Well‐Defined Models for the Elusive Dinuclear Intermediates of the Pauson–Khand Reaction

Hartline, Douglas R.; Zeller, Mat­thias; Uyeda, Christopher

doi:10.1002/anie.201601784

Cited by 23 publications

(22 citation statements)

References 38 publications

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“…The successful isolation of the η 2 ‐alkene‐µ‐alkyne‐Co 2 (CO) 5 complexes 2 that represent the first fully characterized examples of the initial phase of the Pauson–Khand reaction,, prompted us to investigate a potentially more flexible system that could yield either an intramolecular product, or possibly another intermediate in the PKR pathway . As noted above, 6 H ‐dibenzo[ a , e ]cyclooctatrien‐5‐one ( 6 , Figure ) was converted into the alkynyl‐Co 2 (CO) 6 complexes 8 (Figure and Figure ).…”

Section: Resultsmentioning

confidence: 99%

Alkynyldicobalt Derivatives of Dibenzosuberenol and Dibenzocyclooctatrien‐5‐ol: Ring Conformations, Ease of Carbonyl Elimination and Relevance to Pauson–Khand Cyclization

et al. 2017

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Under very mild conditions, (5-alkynyl-5H-dibenzo-[a,d]cycloheptatrien-5-ol)Co 2 (CO) 6 clusters 1 lose a carbon monoxide ligand and form the corresponding η 2 -alkene-μ-alkyne-Co 2 (CO) 5 complexes 2 (the first isolated examples of the initial phase of the Pauson-Khand reaction). This behaviour is not paralleled by the homologue in which an additional methylene group has been inserted within the seven-membered ring, as in the [5-alkynyl-6H-dibenzo[a,e]cyclooctatrienol]Co 2 -(CO) 6 system 8, for which several X-ray crystal structures are reported. The apparent additional flexibility of this molecular framework does not translate into conformations appropriate for the formation of η 2 -alkene-μ-alkyne-Co 2 (CO) 5 complexes. The relative inertness of the ethynyl complex 1a, compared [a] 2051 ing of the seven-membered ring towards the cluster, such that this distance, d, shortens to 2.04 Å. In contrast, in the eightmembered ring complex 8a, not only is the corresponding bond-centroid-to-cobalt distance, d, considerably longer (ca. 4.2 Å), but the C11=C12 double bond is also twisted away from the horizontal, as depicted in Figure 6b.

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Section: Resultsmentioning

confidence: 99%

Alkynyldicobalt Derivatives of Dibenzosuberenol and Dibenzocyclooctatrien‐5‐ol: Ring Conformations, Ease of Carbonyl Elimination and Relevance to Pauson–Khand Cyclization

et al. 2017

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“…The Ni 2 (C 6 H 6 )-(NDI) complex is a versatile catalyst precursor for a wide variety of transformations, including hydrosilylation, 78 alkyne trimerization, 79 and nitrene dimerization. 80 This dinickel system was also used to model several proposed steps in a Pauson−Khand reaction, such that a bound alkyne complex and a nickelacyclic product of oxidative cyclization (Scheme 7) were observed, 81 accomplishing a long-standing goal in organometallic chemistry. 82 Additionally, treatment of the nickelacycle with CO generated the desired cyclopentenone product in high yield.…”

Section: ■ Unsymmetrical Ligandsmentioning

confidence: 99%

Bimetallics in a Nutshell: Complexes Supported by Chelating Naphthyridine-Based Ligands

et al. 2020

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Conspectus: Bimetallic motifs are a structural feature common to some of the most effective and synthetically useful catalysts known, including in the active sites of many metalloenzymes and on the surfaces of industrially relevant heterogeneous materials. However, the complexity of these systems often hampers detailed studies of their fundamental properties. To glean valuable mechanistic insight into how these catalysts function, this research group has prepared a family of dinucleating 1,8-naphthyridine ligands that bind two first-row transition metals in close proximity, originally designed to help mimic the proposed active site of metal oxide surfaces. Of the various bimetallic combinations examined, dicopper(I) is particularly versatile, as neutral bridging ligands adopt a variety of different binding modes depending on the configuration of frontier orbitals available to interact with the Cu centers. Organodicopper complexes are readily accessible, either through the traditional route of salt metathesis or via the activation of tetraarylborate anions through aryl group abstraction by a dicopper(I) unit. The resulting bridging aryl complexes engage in C-H bond activations, notably with terminal alkynes to afford bridging alkynyl species. The µhydrocarbyl complexes are surprisingly tolerant of water and elevated temperatures. This stability was leveraged to isolate a species that typically represents a fleeting intermediate in Cu-catalyzed azide-alkyne coupling (CuAAC); reaction of a bridging alkynyl complex with an organic azide afforded the first example of a well-defined, symmetrically bridged dicopper triazolide. This complex was shown to be an intermediate during CuAAC, providing support for a proposed bimetallic mechanism. These platforms are not limited to formally low oxidation states; chemical oxidation of the hydrocarbyl complexes cleanly results in formation of mixed-valent Cu I Cu II complexes with varying degrees of distortion in both the bridging moiety and the dicopper core. Higher oxidation states, i.e. dicopper(II), are easily accessed via oxidation of a dicopper(I) compound with air to give a Cu II 2(µ-OH)2 complex. Reduction of this compound with silanes resulted in the unexpected formation of pentametallic copper(I) dihydride clusters or trimetallic monohydride complexes, depending on the nature of the silane. Finally, development of an unsymmetrical naphthyridine ligand with mixed donor side-arms enables selective synthesis of an isostructural series of six heterobimetallic complexes, demonstrating the power of ligand design in the preparation of heterometallic assemblies.

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“…In our previous studies, we identified alkynes as strongly coordinating ligands that could potentially displace norbornadiene following C–C reductive elimination (Figure a). Accordingly, addition of 1-phenylpropyne to solutions of 3 resulted in the release of free norbornadiene and the formation of the previously characterized [ i ‑Pr NDI]Ni 2 (PhCCMe) complex 4 . With an equimolar stoichiometry of 1-phenylpropyne and 3 , the reaction does not reach full conversion but establishes a stable equilibrium after approximately 5 min ( K eq = 2.1).…”

Section: Strain-driven Dinuclear C–c Oxidative Additionmentioning

confidence: 97%

Catalytic Carbonylative Rearrangement of Norbornadiene via Dinuclear Carbon–Carbon Oxidative Addition

2017

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Single bonds between carbon atoms are inherently challenging to activate using transition metals; however, ring-strain release can provide the necessary thermodynamic driving force to make such processes favorable. In this report, we describe a strain-induced C-C oxidative addition of norbornadiene. The reaction is mediated by a dinuclear Ni complex, which also serves as a catalyst for the carbonylative rearrangement of norbornadiene to form a bicyclo[3.3.0] product.

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Well‐Defined Models for the Elusive Dinuclear Intermediates of the Pauson–Khand Reaction

Cited by 23 publications

References 38 publications

Alkynyldicobalt Derivatives of Dibenzosuberenol and Dibenzocyclooctatrien‐5‐ol: Ring Conformations, Ease of Carbonyl Elimination and Relevance to Pauson–Khand Cyclization

Alkynyldicobalt Derivatives of Dibenzosuberenol and Dibenzocyclooctatrien‐5‐ol: Ring Conformations, Ease of Carbonyl Elimination and Relevance to Pauson–Khand Cyclization

Bimetallics in a Nutshell: Complexes Supported by Chelating Naphthyridine-Based Ligands

Catalytic Carbonylative Rearrangement of Norbornadiene via Dinuclear Carbon–Carbon Oxidative Addition

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