http://www.rssboard.org/rss-specification 720 https://escholarship.org/uc/nobel_m2005_schrock/rss Recent eScholarship items from Richard R. Schrock, UC Riverside (Nobel Prize in Chemistry, 2005) Sun, 20 Sep 2026 20:06:00 +0000 https://escholarship.org/uc/item/6n74w2s1 All animals except sponges produce mucus. Across the animal kingdom, this hydrogel mediates surface wetting, viscosity, and protection against microbes. The primary components of mucus hydrogels are mucins-high molecular weight <i>O</i>-glycoproteins that adopt extended linear structures. Glycosylation is integral to mucin function, but other characteristics that give rise to their advantageous biological activities are unknown. We postulated that the extended conformation of mucins is critical for their ability to block microbial virulence phenotypes. To test this hypothesis, we developed synthetic mucin mimics that recapitulate the dense display of glycans and morphology of mucin. We varied the catalyst in a ring-opening metathesis polymerization (ROMP) to generate substituted norbornene-derived glycopolymers containing either cis- or trans-alkenes. Conformational analysis of the polymers based on allylic strain suggested that cis- rather than trans-poly(norbornene) glycopolymers... https://escholarship.org/uc/item/6n74w2s1 Mon, 7 Jun 2021 00:00:00 +0000 Kruger, Austin G Brucks, Spencer D Yan, Tao Cárcarmo-Oyarce, Gerardo Wei, Yuan Wen, Deborah H Carvalho, Dayanne R Hore, Michael JA Ribbeck, Katharina Schrock, Richard R https://orcid.org/0000-0001-5827-3552 Kiessling, Laura L https://escholarship.org/uc/item/9nh1t0x2 Ring-closing metathesis is a widely used chemical transformation that can generate organic macrocycle compounds; here, an approach is described by which the E-stereoisomer of a macrocycle is generated selectively, exemplified by synthesizing the antibiotic recifeolide and the anti-cancer drug pacritinib. https://escholarship.org/uc/item/9nh1t0x2 Mon, 12 Oct 2020 00:00:00 +0000 Shen, Xiao Nguyen, Thach T Koh, Ming Joo Xu, Dongmin Speed, Alexander WH Schrock, Richard R https://orcid.org/0000-0001-5827-3552 Hoveyda, Amir H https://escholarship.org/uc/item/95m459cg Imido alkylidene complexes of Mo and W and oxo alkylidene complexes of W that contain thiophenoxide ligands of the type S-2,3,5,6-Ph₄C₆H (STPP) and S-2,6-(mesityl)₂C₆H₃ (SHMT = S-hexamethylterphenyl) have been prepared in order to compare their metathesis activity with that of the analogous phenoxide complexes. All thiolate complexes were significantly slower (up to ∼10× slower) for the metathesis homocoupling of 1-octene or polymerization of 2,3-dicarbomethoxynorbornene, and none of them was <i>Z</i>-selective. The slower rates could be attributed to the greater σ-donating ability of a thiophenoxide versus the analogous phenoxide and consequently a higher electron density at the metal in the thiophenoxide complexes. https://escholarship.org/uc/item/95m459cg Mon, 12 Oct 2020 00:00:00 +0000 Townsend, Erik M Hyvl, Jakub Forrest, William P Schrock, Richard R https://orcid.org/0000-0001-5827-3552 Müller, Peter Hoveyda, Amir H https://escholarship.org/uc/item/8r10399r Biological nitrogen fixation is enabled by molybdenum-dependent nitrogenase enzymes, which effect the reduction of dinitrogen to ammonia using an Fe7MoS9C active site, referred to as the iron molybdenum cofactor or FeMoco. In this mini-review, we summarize the current understanding of the molecular and electronic structure of FeMoco. The advances in our understanding of the active site structure are placed in context with the parallel evolution of synthetic model studies. The recent discovery of Mo(III) in the FeMoco active site is highlighted with an emphasis placed on the important role that model studies have played in this finding. In addition, the reactivities of synthetic models are discussed in terms of their relevance to the enzymatic system. https://escholarship.org/uc/item/8r10399r Mon, 12 Oct 2020 00:00:00 +0000 Bjornsson, Ragnar Neese, Frank Schrock, Richard R https://orcid.org/0000-0001-5827-3552 Einsle, Oliver DeBeer, Serena https://escholarship.org/uc/item/82g6n7bx The first examples of catalyst-controlled stereoselective macrocyclic ring-closing metathesis reactions that generate Z-enoates as well as (E,Z)- or (Z,E)-dienoates are disclosed. Reactions promoted by 3.0-10 mol % of a Mo-based monoaryloxide pyrrolide complex proceed to completion within 2-6 h at room temperature. The desired macrocycles are formed in 79:21 to &gt;98:2 Z/E selectivity; stereoisomerically pure products can be obtained in 43-75% yield after chromatography. Utility is demonstrated by application to a concise formal synthesis of the natural product (+)-aspicilin. https://escholarship.org/uc/item/82g6n7bx Mon, 12 Oct 2020 00:00:00 +0000 Zhang, Hanmo Yu, Elsie C Torker, Sebastian Schrock, Richard R https://orcid.org/0000-0001-5827-3552 Hoveyda, Amir H https://escholarship.org/uc/item/30g758vh Catalytic cross-metathesis is a central transformation in chemistry, yet corresponding methods for the stereoselective generation of acyclic trisubstituted alkenes in either the E or the Z isomeric forms are not known. The key problems are a lack of chemoselectivity—namely, the preponderance of side reactions involving only the less hindered starting alkene, resulting in homo-metathesis by-products—and the formation of short-lived methylidene complexes. By contrast, in catalytic cross-coupling, substrates are more distinct and homocoupling is less of a problem. Here we show that through cross-metathesis reactions involving E- or Z-trisubstituted alkenes, which are easily prepared from commercially available starting materials by cross-coupling reactions, many desirable and otherwise difficult-to-access linear E- or Z-trisubstituted alkenes can be synthesized efficiently and in exceptional stereoisomeric purity (up to 98 per cent E or 95 per cent Z). The utility of the strategy... https://escholarship.org/uc/item/30g758vh Mon, 12 Oct 2020 00:00:00 +0000 Nguyen, Thach T Koh, Ming Joo Mann, Tyler J Schrock, Richard R https://orcid.org/0000-0001-5827-3552 Hoveyda, Amir H https://escholarship.org/uc/item/25n288td A convergent diastereo- and enantioselective total synthesis of anticancer and antifungal macrocyclic natural product disorazole C1 is reported. The central feature of the successful route is the application of catalytic Z-selective cross-metathesis (CM). Specifically, we illustrate that catalyst-controlled stereoselective CM can be performed to afford structurally complex Z-alkenyl-B(pin) as well as Z-alkenyl iodide compounds reliably, efficiently, and with high selectivity (pin = pinacolato). The resulting intermediates are then joined in a single-step operation through catalytic inter- and intramolecular cross-coupling to furnish the desired 30-membered ring macrocycle containing the critical (Z,Z,E)-triene moieties. https://escholarship.org/uc/item/25n288td Mon, 12 Oct 2020 00:00:00 +0000 Speed, Alexander WH Mann, Tyler J O’Brien, Robert V Schrock, Richard R https://orcid.org/0000-0001-5827-3552 Hoveyda, Amir H https://escholarship.org/uc/item/24q1t30z One shortcoming of olefin metathesis has been that acyclic alkenyl halides could not be generated efficiently and stereoselectively; but now halo-substituted molybdenum alkylidene species are shown to be able to participate in high-yielding olefin metathesis reactions that afford acyclic 1,2-disubstituted Z-alkenyl halides. https://escholarship.org/uc/item/24q1t30z Mon, 12 Oct 2020 00:00:00 +0000 Koh, Ming Joo Nguyen, Thach T Zhang, Hanmo Schrock, Richard R https://orcid.org/0000-0001-5827-3552 Hoveyda, Amir H https://escholarship.org/uc/item/1df815bd <i>Cis</i>,<i>syndiotactic</i><b>A</b>-<i>alt</i>-<b>B</b> copolymers, where <b>A</b> and <b>B</b> are two enantiomerically pure <i>trans</i>-2,3-disubstituted-5,6-norbornenes with "opposite" chiralities, can be prepared with stereogenic-at-metal initiators of the type M(NR)(CHR')(OR")(pyrrolide). Formation of a high percentage of alternating <b>AB</b> copolymer linkages relies on an inversion of chirality at the metal with each propagating step and a relatively fast formation of an <b>AB</b> sequence as a consequence of a preferred diastereomeric relationship between the chirality at the metal and the chirality of the monomer. This approach to formation of an alternating <b>AB</b> copolymer contrasts dramatically with the principle of forming <b>AB</b> copolymers from achiral monomers and catalysts. https://escholarship.org/uc/item/1df815bd Mon, 12 Oct 2020 00:00:00 +0000 Jang, Eun Sil John, Jeremy M Schrock, Richard R https://orcid.org/0000-0001-5827-3552 https://escholarship.org/uc/item/0x03k3q2 Nitriles are found in many bioactive compounds, and are among the most versatile functional groups in organic chemistry. Despite many notable recent advances, however, there are no approaches that may be used for the preparation of di- or tri-substituted alkenyl nitriles. Related approaches that are broad in scope and can deliver the desired products in high stereoisomeric purity are especially scarce. Here, we describe the development of several efficient catalytic cross-metathesis strategies, which provide direct access to a considerable range of Z- or E-di-substituted cyano-substituted alkenes or their corresponding tri-substituted variants. Depending on the reaction type, a molybdenum-based monoaryloxide pyrrolide or chloride (MAC) complex may be the optimal choice. The utility of the approach, enhanced by an easy to apply protocol for utilization of substrates bearing an alcohol or a carboxylic acid moiety, is highlighted in the context of applications to the synthesis of... https://escholarship.org/uc/item/0x03k3q2 Mon, 12 Oct 2020 00:00:00 +0000 Mu, Yucheng Nguyen, Thach T Koh, Ming Joo Schrock, Richard R https://orcid.org/0000-0001-5827-3552 Hoveyda, Amir H https://escholarship.org/uc/item/03f7s6fj Tungsten NAr^R alkylidene complexes have been prepared that contain the electron-withdrawing Ar^R groups 2,4,6-X₃C₆H₂ (Ar^X3, X = Cl, Br), 2,6-Cl₂-4-CF₃C₆H₂ (Ar^Cl2CF3), and 3,5-(CF₃)₂C₆H₃ (Ar^(CF3)2). Reported complexes include W(NAr^R)₂Cl₂(dme) (dme = 1,2-dimethoxyethane), W(NAr^R)₂(CH₂CMe₃)₂, W(NAr^R)(CHCMe₃)(OTf)₂(dme), and W(NAr^R)(CHCMe₃)(ODBMP)₂ (DBMP = 4-Me-2,6-(CHPh₂)C₆H₂). The W(NAr^R)(CHCMe₃)(ODBMP)₂ complexes were explored as initiators for the polymerization of 2,3-dicarbomethoxynorbornadiene (DCMNBD). https://escholarship.org/uc/item/03f7s6fj Mon, 12 Oct 2020 00:00:00 +0000 Axtell, Jonathan C Schrock, Richard R https://orcid.org/0000-0001-5827-3552 Müller, Peter Smith, Stacey J Hoveyda, Amir H https://escholarship.org/uc/item/46m4c09b 3,3′,5,5′-Tetra-tert-butyl-2′-sulfanyl[1,1′-biphenyl]-2-ol (H2[tBu4OS]) was prepared in 24 % yield overall from the analogous biphenol using standard techniques. Addition of H2[tBu4OS] to Mo(NAr)(CHCMe2Ph)(2,5-dimethylpyrrolide)2 led to formation of Mo(NAr)(CHCMe2Ph)[tBu4OS], which was trapped with PMe3 to give Mo(NAr)(CHCMe2Ph)[tBu4OS](PMe3) (1(PMe3)). An X-ray crystallographic study of 1(PMe3) revealed that two structurally distinct square pyramidal molecules are present in which the alkylidene ligand occupies the apical position in each. Both 1(PMe3)A and 1(PMe3)B are disordered. Mo(NAd)(CHCMe2Ph)(tBu4OS)(PMe3) (2(PMe3); Ad=1-adamantyl) and W(NAr)(CHCMe2Ph)(tBu4OS)(PMe3) (3(PMe3)) were prepared using analogous approaches. 1(PMe3) reacts with ethylene (1 atm) in benzene within 45 minutes to give an ethylene complex Mo(NAr)(tBu4OS)(C2H4) (4) that is isolable and relatively stable toward loss of ethylene below 60 °C. An X-ray study shows that the bond distances and angles for... https://escholarship.org/uc/item/46m4c09b Wed, 10 Jun 2020 00:00:00 +0000 Tafazolian, Hosein VenkatRamani, Sudarsan Tsay, Charlene Schrock, Richard R https://orcid.org/0000-0001-5827-3552 Müller, Peter https://escholarship.org/uc/item/3cb4610z Mo(C-t-Bu)(CH-t-Bu)(Cl)(PMe2Ph)2 (1) was prepared as off-white crystals in 26% yield through addition of 2.5 equiv of Mg(CH2-t-Bu)2 to Mo(O)[OC(CF3)3]4 in diethyl ether followed by 3 equiv of PMe2Ph and a workup that includes dichloromethane (the source of Cl). Compound 1 is largely a syn isomer initially that equilibrates to give approximately a 1:1 mixture of syn and anti isomers within 1-2 h. Compound 1 reacts with Li(3,5-dimethylpyrrolide) to give Mo(C-t-Bu)(CH-t-Bu)(η1-Me2Pyr)(PMe2Ph)2 (2a) as a pale yellow solid in 76% yield, and 2a reacts with Ph3SiOH to give a mixture of syn and anti Mo(C-t-Bu)(CH-t-Bu)(OSiPh3)(PMe2Ph)2 (3a) in 84% yield. All three compounds tend to lose PMe2Ph to give 14e monophosphine complexes with the formulas Mo(C-t-Bu)(CH-t-Bu)(X)(PMe2Ph) (X = Cl, Me2Pyr, or OSiPh3), none of which could be isolated. X-ray studies show the structures of 1, 2a, and 3a to be analogous with τ values of 0.45, 0.53, and 0.69, respectively. https://escholarship.org/uc/item/3cb4610z Wed, 10 Jun 2020 00:00:00 +0000 Tafazolian, Hosein Schrock, Richard R https://orcid.org/0000-0001-5827-3552 Müller, Peter https://escholarship.org/uc/item/30s6k6g6 Through relatively straightforward techniques that begin with Mo(NAr)(CH-t-Bu)[OCMe(CF3)2]2 (Ar = 2,6-i-Pr2C6H3), we have prepared Mo(NAr)(CMePh)(OMesityl)2, [Mo(NAr)(CMePh)(OC6F5)2]2, Mo(NAr)(CMePh)(OC6F5)2(MeCN), Mo(NAr)(CMePh)(OC6F5)2(bipyridyl), Mo(NAr)(CMePh)(Cl)2(bipyridyl), Mo(NAr)(CMePh)(Cl)(OHMT)(MeCN) (OHMT = O-2,6-(2,4,6-Me3C6H2)2C6H3), and Mo(NAr)(CMePh)(Pyrrolide)(OHMT). X-ray studies reveal that in five compounds the alkylidene isomer (A) is that in which the phenyl group in the alkylidene points toward the imido nitrogen. In Mo(NAr)(CMePh)(OC6F5)2(MeCN) the isomer in which the methyl group points toward the imido nitrogen (isomer B) has cocrystallized with isomer A (12%). In two 14e compounds that contain isomer A, the Mo═C-C angles differ by 30-36°, consistent with a Mo...C-Hβ agostic interaction. Several of the complexes reported here react readily with ethylene, 1-decene, or cyclooctene to give the expected products, thus confirming their viability as initiators... https://escholarship.org/uc/item/30s6k6g6 Wed, 10 Jun 2020 00:00:00 +0000 Taylor, Jordan W Schrock, Richard R https://orcid.org/0000-0001-5827-3552 Tsay, Charlene