Direct observation of reaction intermediates for a well defined heterogeneous alkene metathesis catalyst

Blanc, Frédéric; Berthoud, Romain; Copéret, Christophe; Lesage, Anne; Emsley, Lyndon; Singh, Rojendra; Kreickmann, Thorsten; Schrock, Richard R.

doi:10.1073/pnas.0802147105

Cited by 89 publications

(92 citation statements)

References 48 publications

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“…9,27,28 In contrast to all of the supported tungsten neopentylidene metathesis catalysts investigated so far, no mono-13 C-labeled 3,3-dimethylpropene was released when 2@SiO 2 was contacted with 15 equiv of bis( 13 Clabeled) ethylene, and the solid-state NMR of the catalyst after exposure was identical with that of the parent compound. It is noteworthy that no signals from methylidene and/or metallacyclobutane species were observable.…”

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Strongly σ Donating Thiophenoxide in Silica-Supported Tungsten Oxo Catalysts for Improved 1-Alkene Metathesis Efficiency

2015

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We report the synthesis of tungsten oxo alkylidene complexes bearing bulky thiophenoxide ligands [W(O)(CHtBu)-(SHMT) 2 (PMe 2 Ph)] and [W(O)(CHtBu)(SHMT) 2 ] (SHMT = 2,6-dimesitylthiophenoxide) and their grafting on partially dehydroxylated silica, affording the supported complexes [(SiO)W(O)(CHtBu)-(SHMT)(PMe 2 Ph)] and [(SiO)W(O)(CHtBu)(SHMT)]. While the molecular precursors are not significantly active in the metathesis of alkenes, the grafted analogue without bound phosphine ligands displays activity comparable to that of its aryloxide analogue [(SiO)W(O)( CHtBu)(OHMT)] (OHMT = 2,6-dimesitylphenoxide). It is worth noting that [(SiO)W(O)(CHtBu)(SHMT)] showed unprecedented activity in the metathesis of 1-alkenes, probably because of the lower stability of metallacyclobutane intermediates.A dvances in alkene metathesis over the last 30 years have transformed the way organic molecules are prepared. 1−3 Of d 0 alkene metathesis catalysts, 4−7 supported tungsten oxo alkylidene complexes have recently emerged and been shown to have unprecedented activities and stabilities. 8,9 In particular, silica-supported tungsten oxo alkylidene bearing phenolate ligands catalyze the metathesis of internal olefins at loading as low as 50 ppm. However, they are surprisingly sluggish for 1-alkenes, because of the formation of very stable unsubstituted metallacycles generated by the ethylene byproduct. This reversible deactivation process could be circumvented by using a reactor setup, allowing for the continuous removal of ethylene.DFT calculations have shown that dissymmetry at the metal center (X ≠ Y) for d 0 Schrock-type catalysts of general formula (X)(Y)M(E)(CHR) (M = Mo, W, Re; E = O, NR, CR) not only decreases the energy barrier for coordination of the olefin substrate (the key step in metathesis) but also raises the energy of the metallacyclobutane intermediates. 10−14 In silica-supported phenolate tungsten oxo alkylidene complexes such as [(SiO)W(O)(CHtBu)(OHMT)] and [(SiO)W( O)(CHtBu)(dAdPO)] (OHMT = 2,6-dimesitylphenoxide, dAdPO = 2,6-diadamantyl-4-methylphenoxide), the σ donations of the phenoxide and the surface siloxide ligands are very similar. We thus reasoned that thiolate analogues 15 would be ideal targets, since they are isoelectronic with the corresponding phenolates 16−19 with the advantage of restoring the dissymmetry at the metal center.Herein we report the synthesis, the grafting on partially dehydroxylated silica at 700°C (SiO 2-(700) ), and the catalytic performance of oxo alkylidene complexes with pendant thiolate ligands [W(O)(CHtBu)(SHMT) 2 (PMe 2 Ph)] (1) and [W(O)(CHtBu)(SHMT) 2 ] (2) (SHMT = 2,6-dimesitylthiophenoxide) 15,20 and the corresponding supported systems.The thiolate complex 1 was synthesized by salt metathesis of [W(O)(CHtBu)Cl 2 (PMe 2 Ph) 2 ] 21,22 with 2 equiv of potassium 2,6-dimesitylthiophenolate in 70% yield. A similar synthesis was independently described by Schrock and Hoveyda during the course of our studies. 16 The phosphinefree complex 2 was prepare...

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Strongly σ Donating Thiophenoxide in Silica-Supported Tungsten Oxo Catalysts for Improved 1-Alkene Metathesis Efficiency

2015

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“…Key intermediates in catalytic metathesis reactions catalyzed by surface-attached species have only recently been observed in a study involving W(NAr)(CH- t -Bu)(2,5-Me 2 Pyr) 2 that has been grafted onto SiO 2 (700) ciii. Addition of W(NAr)(CH- t -Bu)(2,5-Me 2 Pyr) 2 to SiO 2 (700) yields W(NAr)(CH- t -Bu)(2,5-Me 2 Pyr)(OSi 700 ) as the major species (∼90%) along with W(NAr)(CH 2 - t -Bu)(2,5-Me 2 Pyr) 2 (OSi 700 ), according to mass balance analysis, IR, and NMR studies.…”

Section: Catalysts Supported On Silicamentioning

confidence: 99%

Recent Advances in High Oxidation State Mo and W Imido Alkylidene Chemistry

2009

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Introduction 3211 2. Principles of Tungsten and Molybdenum Imido Alkylidene Chemistry 3212 3. Precursors to Bisalkoxides and Monoalkoxides 3214 4. Studies Concerning Monoalkoxide Pyrrolide (MAP) Species 3216 5. Catalyst Decomposition in Solution 3218 6. Regeneration of Alkylidenes 3220 7. Catalysts Supported on Silica 3221 8. New Reactions 3222 9. Concluding Remarks 3224 10. Acknowledgments 3224 11. References 3224

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“…6a) [74] and silica-supported tungsten [75][76][77][78] and molybdenum complexes (Fig. 6b) [79][80][81][82] are effective catalysts for alkane metathesis [69,71,77,[83][84][85].…”

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confidence: 99%

Supported Single-Site Organometallic Catalysts for the Synthesis of High-Performance Polyolefins

2014

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Single-site organometallic catalysts supported on solid inorganic or organic substrates are making an important contribution to heterogeneous catalysis. Early and late transition metal single-site catalysts have changed the polyolefin manufacturing industry and research with their ability to produce polymers with unique properties. Moreover, several of these catalysts have been commercialized on a large scale. Their heterogenization for slurry or gas phase olefin polymerization is important to produce polyolefin as beads and to avoid reactor fouling. The large majority of supports currently used in industry are inorganic materials (SiO 2 , Al 2 O 3 , MgCl 2 ), with silica being the most important. Single-site supported catalysts are most commonly prepared by molecular-level anchoring/chemisorption, in which a molecular precursor undergoes reaction with the surface while maintaining most of the ligand sphere of the parent molecule. Chemisorption of discrete organometallic complexes on solid supports yields catalysts with well-defined active sites, greater thermal stability than the homogeneous analogues, and decreased reactor fouling versus the homogeneous analogues. This review presents a detailed account of the synthesis, characterization and polymerization properties of single-site catalysts supported on metal oxides and metal sulfated oxides, primarily carried out at Northwestern University.

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Direct observation of reaction intermediates for a well defined heterogeneous alkene metathesis catalyst

Cited by 89 publications

References 48 publications

Strongly σ Donating Thiophenoxide in Silica-Supported Tungsten Oxo Catalysts for Improved 1-Alkene Metathesis Efficiency

Strongly σ Donating Thiophenoxide in Silica-Supported Tungsten Oxo Catalysts for Improved 1-Alkene Metathesis Efficiency

Recent Advances in High Oxidation State Mo and W Imido Alkylidene Chemistry

Supported Single-Site Organometallic Catalysts for the Synthesis of High-Performance Polyolefins

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