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Alois Furstner - One of the best experts on this subject based on the ideXlab platform.

  • the ascent of Alkyne Metathesis to strategy level status
    Journal of the American Chemical Society, 2021
    Co-Authors: Alois Furstner
    Abstract:

    For numerous enabling features and strategic virtues, contemporary Alkyne Metathesis is increasingly recognized as a formidable synthetic tool. Central to this development was the remarkable evolution of the catalysts during the past decades. Molybdenum alkylidynes carrying (tripodal) silanolate ligands currently set the standards; their functional group compatibility is exceptional, even though they comprise an early transition metal in its highest oxidation state. Their performance is manifested in case studies in the realm of dynamic covalent chemistry, advanced applications to solid-phase synthesis, a revival of transannular reactions, and the assembly of complex target molecules at sites, which one may not intuitively trace back to an acetylenic ancestor. In parallel with these innovations in material science and organic synthesis, new insights into the mode of action of the most advanced catalysts were gained by computational means and the use of unconventional analytical tools such as 95Mo and 183W NMR spectroscopy. The remaining shortcomings, gaps, and desiderata in the field are also critically assessed.

  • canopy catalysts for Alkyne Metathesis investigations into a bimolecular decomposition pathway and the stability of the podand cap
    Chemistry: A European Journal, 2021
    Co-Authors: Julius Hillenbrand, Markus Leutzsch, Nils Nothling, Nepomuk J Korber, Alois Furstner
    Abstract:

    Molybdenum alkylidyne complexes with a trisilanolate podand ligand framework ("canopy catalysts") are the arguably most selective catalysts for Alkyne Metathesis known to date. Among them, complex 1 a endowed with a fence of lateral methyl substituents on the silicon linkers is the most reactive, although fairly high loadings are required in certain applications. It is now shown that this catalyst decomposes readily via a bimolecular pathway that engages the Mo≡CR entities in a stoichiometric triple-bond Metathesis event to furnish RC≡CR and the corresponding dinuclear complex, 8, with a Mo≡Mo core. In addition to the regular analytical techniques, 95 Mo NMR was used to confirm this unusual outcome. This rapid degradation mechanism is largely avoided by increasing the size of the peripheral substituents on silicon, without unduly compromising the activity of the resulting complexes. When chemically challenged, however, canopy catalysts can open the apparently somewhat strained tripodal ligand cages; this reorganization leads to the formation of cyclo-tetrameric arrays composed of four metal alkylidyne units linked together via one silanol arm of the ligand backbone. The analogous tungsten alkylidyne complex 6, endowed with a tripodal tris-alkoxide (rather than siloxide) ligand framework, is even more susceptible to such a controlled and reversible cyclo-oligomerization. The structures of the resulting giant macrocyclic ensembles were established by single-crystal X-ray diffraction.

  • an Alkyne Metathesis based approach to the synthesis of the anti malarial macrodiolide samroiyotmycin a
    Angewandte Chemie, 2021
    Co-Authors: Ektoras Yiannakas, Alois Furstner, Mark Grimes, James Whitelegge, Alison N Hulme
    Abstract:

    We report the first total synthesis of samroiyotmycin A (1), a C2-symmetric 20-membered anti-malarial macrodiolide isolated from Streptomyces sp. The convergent synthetic strategy orchestrates bisAlkyne fragment-assembly using an unprecedented Schӧllkopf-type condensation on a substituted β-lactone and an ambitious late-stage one-pot Alkyne cross Metathesis - ring-closing Metathesis (ACM-RCAM) reaction. The demanding Alkyne Metathesis sequence is achieved using the latest generation of molybdenum alkylidynes endowed with a tripodal silanolate ligand framework. Subsequent conversion to the required E-alkenes uses contemporary hydrometallation chemistry catalysed by tetrameric cluster [{Cp*RuCl}4].

  • productive Alkyne Metathesis with canopy catalysts mandates pseudorotation
    Journal of the American Chemical Society, 2021
    Co-Authors: Alexander Haack, Julius Hillenbrand, Markus Leutzsch, Maurice Van Gastel, Frank Neese, Alois Furstner
    Abstract:

    Molybdenum alkylidyne complexes of the “canopy catalyst” series define new standards in the field of Alkyne Metathesis. The tripodal ligand framework lowers the symmetry of the metallacyclobutadien...

  • 183 w nmr spectroscopy guides the search for tungsten alkylidyne catalysts for Alkyne Metathesis
    Angewandte Chemie, 2020
    Co-Authors: Julius Hillenbrand, Markus Leutzsch, Christopher P Gordon, Christophe Coperet, Alois Furstner
    Abstract:

    Triarylsilanolates are privileged ancillary ligands for molybdenum alkylidyne catalysts for Alkyne Metathesis but lead to disappointing results and poor stability in the tungsten series. 1H,183W Heteronuclear Multiple Bond Correlation (HMBC) spectroscopy exploiting a favorable 5J-coupling between the 183W center and the peripheral protons on the alkylidyne cap revealed that these ligands upregulate the Lewis-acidity to an extent that the tungstenacyclobutadiene formed in the initial [2+2] cycloaddition step is over-stabilized and the catalytic turnover brought to a hold. The metallacycle itself does exist in two tautomeric forms and must not be mistaken for a mesomeric resonance extreme, as evident from spectroscopic and crystallographic data. Guided by the 183W NMR shifts as a proxy for the Lewis acidity of the central atom and an accompanying chemical shift tensor analysis of the alkylidyne unit, the ligand design was revisited and a more strongly π-donating all-alkoxide ligand prepared. The new "expanded" chelate complex has a tempered Lewis-acidity and outperforms the classical Schrock catalyst carrying monodentate tert-butoxy ligands in terms of rate and functional group compatibility.

Wei Zhang - One of the best experts on this subject based on the ideXlab platform.

  • highly active Alkyne Metathesis catalysts operating under open air condition
    Nature Communications, 2021
    Co-Authors: Shaofeng Huang, Yinghua Jin, Lei Zhang, Sebastian M Krajewski, Michael Ortiz, Wei Zhang
    Abstract:

    Alkyne Metathesis represents a rapidly emerging synthetic method that has shown great potential in small molecule and polymer synthesis. However, its practical use has been impeded by the limited availability of user-friendly catalysts and their generally high moisture/air sensitivity. Herein, we report an Alkyne Metathesis catalyst system that can operate under open-air conditions with a broad substrate scope and excellent yields. These catalysts are composed of simple multidentate tris(2-hydroxyphenyl)methane ligands, which can be easily prepared in multi-gram scale. The catalyst substituted with electron withdrawing cyano groups exhibits the highest activity at room temperature with excellent functional group tolerance (-OH, -CHO, -NO2, pyridyl). More importantly, the catalyst provides excellent yields (typically >90%) in open air, comparable to those operating under argon. When dispersed in paraffin wax, the active catalyst can be stored on a benchtop under ambient conditions without any decrease in activity for one day (retain 88% after 3 days). This work opens many possibilities for developing highly active user-friendly Alkyne Metathesis catalysts that can function in open air.

  • highly active multidentate ligand based Alkyne Metathesis catalysts
    ChemInform, 2016
    Co-Authors: Haishen Yang, Yinghua Jin, Michael Ortiz, Chengpu Zhu, Kenji D Okochi, Richard K Shoemaker, Wei Zhang
    Abstract:

    Alkyne Metathesis catalysts composed of molybdenum(VI) propylidyne and multidentate tris(2-hydroxylbenzyl)methane ligands have been developed, which exhibit excellent stability (remains active in solution for months at room temperature), high activity, and broad functional-group tolerance. The homodimerization and cyclooligomerization of monopropynyl or dipropynyl substrates, including challenging heterocycle substrates (e.g., pyridine), proceed efficiently at 40-55 °C in a closed system. The ligand structure and catalytic activity relationship has been investigated, which shows that the ortho groups of the multidentate phenol ligands are critical to the stability and activity of such a catalyst system.

  • synthesis of cyclic porphyrin trimers through Alkyne Metathesis cyclooligomerization and their host guest binding study
    Organic Letters, 2016
    Co-Authors: Hai Long, Yinghua Jin, Wei Zhang
    Abstract:

    Cyclic porphyrin trimers were synthesized through one-step cyclooligomerization via Alkyne Metathesis from diyne monomers. These macrocycles show interesting host–guest binding interactions with fullerenes, selectively binding C70 (6 × 103 M–1) over C60 and C84 (no binding observed). The fullerene-encapsulated host–guest complex can undergo guest or host exchange in the presence of another guest (2,4,6-tri(4-pyridyl)-1,3,5-triazine) or host (cage COP5) molecule with higher binding affinity.

  • dynamic covalent synthesis of aryleneethynylene cages through Alkyne Metathesis dimer tetramer or interlocked complex
    Chemical Science, 2016
    Co-Authors: Qi Wang, Yinghua Jin, Chenxi Zhang, Hai Long, Setareh Azarnoush, Wei Zhang
    Abstract:

    A dynamic covalent approach towards rigid aryleneethynylene covalent organic polyhedrons (COPs) was explored. Our study on the relationship of the COP structures and the geometry of their building blocks reveals that the topology of aryleneethynylene COPs strongly depends on the size of the building blocks. A tetramer (D2h symmetric), dimer, or interlocked complex can be formed from monomers with the same face-to-edge angle but in different sizes. As Alkyne Metathesis is a self-exchange reaction and non-directional, the cyclooligomerization of multi-Alkyne monomers involves both intramolecular cyclization and intermolecular Metathesis reaction, resulting in complicated thermodynamic process disturbed by kinetic competition. Although a tetrahedron-shaped tetramer (Td symmetric) has comparable thermodynamic stability to a D2h symmetric tetramer, its formation is kinetically disfavored and was not observed experimentally. Aryleneethynylene COPs consist of purely unsaturated carbon backbones and exhibit large internal cavities, which would have interesting applications in host–guest chemistry and development of porous materials.

  • solution phase dynamic assembly of permanently interlocked aryleneethynylene cages through Alkyne Metathesis
    Angewandte Chemie, 2015
    Co-Authors: Qi Wang, Yinghua Jin, Hai Long, Wei Zhang
    Abstract:

    Highly stable permanently interlocked aryleneethynylene molecular cages were synthesized from simple triyne monomers using dynamic Alkyne Metathesis. The interlocked complexes are predominantly formed in the reaction solution in the absence of any recognition motif and were isolated in a pure form using column chromatography. This study is the first example of the thermodynamically controlled solution-phase synthesis of interlocked organic cages with high stability.

Jeffrey S. Moore - One of the best experts on this subject based on the ideXlab platform.

  • Product Distribution from Precursor Bite Angle Variation in Multitopic Alkyne Metathesis: Evidence for a Putative Kinetic Bottleneck
    Journal of the American Chemical Society, 2018
    Co-Authors: Timothy P. Moneypenny, Anna Yang, Nathan P. Walter, Toby J. Woods, Danielle L. Gray, Yang Zhang, Jeffrey S. Moore
    Abstract:

    In the dynamic synthesis of covalent organic frameworks and molecular cages, the typical synthetic approach involves heuristic methods of discovery. While this approach has yielded many remarkable products, the ability to predict the structural outcome of subjecting a multitopic precursor to dynamic covalent chemistry (DCC) remains a challenge in the field. The synthesis of covalent organic cages is a prime example of this phenomenon, where precursors designed with the intention of affording a specific product may deviate dramatically when the DCC synthesis is attempted. As such, rational design principles are needed to accelerate discovery in cage synthesis using DCC. Herein, we test the hypothesis that precursor bite angle contributes significantly to the energy landscape and product distribution in multitopic Alkyne Metathesis (AM). By subjecting a series of precursors with varying bite angles to AM, we experimentally demonstrate that the product distribution, and convergence toward product formation, ...

  • synthesis of cycloparaphenyleneacetylene via Alkyne Metathesis c70 complexation and copper free triple click reaction
    Journal of the American Chemical Society, 2016
    Co-Authors: Semin Lee, Danielle L. Gray, Etienne Chenard, Jeffrey S. Moore
    Abstract:

    Alkyne Metathesis provided an efficient macrocyclization route to a cycloparaphenyleneacetylene derivative in high yield. The cavity size was suitably matched for C70 which was tightly bound in an induced-fit fashion. The strained Alkynes enabled a copper-free, 3-fold azide–Alkyne cycloaddition at 50 °C.

  • kinetically trapped tetrahedral cages via Alkyne Metathesis
    Journal of the American Chemical Society, 2016
    Co-Authors: Semin Lee, Anna Yang, Timothy P. Moneypenny, Jeffrey S. Moore
    Abstract:

    In dynamic covalent synthesis, kinetic traps are perceived as disadvantageous, hindering the system from reaching its thermodynamic equilibrium. Here we present the near-quantitative preparation of tetrahedral cages from simple tritopic precursors using Alkyne Metathesis. While the cages are the presumed thermodynamic sink, we experimentally demonstrate that the products no longer exchange their vertices once they have formed. The example reported here illustrates that kinetically trapped products may facilitate high yields of complex products from dynamic covalent synthesis.

  • Synthesis of Cycloparaphenyleneacetylene via Alkyne Metathesis: C70 Complexation and Copper-Free Triple Click Reaction
    2016
    Co-Authors: Semin Lee, Danielle L. Gray, Etienne Chénard, Jeffrey S. Moore
    Abstract:

    Alkyne Metathesis provided an efficient macrocyclization route to a cyclo­parap­henylene­acetylene derivative in high yield. The cavity size was suitably matched for C70 which was tightly bound in an induced-fit fashion. The strained Alkynes enabled a copper-free, 3-fold azide–Alkyne cycloaddition at 50 °C

  • directional cyclooligomers via Alkyne Metathesis
    Journal of the American Chemical Society, 2012
    Co-Authors: Scott W Sisco, Jeffrey S. Moore
    Abstract:

    Macrocyclic oligomers possessing direction-defining ester linkages were synthesized via Metathesis of the nondirectional Alkyne functional group. Alkyne Metathesis is expected to scramble the relative orientation of adjacent ester groups, potentially leading to a complex mixture of macrocyclic products. We wondered whether a narrow product distribution would be achievable with a proper choice of the building block structure. Here we show that the shape of the building block determines whether the macrocyclic products are directionally uniform or scrambled. Specifically, two isomeric arylene-ethynylene polyesters afforded significantly different product distributions upon being subjected to depolymerization–macrocyclization. These results underscore the importance of learning how the shape and geometry of the building blocks affect the macrocyclization energy landscape.

Semin Lee - One of the best experts on this subject based on the ideXlab platform.

  • impact of ligands and metals on the formation of metallacyclic intermediates and a nontraditional mechanism for group vi Alkyne Metathesis catalysts
    Journal of the American Chemical Society, 2021
    Co-Authors: Richard R Thompson, Madeline E Rotella, Xin Zhou, Frank R Fronczek, Osvaldo Gutierrez, Semin Lee
    Abstract:

    The intermediacy of metallacyclobutadienes as part of a [2 + 2]/retro-[2 + 2] cycloaddition-based mechanism is a well-established paradigm in Alkyne Metathesis with alternative species viewed as off-cycle decomposition products that interfere with efficient product formation. Recent work has shown that the exclusive intermediate isolated from a siloxide podand-supported molybdenum-based catalyst was not the expected metallacyclobutadiene but instead a dynamic metallatetrahedrane. Despite their paucity in the chemical literature, theoretical work has shown these species to be thermodynamically more stable as well as having modest barriers for cycloaddition. Consequentially, we report the synthesis of a library of group VI alkylidynes as well as the roles metal identity, ligand flexibility, secondary coordination sphere, and substrate identity all have on isolable intermediates. Furthermore, we report the disparities in catalyst competency as a function of ligand sterics and metal choice. Dispersion-corrected DFT calculations are used to shed light on the mechanism and role of ligand and metal on the intermediacy of metallacyclobutadiene and metallatetrahedrane as well as their implications to Alkyne Metathesis.

  • siloxide podand ligand as a scaffold for molybdenum catalyzed Alkyne Metathesis and isolation of a dynamic metallatetrahedrane intermediate
    Organometallics, 2019
    Co-Authors: Richard R Thompson, Madeline E Rotella, Xin Zhou, Frank R Fronczek, Osvaldo Gutierrez, Revati Kumar, Semin Lee
    Abstract:

    Triphenylsiloxide is one of the most successful ancillary ligands for Mo(VI)-Alkyne Metathesis catalysts. It was proposed that flexible siloxide ligands allow Mo–O–Si bond angles to modulate the electrophilicity of Mo≡C and thereby promote the catalysis. Introduction of a siloxide podand ligand allowed elucidation of the effect of ligand flexibility and Mo–O–Si angles on the electrophilicity of Mo≡C. It also allowed for the isolation of a rare metallatetrahedrane of Mo(VI) which was found to be dynamic in solution.

  • synthesis of cycloparaphenyleneacetylene via Alkyne Metathesis c70 complexation and copper free triple click reaction
    Journal of the American Chemical Society, 2016
    Co-Authors: Semin Lee, Danielle L. Gray, Etienne Chenard, Jeffrey S. Moore
    Abstract:

    Alkyne Metathesis provided an efficient macrocyclization route to a cycloparaphenyleneacetylene derivative in high yield. The cavity size was suitably matched for C70 which was tightly bound in an induced-fit fashion. The strained Alkynes enabled a copper-free, 3-fold azide–Alkyne cycloaddition at 50 °C.

  • kinetically trapped tetrahedral cages via Alkyne Metathesis
    Journal of the American Chemical Society, 2016
    Co-Authors: Semin Lee, Anna Yang, Timothy P. Moneypenny, Jeffrey S. Moore
    Abstract:

    In dynamic covalent synthesis, kinetic traps are perceived as disadvantageous, hindering the system from reaching its thermodynamic equilibrium. Here we present the near-quantitative preparation of tetrahedral cages from simple tritopic precursors using Alkyne Metathesis. While the cages are the presumed thermodynamic sink, we experimentally demonstrate that the products no longer exchange their vertices once they have formed. The example reported here illustrates that kinetically trapped products may facilitate high yields of complex products from dynamic covalent synthesis.

  • Synthesis of Cycloparaphenyleneacetylene via Alkyne Metathesis: C70 Complexation and Copper-Free Triple Click Reaction
    2016
    Co-Authors: Semin Lee, Danielle L. Gray, Etienne Chénard, Jeffrey S. Moore
    Abstract:

    Alkyne Metathesis provided an efficient macrocyclization route to a cyclo­parap­henylene­acetylene derivative in high yield. The cavity size was suitably matched for C70 which was tightly bound in an induced-fit fashion. The strained Alkynes enabled a copper-free, 3-fold azide–Alkyne cycloaddition at 50 °C

Felix R Fischer - One of the best experts on this subject based on the ideXlab platform.

  • templated synthesis of end functionalized graphene nanoribbons through living ring opening Alkyne Metathesis polymerization
    Journal of the American Chemical Society, 2019
    Co-Authors: Stephen Von Kugelgen, Felix R Fischer, Ilya Piskun, James H Griffin, Christopher T Eckdahl, Nanette N Jarenwattananon
    Abstract:

    Atomically precise bottom-up synthesized graphene nanoribbons (GNRs) are promising candidates for next-generation electronic materials. The incorporation of these highly tunable semiconductors into complex device architectures requires the development of synthetic tools that provide control over the absolute length, the sequence, and the end groups of GNRs. Here, we report the living chain-growth synthesis of chevron-type GNRs (cGNRs) templated by a poly-(arylene ethynylene) precursor prepared through ring-opening Alkyne Metathesis polymerization (ROAMP). The strained triple bonds of a macrocyclic monomer serve both as the site of polymerization and the reaction center for an annulation reaction that laterally extends the conjugated backbone to give cGNRs with predetermined lengths and end groups. The structural control provided by a living polymer-templated synthesis of GNRs paves the way for their future integration into hierarchical assemblies, sequence-defined heterojunctions, and well-defined single-GNR transistors via block copolymer templates.

  • regioselective termination reagents for ring opening Alkyne Metathesis polymerization
    Journal of the American Chemical Society, 2017
    Co-Authors: Hyangsoo Jeong, Felix R Fischer, Stephen Von Kugelgen, Donatela E Bellone
    Abstract:

    Alkyne cross-Metathesis of molybdenum carbyne complex [TolC≡Mo(OCCH3(CF3)2)3]·DME with 2 equiv of functional ynamines or ynamides yields the primary cross-Metathesis product with high regioselectivity (>98%) along with a molybdenum metallacyclobutadiene complex. NMR and X-ray crystal structure analysis reveals that ynamides derived from 1-(phenylethynyl)pyrrolidin-2-one selectively cleave the propagating molybdenum species in the ring-opening Alkyne Metathesis polymerization (ROAMP) of ring-strained 3,8-dihexyloxy-5,6-dihydro-11,12-didehydrodibenzo[a,e][8]annulene and irreversibly deactivate the diamagnetic molybdenum metallacyclobutadiene complex through a multidentate chelate binding mode. The chain termination of living ROAMP with substituted ethynylpyrrolidin-2-ones selectively transfers a functional end-group to the polymer chain, giving access to telechelic polymers. This regioselective carbyne transfer strategy gives access to amphiphilic block copolymers through synthetic cascades of ROAMP followe...

  • regioselective carbyne transfer to ring opening Alkyne Metathesis initiators gives access to telechelic polymers
    Journal of the American Chemical Society, 2017
    Co-Authors: Stephen Von Kugelgen, Felix R Fischer, Renee J Sifri, Donatela E Bellone
    Abstract:

    Regioselective carbyne-transfer reagents derived from (3,3,3-trifluoroprop-1-yn-1-yl)benzene give access to functionalized ring-opening Alkyne Metathesis polymerization (ROAMP) initiators [R-C6H4C≡Mo(OC(CH3)(CF3)2)3] featuring electron-donating or -withdrawing substituents on the benzylidyne. Kinetic studies and linear free-energy relationships reveal that the initiation step of the ring-opening Alkyne Metathesis polymerization of 5,6,11,12-tetradehydrobenzo[a,e][8]annulene exhibits a moderate positive Hammett reaction constant (ρ = +0.36). ROAMP catalysts featuring electron-withdrawing benzylidynes not only selectively increase the rate of initiation (ki) over the rate of propagation (kp) but also prevent undesired intra- and intermolecular chain-transfer processes, giving access to linear poly-(o-phenylene ethynylene) with narrow molecular weight distribution. The regioselective carbyne transfer methodology and the detailed mechanistic insight enabled the design of a bifunctional ROAMP-reversible additi...

  • initiator control of conjugated polymer topology in ring opening Alkyne Metathesis polymerization
    Journal of the American Chemical Society, 2016
    Co-Authors: Stephen Von Kugelgen, Felix R Fischer, Donatela E Bellone, Ryan R Cloke, Wade S Perkins
    Abstract:

    Molybdenum carbyne complexes [RC≡Mo(OC(CH3)(CF3)2)3] featuring a mesityl (R = Mes) or an ethyl (R = Et) substituent initiate the living ring-opening Alkyne Metathesis polymerization of the strained cyclic Alkyne, 5,6,11,12-tetradehydrobenzo[a,e][8]annulene, to yield fully conjugated poly(o-phenylene ethynylene). The difference in the steric demand of the polymer end-group (Mes vs Et) transferred during the initiation step determines the topology of the resulting polymer chain. While [MesC≡Mo(OC(CH3)(CF3)2)3] exclusively yields linear poly(o-phenylene ethynylene), polymerization initiated by [EtC≡Mo(OC(CH3)(CF3)2)3] results in cyclic polymers ranging in size from n = 5 to 20 monomer units. Kinetic studies reveal that the propagating species emerging from [EtC≡Mo(OC(CH3)(CF3)2)3] undergoes a highly selective intramolecular backbiting into the butynyl end-group.

  • alcohol promoted ring opening Alkyne Metathesis polymerization
    Angewandte Chemie, 2013
    Co-Authors: Daniel W Paley, Michael L Steigerwald, Danielle F Sedbrook, John Decatur, Felix R Fischer, Colin Nuckolls
    Abstract:

    Alcohol is the answer! An inactive, air-stable, dimeric molybdenum alkylidyne complex is activated toward ring-opening Alkyne Metathesis polymerization (ROAMP) by the addition of methanol. The ROAMP is compatible with water and phenol-containing substrates and with the in situ photochemical generation of Alkyne monomers from cyclopropenones.