Robert Howard Grubbs

Macrocyclic polyalkenamers formed as byproducts during ring-opening metathesis polymerization (ROMP) provide valuable insight into ring–chain equilibria and secondary metathesis processes. However, the characterization of these macrocycles is often complicated by the presence of linear polymer products with identical chemical composition. Here, we present a strategy to facilitate the isolation of macrocycles generated during ROMP by modifying chain ends using enyne metathesis chemistry and introducing polar functional groups into linear polymer chains through the addition of polar monomers. The resulting polarity difference allows nonpolar macrocycles to be separated from linear polymers by using conventional silica gel chromatography. The isolated cyclic fractions were characterized by gel permeation chromatography (GPC), NMR spectroscopy, and matrix-assisted laser desorption-ionization time-of-flight mass spectrometry (MALDI-TOF MS). Using this approach, we systematically investigated how reaction parameters influence the yield and molecular weight of macrocycles in the ROMP of cyclooctadiene (COD). The methodology also enables comparative analysis of macrocycle formation in the ROMP of cyclooctene (COE), cyclopentene (CP), and norbornene (NB). These results provide a separation-based approach for studying the macrocyclic species formed during ROMP.

Cyclopolymerization is a powerful method for synthesizing polyacetylenes containing four‐ to seven‐membered rings. However, the structure of the repeat unit only consists of mono‐cycloalkene due to the single cyclization of diyne monomers. Herein, we demonstrate a novel cascade cyclopolymerization to synthesize polyacetylenes containing fused bicyclic rings from triyne monomers containing bulky dendrons via sequential cascade ring‐closing metathesis. These dendrons provided solubility and stability to the rigid bicyclic polyacetylene backbone. In addition, we controlled the regioselectivity of the catalyst approach by altering its structure and synthesized polymers containing fused bicyclo[4,3,0] or [4,4,0] rings with high molecular weights of up to 120 kg mol⁻¹. Interestingly, the resulting polymers showed narrower band gaps (down to 1.6 eV) than polymers with mono‐cycloalkene repeat units due to the planarization of the conjugated segment resulting from the fused bicyclic structure.

Cyclopolymerization is a powerful method for synthesizing polyacetylenes containing four‐ to seven‐membered rings. However, the structure of the repeat unit only consists of mono‐cycloalkene due to the single cyclization of diyne monomers. Herein, we demonstrate a novel cascade cyclopolymerization to synthesize polyacetylenes containing fused bicyclic rings from triyne monomers containing bulky dendrons via sequential cascade ring‐closing metathesis. These dendrons provided solubility and stability to the rigid bicyclic polyacetylene backbone. In addition, we controlled the regioselectivity of the catalyst approach by altering its structure and synthesized polymers containing fused bicyclo[4,3,0] or [4,4,0] rings with high molecular weights of up to 120 kg mol⁻¹. Interestingly, the resulting polymers showed narrower band gaps (down to 1.6 eV) than polymers with mono‐cycloalkene repeat units due to the planarization of the conjugated segment resulting from the fused bicyclic structure.

A concise and stereoselective total synthesis of the clinically relevant tricyclic prostaglandin D₂ metabolite (tricyclic‐PGDM) methyl ester in racemic form was accomplished in eight steps from a readily available known cyclopentene‐diol derivative. The synthesis features a nickel‐catalyzed Ueno–Stork‐type dicarbofunctionalization to generate two consecutive stereocenters, a palladium‐catalyzed carbonylative spirolactonization to build the core oxaspirolactone, and a Z‐selective cross‐metathesis to introduce the (Z)‐3‐butenoate side chain, a group challenging to introduce through traditional Wittig protocols and troublesome for the two previous total syntheses. A general Z‐selective cross‐metathesis protocol to construct (Z)‐β,γ‐unsaturated esters was also developed that has broad functional group tolerance and high stereoselectivity. Additionally, our synthesis already accumulated 75 mg of valuable material for an ¹⁸O‐tricyclic‐PGDM‐based assay used in clinical settings for inflammation.

A concise and stereoselective total synthesis of the clinically relevant tricyclic prostaglandin D₂ metabolite (tricyclic‐PGDM) methyl ester in racemic form was accomplished in eight steps from a readily available known cyclopentene‐diol derivative. The synthesis features a nickel‐catalyzed Ueno–Stork‐type dicarbofunctionalization to generate two consecutive stereocenters, a palladium‐catalyzed carbonylative spirolactonization to build the core oxaspirolactone, and a Z‐selective cross‐metathesis to introduce the (Z)‐3‐butenoate side chain, a group challenging to introduce through traditional Wittig protocols and troublesome for the two previous total syntheses. A general Z‐selective cross‐metathesis protocol to construct (Z)‐β,γ‐unsaturated esters was also developed that has broad functional group tolerance and high stereoselectivity. Additionally, our synthesis already accumulated 75 mg of valuable material for an ¹⁸O‐tricyclic‐PGDM‐based assay used in clinical settings for inflammation.

α‐Oxygenated Z‐olefins are ubiquitous in biologically active molecules and serve as versatile handles for organic synthesis, but their syntheses are often tedious and less selective. Here we report the efficient Z‐selective metathesis of various terminal acrylates and allyl alcohols, which enables facile and selective construction of high value‐added α‐oxygenated Z‐olefins from readily available feedstock chemicals. These challenging metathesis transformations are enabled by novel cyclometalated Ru‐carbene‐nitrate complexes bearing bulky‐yet‐flexible side arms, whose assembly was unlocked by new organometallic syntheses.

α‐Oxygenated Z‐olefins are ubiquitous in biologically active molecules and serve as versatile handles for organic synthesis, but their syntheses are often tedious and less selective. Here we report the efficient Z‐selective metathesis of various terminal acrylates and allyl alcohols, which enables facile and selective construction of high value‐added α‐oxygenated Z‐olefins from readily available feedstock chemicals. These challenging metathesis transformations are enabled by novel cyclometalated Ru‐carbene‐nitrate complexes bearing bulky‐yet‐flexible side arms, whose assembly was unlocked by new organometallic syntheses.

The self-assembly of poly(dimethylsiloxane)-b-poly(trimethylene carbonate) (PDMS-b-PTMC) bottlebrush block polymers was investigated under different processing conditions. Small-angle X-ray scattering (SAXS) and UV/Visible spectroscopy provided insight into the self-assembly and structure in response to heating and applied pressure. In the absence of applied pressure (i.e., before annealing), the PDMS-b-PTMC bottlebrush block polymers are white solids and adopt small, randomly oriented lamellar grains. Heating the materials to 140 °C in the absence of applied pressure appears to “lock in” the isotropic, short-range-ordered state, preventing the formation of the long-range-ordered lamellar structure responsible for photonic properties. Applying modest anisotropic pressure (3 psi) between parallel plates at ambient temperature orients the short-range lamellar grains; however, applied pressure alone does not produce long-range order. Only when the bottlebrush block polymers were heated (>100 °C) under modest pressure (3 psi) were long-range-ordered photonic crystals formed. Analysis of the SAXS data motivated analogies to liquid crystals and revealed the potential self-assembly pathway. These results provide insight into the structure and self-assembly of bottlebrush block polymers with low glass transition temperature side chains in response to different processing conditions.

Electrochemical CO₂ reduction over Cu could provide value-added multicarbon hydrocarbons and alcohols. Despite recent breakthroughs, it remains a significant challenge to design a catalytic system with high product selectivity. Here we demonstrate that a high selectivity of ethylene (55%) and C₂₊ products (77%) could be achieved by a highly modular tricomponent copolymer modified Cu electrode, rivaling the best performance using other modified polycrystalline Cu foil catalysts. Such a copolymer can be conveniently prepared by a ring-opening metathesis polymerization, thereby offering a new degree of freedom for tuning the selectivity. Control experiments indicate all three components are essential for the selectivity enhancement. A surface characterization showed that the incorporation of a phenylpyridinium component increased the film robustness against delamination. It was also shown that its superior performance is not due to a morphology change of the Cu underneath. Molecular dynamics (MD) simulations indicate that a combination of increased local CO₂ concentration, increased porosity for gas diffusion, and the local electric field effect together contribute to the increased ethylene and C₂₊ product selectivity.