Transition metal alkylidene complexes. Pathways in their formation and tautomerization between bis-alkylidenes and alkyl alkylidynes

Chen, Xue-Tai; Morton, Laurel A.

doi:10.1016/j.jorganchem.2011.06.048

Cited by 20 publications

(12 citation statements)

References 89 publications

(108 reference statements)

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“…At this temperature, the broad signal of the corresponding carbene is split. This suggests that both syn and anti isomers exist (Supporting Information, Scheme S2), indicative of the rigid behavior of the two carbenes ,. Furthermore, the proton signal at 2 ppm (previously assigned to the ≡Si−NH 2 group coordinated to W) is more intense at 340 K, supporting the effect of coordination between N and W atoms at high temperatures.…”

Section: Methodsmentioning

confidence: 74%

Tungsten(VI) Carbyne/Bis(carbene) Tautomerization Enabled by N‐Donor SBA15 Surface Ligands: A Solid‐State NMR and DFT Study

et al. 2016

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Designing supported well-defined bis(carbene) complexes remains akey challenge in heterogeneous catalysis. The reaction of W(CtBu)(CH 2 tBu) 3 with amine-modified mesoporous SBA15 silica, which has vicinal silanol/silylamine pairs [( SiOH)( SiNH 2 )],l eads to [( SiNH 2 À )( SiO À )W( CHtBu)(CH 2 tBu) 2 ]a nd [( SiNH 2 À )( SiO À )W( = CHtBu) 2 -(CH 2 tBu). Variable temperature, 1 H-1 H2 Dd ouble-quantum, 1 H-13 CH ETCOR, and HETCOR with spin diffusion solidstate NMR spectroscopydemonstrate tautomerization between the alkyla lkylidyne and the bis(alkylidene) on the SBA15 surface.Suchequilibrium is possible through the coordination of Wt ot he surface [( Si À OH)( Si À NH 2 )] groups,w hich act as a[ N,O] pincer ligand. DFT calculations provide ar ationalization for the surface-complex tautomerization and support the experimental results.T his direct observation of such ap rocess shows the strong similarity between molecular mechanisms in homogeneous and heterogeneous catalysis.I n propane metathesis (at 150 8 8C), the tungsten bis(carbene) tautomer is favorable,w ith at urnover number (TON) of 262. It is the highest TONa mong all the tungsten alkyl-supported catalysts.

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Section: Methodsmentioning

confidence: 74%

Tungsten(VI) Carbyne/Bis(carbene) Tautomerization Enabled by N‐Donor SBA15 Surface Ligands: A Solid‐State NMR and DFT Study

et al. 2016

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“…Next, the well-established α-hydrogen transfer from the alkyl to alkylidyne forms the W-carbene. [22][23][24] A [2 + 2] cycloaddition followed by the cycloreversion leads to the internal alkene and the W-bis-carbene. Successive insertion/elimination steps (by chain walking) give the terminal alkene, which reacts to a new W-alkylidene.…”

Section: Resultsmentioning

confidence: 99%

Striking difference between alkane and olefin metathesis using the well-defined precursor [Si–O–WMe₅]: indirect evidence in favour of a bifunctional catalyst W alkylidene–hydride

Riache

Callens

Espinas

et al. 2015

Catal. Sci. Technol.

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“…The aim here is to summarize our understanding as to what are the major pathways of forming high-oxidation-state alkylidene complexes in both homogeneous and heterogeneous catalysts, as far as is known at this point, including systems in which only olefins are present. For detailed mechanistic and kinetic studies of the formation of alkylidenes, alkylidynes, and bis-alkylidene complexes in tantalum and tungsten chemistry, the reader is referred to work by Xue …”

Section: Introductionmentioning

confidence: 99%

Formation of High-Oxidation-State Metal–Carbon Double Bonds

Schrock

Copéret

2017

Organometallics

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This tutorial explores the major pathways of forming metal–carbon double bonds in high-oxidation-state alkylidene complexes that began with the alkylidene chemistry of tantalum complexes in the 1970s and continued with the organometallic chemistry of Mo, W, and Re and the development of homogeneous catalysts for the metathesis of olefins. It also explores recent findings in surface organometallic chemistry and discusses the link between molecularly defined and heterogeneous catalysts. Recent results suggest that heterogeneous olefin metathesis catalysts that are activated toward metathesis upon exposure to olefins produce a d0 alkylidene through formation of a metallacyclopentane ring at d2 metal sites followed by “a ring contraction” to a metallacyclobutane, a reaction that was first observed in tantalum chemistry.

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Transition metal alkylidene complexes. Pathways in their formation and tautomerization between bis-alkylidenes and alkyl alkylidynes

Cited by 20 publications

References 89 publications

Tungsten(VI) Carbyne/Bis(carbene) Tautomerization Enabled by N‐Donor SBA15 Surface Ligands: A Solid‐State NMR and DFT Study

Tungsten(VI) Carbyne/Bis(carbene) Tautomerization Enabled by N‐Donor SBA15 Surface Ligands: A Solid‐State NMR and DFT Study

Striking difference between alkane and olefin metathesis using the well-defined precursor [Si–O–WMe₅]: indirect evidence in favour of a bifunctional catalyst W alkylidene–hydride

Formation of High-Oxidation-State Metal–Carbon Double Bonds

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Transition metal alkylidene complexes. Pathways in their formation and tautomerization between bis-alkylidenes and alkyl alkylidynes

Cited by 20 publications

References 89 publications

Tungsten(VI) Carbyne/Bis(carbene) Tautomerization Enabled by N‐Donor SBA15 Surface Ligands: A Solid‐State NMR and DFT Study

Tungsten(VI) Carbyne/Bis(carbene) Tautomerization Enabled by N‐Donor SBA15 Surface Ligands: A Solid‐State NMR and DFT Study

Striking difference between alkane and olefin metathesis using the well-defined precursor [Si–O–WMe5]: indirect evidence in favour of a bifunctional catalyst W alkylidene–hydride

Formation of High-Oxidation-State Metal–Carbon Double Bonds

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Striking difference between alkane and olefin metathesis using the well-defined precursor [Si–O–WMe₅]: indirect evidence in favour of a bifunctional catalyst W alkylidene–hydride