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.

A dithienylethene-functionalized N-heterocyclic carbene-Ru(II) complex was synthesized and found to undergo a reversible photoisomerization which influenced its intrinsic catalytic activity. UV-induced ring-closure enhanced the rate of ringclosing metathesis reactions (k closed /k opened = 1.4−1.7) and attenuated the rate of ring-opening metathesis polymerizations (k closed /k opened = 0.56−0.66). Visible light irradiation promoted cycloreversion and restored the initial activity. The ability to switch between the isomeric states of the catalyst was also utilized to modulate the rate of ongoing olefin metathesis reactions via photoirradiation. A computational investigation revealed how steric and electronic effects separately influence the transition states adopted by each form of the catalyst and afforded activation energies that were in agreement with the relative reaction rate constants determined by experiment.

Enantioenriched α-aminoboronic acids play a unique role in medicinal chemistry and have emerged as privileged pharmacophores in proteasome inhibitors. Additionally, they represent synthetically useful chiral building blocks in organic synthesis. Recently, CuH-catalyzed asymmetric alkene hydrofunctionalization has become a powerful tool to construct stereogenic carbon centers. In contrast, applying CuH cascade catalysis to achieve reductive 1,1difunctionalization of alkynes remains an important, but largely unaddressed, synthetic challenge. Herein, we report an efficient strategy to synthesize α-aminoboronates via CuH-catalyzed hydroboration/hydroamination cascade of readily available alkynes. Notably, this transformation selectively delivers the desired 1,1-heterodifunctionalized product in favor of alternative homodifunctionalized, 1,2-heterodifunctionalized, or reductively monofunctionalized byproducts, thereby offering rapid access to these privileged scaffolds with high chemo-, regio-and enantioselectivity. Alkenes and alkynes are ideal starting materials in organic synthesis due to the fact that they can be readily prepared using a variety of convenient synthetic methods and are widely available from commercial suppliers. Catalytic functionalization of the π-bonds in these substrates leads to a valuable array of building blocks and in the case of alkenes offers a Users may view, print, copy, and download text and data-mine the content in such documents, for the purposes of academic research, subject always to the full Conditions of use:

Skeletal ring enlargement is gaining renewed interest in synthetic chemistry and has recently focused on insertion of one or two atoms. Strategies for heterocyclic expansion through small-ring insertion remain elusive, although they would lead to the efficient formation of bicyclic products. Here, we report a photoinduced dearomative ring enlargement of thiophenes by insertion of bicyclo[1.1.0]butanes to produce eight-membered bicyclic rings under mild conditions. The synthetic value, broad functional-group compatibility, and excellent chemo- and regioselectivity were demonstrated by scope evaluation and product derivatization. Experimental and computational studies point toward a photoredox-induced radical pathway.

A ring-opening metathesis polymerization catalyst supported by a redox-active N-heterocyclic carbene was synthesized and found to undergo reversible reduction. In its neutral form, the catalyst polymerized 1,5-cis,cis-cyclooctadiene at a higher rate than that of a norbornene derivative; however, upon reduction, the selectivity was found to reverse. Utilizing this oxidation state dependent selectivity, a series of copolymers with controlled compositions, microstructures, and physical properties were prepared by redox-switching the catalyst over the course of a series of polymerization reactions.

A comprehensive computational study of stereoretentive olefin metathesis with Rudithiolate catalysts has been performed. We have determined how the dithiolate ligand enforces a side-bound mechanism and how the side-bound mechanism allows for stereochemical control over the forming olefin. We have used density functional theory (DFT) and ligand steric contour maps to elucidate the origins of stereoretentive metathesis with the goal of understanding how to design a new class of E-selective metathesis catalysts.

A ring-closing metathesis catalyst was arrested upon reduction of a redox-active ligand; subsequent oxidation restored catalytic activity.

Copolymerization of CO2 and cyclohexene oxide (CHO) upcycles CO2 into the value-added, chemically recyclable, thermoplastic poly­(cyclohexene carbonate) (PCHC). Using density functional theory, the Zn-catalyzed copolymerization mechanism has been characterized with a particular focus on the effects of chiral β-diiminate (BDI) ligands as they influence the reactivity and enantioselectivity in the epoxide ring-opening step, where the latter is required for isotacticity. Theory indicates that both mono- and binuclear forms of the catalyst are involved along the reaction path, with the turnover-limiting step being ring-opening of the epoxide mediated by a binuclear catalyst. Subsequent CO2 insertion is predicted to be kinetically facile and preferentially mediated by a mononuclear catalyst. The predicted preference for epoxide opening to give R,R-stereocenters in the copolymer when N-(4-(((1S,2S)-2-(benzyloxy)­cyclohexyl)­amino)-5,5,5-trifluoropent-3-en-2-ylidene)-2,6-dimethylaniline is used as the BDI ligand agrees with the experiment and is attributed to differential ligand distortions associated with key non-bonded interactions in the competing transition-state structures. Further analysis predicts that 2,6-dichloro and dibromo substitutions of the BDI ligand N-aryl group(s) should result in increased rates and enantioselectivities for copolymerization.