Synthesis and dynamic behaviour of a dimeric ruthenium benzylidene complex bearing a truncated N-heterocyclic carbene ligand

Higman, Carolyn S.; Rufh, Stephanie A.; McDonald, Robert; Fogg, Deryn E.

doi:10.1016/j.jorganchem.2017.03.033

Cited by 5 publications

(3 citation statements)

References 53 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…This confirms the detrimental effects of ethylene. However, not even careful removal of ethylene during metathesis and low catalyst loading to minimize decomposition via dinuclear ruthenium complexes 14,30,31 are enough to stop catalyst decomposition. 32 When searching for alternative culprits, the fact that decomposition products generated in the absence of an olefinic substrate are not isomerization-active enough 18 should be guiding.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

Loss and Reformation of Ruthenium Alkylidene: Connecting Olefin Metathesis, Catalyst Deactivation, Regeneration, and Isomerization

et al. 2017

View full text Add to dashboard Cite

Ruthenium-based olefin metathesis catalysts are used in laboratory-scale organic synthesis across chemistry, largely thanks to their ease of handling and functional group tolerance. In spite of this robustness, these catalysts readily decompose, via little-understood pathways, to species that promote double-bond migration (isomerization) in both the 1-alkene reagents and the internal-alkene products. We have studied, using density functional theory (DFT), the reactivity of the Hoveyda-Grubbs second-generation catalyst 2 with allylbenzene, and discovered a facile new decomposition pathway. In this pathway, the alkylidene ligand is lost, via ring expansion of the metallacyclobutane intermediate, leading to the spin-triplet 12-electron complex (SIMes)RuCl (R21, SIMes = 1,3-bis(2,4,6-trimethylphenyl)-4,5-dihydroimidazol-2-ylidene). DFT calculations predict R21 to be a very active alkene isomerization initiator, either operating as a catalyst itself, via a η-allyl mechanism, or, after spin inversion to give R21 and formation of a cyclometalated Ru-hydride complex, via a hydride mechanism. The calculations also suggest that the alkylidene-free ruthenium complexes may regenerate alkylidene via dinuclear ruthenium activation of alkene. The predicted capacity to initiate isomerization is confirmed in catalytic tests using p-cymene-stabilized R21 (5), which promotes isomerization in particular under conditions favoring dissociation of p-cymene and disfavoring formation of aggregates of 5. The same qualitative trends in the relative metathesis and isomerization selectivities are observed in identical tests of 2, indicating that 5 and 2 share the same catalytic cycles for both metathesis and isomerization, consistent with the calculated reaction network covering metathesis, alkylidene loss, isomerization, and alkylidene regeneration.

show abstract

Section: ■ Results and Discussionmentioning

confidence: 99%

Loss and Reformation of Ruthenium Alkylidene: Connecting Olefin Metathesis, Catalyst Deactivation, Regeneration, and Isomerization

et al. 2017

View full text Add to dashboard Cite

show abstract

“…Another resonance appeared at δ P 34.9 ppm in the 31 P NMR spectrum of the reaction mixture of 1 (Figure ). This resonance was tentatively ascribed to possible dimerization, ,,− though other decomposition products cannot be excluded . The tentative assignment of the 31 P NMR resonances at δ P 24.3 and 34.9 ppm to the active catalytic species 1a and a possible dimeric species ( 1b ), respectively, is supported by the observation of a molecular ion with m / z 542, which may be ascribed to the molecular ions [M 1a ] + and/or [M 1b ] 2+ , by MALDI–TOF MS (Figure S8).…”

Section: Results and Discussionmentioning

confidence: 81%

Comparison of the Spectroscopically Measured Catalyst Transformation and Electrochemical Properties of Grubbs’ First- and Second-Generation Catalysts

2021

View full text Add to dashboard Cite

According to UV−vis spectroscopy (0.10 mM, CH 2 Cl 2 at 25 °C), the catalyst transformation (which could possibly include ligand dissociation with active catalyst formation, dimer formation, and decomposition) rate constants (k obs ) of Grubbs' first (1) and second (2) generation catalysts are 7.48 × 10 −5 and 1.52 × 10 −4 s −1 , respectively. From 31 P NMR (0.1 M, CD 2 Cl 2 , at 25 °C), the catalyst transformation was 5.1% for 1 and 16.5% for 2 after 72 h. However, due to the larger concentrations of the NMR samples compared to the UV−vis samples, the extent of transformation did not correspond. The oxidation potential of the Ru II /Ru III couple of 2 (E°' = 27.5 mV at v = 200 mV s −1 ) was considerably lower than that of 1 (E°' = 167 mV at v = 200 mV s −1 ). In the case of 1, a second reduction peak appeared at slow scan rates. This may probably be ascribed to an electrochemically active compound that was formed from the intermediate cation 1 •+ and the subsequent reduction of the latter. The oxidation/ reduction of 1 proceeds according to an E r C i electrochemical mechanism (E r = electrochemically reversible step, C i = chemically irreversible step), whereas 2 proceeds according to an E r C r electrochemical mechanism (E r = electrochemically reversible step, C i = chemically reversible step).

show abstract

“…Known Ru–IMe n complexes ,− include “mixed-NHC” indenylidene and benzylidene catalysts . However, access to RuCl 2 (IMe 4 )(PCy 3 )(CHPh) GII′ (the IMe 4 analogue of GII ) is hampered by facile formation of an unreactive dimer, the metathesis inactivity of which precludes access to the active species RuCl 2 (IMe 4 )(CH 2 ) Ru-1′ . As an alternative approach, we sought to effect ligand exchange of the resting-state Grubbs methylidene GIm with free IMe 4 .…”

mentioning

confidence: 99%

Rapid Decomposition of Olefin Metathesis Catalysts by a Truncated N-Heterocyclic Carbene: Efficient Catalyst Quenching and N-Heterocyclic Carbene Vinylation

et al. 2018

Self Cite

View full text Add to dashboard Cite

The Grubbs methylidene RuCl2(PCy3)2(CH2) GIm is immediately decomposed by the small N-heterocyclic carbene (NHC) tetramethylimidazol-2-ylidene (IMe4), even at −80 °C. Labeling experiments with RuCl2(PCy3)2(13CH2) reveal capture of the methylidene ligand as ethylimidazolium chloride [13CH3 13CH2–IMe4]Cl, A*. Density functional calculations indicate that IMe4 first abstracts methylidene from five-coordinate GIm (a pathway unavailable to bulkier NHCs), generating the N-heterocyclic olefin (NHO) H2CIMe4. The latter attacks a second GIm; protonolysis of highly basic [Ru]–CH2CH2IMe4 then liberates A. Identical, slightly slower, reactivity is seen for RuCl2(H2IMes)(PCy3)(CH2), GIIm. The high efficiency of this process opens up opportunities for tandem metathesis enabled by sterically accessible NHCs and NHOs.

show abstract

Synthesis and dynamic behaviour of a dimeric ruthenium benzylidene complex bearing a truncated N-heterocyclic carbene ligand

Cited by 5 publications

References 53 publications

Loss and Reformation of Ruthenium Alkylidene: Connecting Olefin Metathesis, Catalyst Deactivation, Regeneration, and Isomerization

Loss and Reformation of Ruthenium Alkylidene: Connecting Olefin Metathesis, Catalyst Deactivation, Regeneration, and Isomerization

Comparison of the Spectroscopically Measured Catalyst Transformation and Electrochemical Properties of Grubbs’ First- and Second-Generation Catalysts

Rapid Decomposition of Olefin Metathesis Catalysts by a Truncated N-Heterocyclic Carbene: Efficient Catalyst Quenching and N-Heterocyclic Carbene Vinylation

Contact Info

Product

Resources

About