME)Cl2 or M(COD)Cl2 (M = Ni, Pd and Pt). The reactions between 1 and CuX or [Cu(NCCH3)4](BF4) produced mononuclear complexes of the type [CuX{2,6-{Ph2PC(O)}2(C5H3N)}] (9, X = Cl; 10, X = Br; 11, X = I), [Cu(NCCH3){Ph2C(O)}2(C5H3N)}](BF4) (12) and [Cu{Ph2C(O)}2(C5H3N)}2](BF4) (13). Similarly, the silver complexes [AgX{2,6-{Ph2PC(O)}2(C5H3N)}] (14, X = ClO4; 15, X = Br) were obtained by the treatment of 1 with AgClO4 or AgBr in 1 : 1 molar ratios. Treatment of 1 with AuCl(SMe2) in 1 : 1 and 1 : 2 molar ratios produced mono- and binuclear complexes, [AuCl{2,6-{Ph2PC(O)}2(C5H3N)}] (16) and [Au2Cl2{2,6-{Ph2PC(O)}2(C5H3N)}] (17), in good yield. The structures of ligand 1 and complexes 2, 5 and 17 were confirmed using single-crystal X-ray diffraction studies. DFT calculations were carried out to gain more insights into the structure and bonding features as well as feasibility of some key chemical transformations.