Competitive isomerization and catalyst decomposition during ring-closing metathesis

Killeen, Charles; Liu, Jie; Zijlstra, Harmen S.; Maass, Florian; Piers, James; Adams, Reid B.; Oliver, Allen G.; McIndoe, J. Scott

doi:10.1039/d3cy00065f

Cited by 2 publications

(1 citation statement)

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“…ESI-MS is not helpful and only shows the [Fe(salen)] + or [Fe(salan)] + molecular ion. We therefore turned our attention to mass spectrometry to identify catalyst speciation and possible deactivation pathways. − For this purpose we employed LIFDI-MS, which is the softest ionization for mass spectrometry and has been used to detect highly sensitive and otherwise elusive organometallic species. , …”

Section: Resultsmentioning

confidence: 99%

The Complex Reactivity of [(salen)Fe]₂(μ-O) with HBpin and Its Implications in Catalysis

Hood,

Lau,

Diefenbach

et al. 2023

ACS Catal.

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We report a detailed study into the method of precatalyst activation during alkyne cyclotrimerization. During these studies we have prepared a homologous series of Fe(III)-μoxo(salen) complexes and use a range of techniques including UV−vis, reaction monitoring studies, single crystal X-ray diffraction, NMR spectroscopy, and LIFDI mass spectrometry to provide experimental evidence for the nature of the on-cycle iron catalyst. These data infer the likelihood of ligand reduction, generating an iron(salan)-boryl complex as a key on-cycle intermediate. We use DFT studies to interrogate spin states, connecting this to experimentally identified diamagnetic and paramagnetic species. The extreme conformational flexibility of the salan system appears connected to challenges associated with crystallization of likely on-cycle species.

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Section: Resultsmentioning

confidence: 99%

The Complex Reactivity of [(salen)Fe]₂(μ-O) with HBpin and Its Implications in Catalysis

Hood,

Lau,

Diefenbach

et al. 2023

ACS Catal.

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Protonation Effects on the Benzoxazine Formation Pathways and Products Distribution

Ribeiro,

Omari,

Scott McIndoe

et al. 2024

ChemPhysChem

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The effect of acidic media on the formation of the 3,4‐dihydro‐2H‐3‐phenyl‐1,3‐benzoxazine Bz is evaluated, focusing on the differentiation of intermediates and products formed by the distinct pathways observed in the presence and absence of acid. The use of real‐time mass spectrometry (PSI‐ESI‐MS) coupled to tandem MS and infrared multiple photon dissociation (IRMPD) allowed the differentiation of the species observed during the synthesis of benzoxazines in these different conditions. The results suggest that formic acid promotes the formation of aniline and phenol condensation products (IC and IIC) by protecting the aniline amino group and enhancing the formaldehyde electrophilicity. The results also suggest that although the presence of acid allow a more efficient potential energy landscape to be accessed, the last cyclization step for the formation of benzoxazines cannot be mediated by the protonation route intermediate (ROP Bz). Overall, the conclusions presented here provide important information about the synthesis of benzoxazines under acidic conditions, allowing the development of optimal reaction conditions.

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Competitive isomerization and catalyst decomposition during ring-closing metathesis

Abstract: Ring-closing metathesis (RCM) is an elegant means of forming cyclic structural elements in both simple and complex molecules. Mechanistically, the reaction cycle is well understood, though subtle details concerning the...

Cited by 2 publications

References 54 publications

The Complex Reactivity of [(salen)Fe]₂(μ-O) with HBpin and Its Implications in Catalysis

The Complex Reactivity of [(salen)Fe]₂(μ-O) with HBpin and Its Implications in Catalysis

Protonation Effects on the Benzoxazine Formation Pathways and Products Distribution

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Competitive isomerization and catalyst decomposition during ring-closing metathesis

Abstract: Ring-closing metathesis (RCM) is an elegant means of forming cyclic structural elements in both simple and complex molecules. Mechanistically, the reaction cycle is well understood, though subtle details concerning the...

Cited by 2 publications

References 54 publications

The Complex Reactivity of [(salen)Fe]2(μ-O) with HBpin and Its Implications in Catalysis

The Complex Reactivity of [(salen)Fe]2(μ-O) with HBpin and Its Implications in Catalysis

Protonation Effects on the Benzoxazine Formation Pathways and Products Distribution

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Product

Resources

About

The Complex Reactivity of [(salen)Fe]₂(μ-O) with HBpin and Its Implications in Catalysis

The Complex Reactivity of [(salen)Fe]₂(μ-O) with HBpin and Its Implications in Catalysis