Large-Scale Syntheses of Several Synthons to the Dearomatization Agent {TpW(NO)(PMe<sub>3</sub>)} and Convenient Spectroscopic Tools for Product Analysis

Welch, Kevin D.; Harrison, Daniel P.; Lis, Edward C.; Liu, Weijun; Salomon, A.; Harman, W. Dean; Myers, William H.

doi:10.1021/om070034g

Cited by 41 publications

(111 citation statements)

References 16 publications

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“…For the latter complexes (7-9), 1 H NMR spectra closely match those of the PMe 3 analogue, and characterization was not pursued further. 27,48,49 As has been noted by Jones and co-workers for the rhodium-based systems RhCp(L) and RhCp*(L) (L = PMe 3 , P(OMe) 3 ), 5 the equilibrium between η 2 -arene and C-H activated adducts depends on the extent of disruption to the π-system when dihaptocoordination occurs. Hence just as for RhCp*(PMe 3 ), the [(η 2 -R 2 C=CHR)]/[(R 2 C=CR)(H)] equilibrium ratio decreases as the ligand is adjusted from alkene to naphthalene to benzene.…”

Section: Substituent Effectsmentioning

confidence: 85%

“…Infrared and electrochemical data (Supporting Informaton) are similar to those reported previously for WTp(PMe 3 )(NO) (Br). 27 Treatment of 1 with sodium dispersed in benzene yields complex 2, isolated in 20% yield after chromatography. Complex 2 features an anodic wave in a cyclic voltammogram at E p,a = −0.16 V, which is consistent with data collected for the η 2 -bound benzene complex WTp(NO)(PMe 3 )(benzene) (cf.…”

Section: Synthesis and Equilibrium Studiesmentioning

confidence: 99%

“…Parenthetically, the anisole complex 3 can be prepared on a 15 g scale at 50% yield, a value comparable to that of the {WTp(NO) (PMe 3 )} analogue. 27 This complex is stable for months while stored as a solid at low temperatures (−30 °C). The substitution half-life of 3 at 25 °C is ~20 min, making it a suitable synthon for {WTp(NO)(PBu 3 )}, especially in cases where a potential ligand is incompatible with the reducing capability of sodium.…”

Section: Substituent Effectsmentioning

confidence: 99%

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Experiments and Direct Dynamics Simulations That Probe η²-Arene/Aryl Hydride Equilibria of Tungsten Benzene Complexes

et al. 2020

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Key steps in the functionalization of an unactivated arene often involve its dihaptocoordination by a transition metal followed by insertion into the C-H bond. However, rarely are the η 2 -arene and aryl hydride species in measurable equilibrium. In this study, the benzene/phenyl hydride equilibrium is explored for the {WTp(NO)(PBu 3 )} (Bu = n-butyl; Tp = trispyrazoylborate) system as a function of temperature, solvent, ancillary ligand, and arene substituent. Both face-flip and ring-walk isomerizations are identified through spin-saturation exchange measurements, which

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Section: Substituent Effectsmentioning

confidence: 85%

Section: Synthesis and Equilibrium Studiesmentioning

confidence: 99%

Section: Substituent Effectsmentioning

confidence: 99%

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Experiments and Direct Dynamics Simulations That Probe η²-Arene/Aryl Hydride Equilibria of Tungsten Benzene Complexes

et al. 2020

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“…Given that all the carbons in a benzene ring are unsaturated and that so many benzene derivatives are commercially available, approaches that utilize a benzene precursor as the C ‐ring could offer considerable diversity for medicinal chemists interested in exploring this scaffold. Our proposed route took advantage of the ability of benzene complex 1 , available on a 9 g scale, [38] and as either enantiomer, [39] to undergo an efficient sequence of reactions leading to the requisite cis ‐fused lactam ( Scheme 8). Use of the appropriate benzylamine in the lactamization would set the stage for a Heck coupling and hydrogenation to form the desired product ( 27 ).…”

Section: Introductionmentioning

confidence: 99%

Hydroamination of Dihapto‐Coordinated Benzene and Diene Complexes of Tungsten: Fundamental Studies and the Synthesis of γ‐Lycorane

Wilson

Nedzbala

Simpson

et al. 2021

Helvetica Chimica Acta

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Reactions are described for complexes of the form WTp(NO)(PMe3)(η2‐arene) and various amines, where the arene is benzene or benzene with an electron‐withdrawing substituent (CF3, SO2Ph, SO2Me). The arene complex is first protonated to form an η2‐arenium species, which then selectively adds the amine. The resulting η2‐5‐amino‐1,3‐cyclohexadiene complexes can then be subjected to the same sequence with a second nucleophile to form 3‐aminocyclohexene complexes, where up to three stereocenters originate from the arene carbons. Alternatively, 1,3‐cyclohexadiene complexes containing an ester group at the 5 position (also prepared from an arene) can be treated with acid followed by an amine to form trisubstituted 3‐aminocyclohexenes. When the amine is primary, ring closure can occur to form a cis‐fused bicyclic γ‐lactam. Highly functionalized cyclohexenes can be liberated from the tungsten through oxidative decomplexation. The potential utility of this methodology is demonstrated in the synthesis of the alkaloid γ‐lycorane. An enantioenriched synthesis of a lactam precursor to γ‐lycorane is also described. This compound is prepared from an enantioenriched version of the tungsten benzene complex. Regio‐ and stereochemical assignments for the reported compounds are supported by detailed 2D‐NMR analysis and 13 molecular structure determinations (SC‐XRD).

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“…45 These molecules, once coordinated, are activated towards hydrogenation, 43 electrophilic addition, 46 and cycloaddition reactions. 47 An important initial study indicated that an η 2 --coordinated benzene could be subjected to hydrogenation under mild temperatures and pressures ( Figure 10).…”

Section: 8b Dearomatization With [Os(nh3) 5 ] 2+ Fragmentmentioning

confidence: 99%

The Reactivity of eta-2-Aminoarenes Coordinated to Tungsten via Acid Trapping

Pienkos

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The Harman lab exploits π--basic metal fragments to functionalize arenes.Coordination of an aromatic molecule to a π--basic metal fragment usually occurs in an η 2 --fashion. In the process of complexation, the arenes are dearomatized, and the resulting ligands are able to undergo synthetic transformations that are inaccessible to the unbound, organic analogs. 1 Currently, the [TpW(NO)(PMe3)] metal fragment is used as a dearomatization reagent because of its low cost, scalability, and accessibility to a TpW(NO)(PMe3)(η 2 --benzene) complex. The η 2 --coordinated benzene can be substituted with a variety of aromatic ligands. 2 For example, an aromatic ring with an amine moiety can be exchanged with tungsten--bound benzene and protonated in situ, forming its conjugate acid ( Figure 1). This product, although cationic, is able to undergo a second electrophilic addition. Modifications of these bound arenes result in the formation of novel organometallic derivatives. Friedel--Crafts, 3 hydroamination, and cyclopropanation 4 reactions have been performed on these coordinated η 2 --aminoarenes. In some cases, after synthetic modifications, the functionalized ligand can be removed from the metal fragment.This strategy has been used to generate cyclohexenone, amidine, and hexahydroindole derivatives. References:( Introduction to Aromatic MoleculesAromatic compounds are a unique class of molecules due to their innate stability. 1 Originally, these molecules were distinguished from their hydrocarbon congeners based on their reactivity, as they formed substitution products instead of addition products when treated with electrophiles. For example, bromination of cyclooctateraene yields the dibrominated species, while benzene, under similar reaction conditions, yields the substituted species ( Figure 1). 2,3Figure 1: Bromination of Aromatic (above) and Non--aromatic Compounds (below) Benzene, the archetype of aromatic molecules, contains all sp 2 --hybridized carbons and exists in a planar arrangement. Its empirical formula, C:H, was known in 1825, but its structure was widely debated. 4--6 It was not until 1865 that Kekulé proposed a structure, which stood up to the test of time. 6 Since the discovery and characterization of benzene, many classes of aromatic molecules have been identified, some containing multicyclic ring systems and others containing heteroatoms. 7 A general criterion to characterize aromatic molecules is Hückel's rule, which states that for a compound to be aromatic it must contain a cyclic array of 4n+2 π-- Figure 6). 25 Figure 6: Cycloaddition Reactions with Aromatics Catalytic Dearomatization:In addition to promoting cycloaddition reactions, photochemical excitation allows for catalytic dearomatization of benzene with OsO4 to form an acetoxy--derivatized cyclohexane (Figure 7). 26 Other catalytic dearomatization reactions exploit benzylic halides, forming η 3 --allyic species with transition metals. 27--29 Following nucleophilic addition to these allyls, the arene substrat...

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Large-Scale Syntheses of Several Synthons to the Dearomatization Agent {TpW(NO)(PMe₃)} and Convenient Spectroscopic Tools for Product Analysis

Cited by 41 publications

References 16 publications

Experiments and Direct Dynamics Simulations That Probe η²-Arene/Aryl Hydride Equilibria of Tungsten Benzene Complexes

Experiments and Direct Dynamics Simulations That Probe η²-Arene/Aryl Hydride Equilibria of Tungsten Benzene Complexes

Hydroamination of Dihapto‐Coordinated Benzene and Diene Complexes of Tungsten: Fundamental Studies and the Synthesis of γ‐Lycorane

The Reactivity of eta-2-Aminoarenes Coordinated to Tungsten via Acid Trapping

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Large-Scale Syntheses of Several Synthons to the Dearomatization Agent {TpW(NO)(PMe3)} and Convenient Spectroscopic Tools for Product Analysis

Cited by 41 publications

References 16 publications

Experiments and Direct Dynamics Simulations That Probe η2-Arene/Aryl Hydride Equilibria of Tungsten Benzene Complexes

Experiments and Direct Dynamics Simulations That Probe η2-Arene/Aryl Hydride Equilibria of Tungsten Benzene Complexes

Hydroamination of Dihapto‐Coordinated Benzene and Diene Complexes of Tungsten: Fundamental Studies and the Synthesis of γ‐Lycorane

The Reactivity of eta-2-Aminoarenes Coordinated to Tungsten via Acid Trapping

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Product

Resources

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Large-Scale Syntheses of Several Synthons to the Dearomatization Agent {TpW(NO)(PMe₃)} and Convenient Spectroscopic Tools for Product Analysis

Experiments and Direct Dynamics Simulations That Probe η²-Arene/Aryl Hydride Equilibria of Tungsten Benzene Complexes

Experiments and Direct Dynamics Simulations That Probe η²-Arene/Aryl Hydride Equilibria of Tungsten Benzene Complexes