Reactions of free radicals with η3-allylpalladium(II) complexes: cyclohexyl radicals

Reid, Simon J.; Baird, Michael C.

doi:10.1016/j.jorganchem.2004.01.009

Cited by 5 publications

(3 citation statements)

References 47 publications

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“…Radical addition to Cp 2 Ti III ‐coordinated η 3 ‐allyl or η 3 ‐propargyl groups occurs selectively at the 2‐position, transforming the three‐electron XL‐type allyl into a four‐electron X 2 ‐type ligand in the titanacyclobutane or ‐cyclobutene products 113. Radical addition to Pd II –allyl complexes, on the other hand, appears to take place at the metal centre, although some of the final products result from allyl–alkyl coupling 34b,34c,35…”

Section: Radical Addition To Ligandsmentioning

confidence: 99%

Radical Coordination Chemistry and Its Relevance to Metal‐Mediated Radical Polymerization

Poli

2011

Eur J Inorg Chem

107

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The reactions engaged by organic radicals with transitionmetal complexes are reviewed with a particular focus on how they can interplay with and affect the results of radical polymerization. Radicals can either add to a metal centre to establish metal-carbon bonds, abstract an atom or group, be abstracted by an atom or group, undergo associative exchange, transfer a β-H atom or add to existing ligands in the metal coordination sphere. Reversibility is key for certain

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Section: Radical Addition To Ligandsmentioning

confidence: 99%

Radical Coordination Chemistry and Its Relevance to Metal‐Mediated Radical Polymerization

Poli

2011

Eur J Inorg Chem

107

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“…Insufficient fundamental knowledge of free radical reactions with ligands hinders their consideration in synthesis, even though free radicals are proposed intermediates in many transition metal mediated reactions including oxidative addition, chromium(II) complex reduction of organic halides, SmI 2 -induced coupling of organic halides with carbonyl compounds, and hydrogenation and hydrometalation of aromatic alkenes and conjugated dienes . Baird discovered unexpected allyl-derived product selectivity in competitive reactions of phenyl and trityl radicals with [Pd(η 3 -C 3 H 5 )(μ-Cl)] 2 , Pd(η 3 -C 3 H 5 )Cl(PPh 3 ), and [Pd(η 3 -C 3 H 5 )(PPh 3 ) 2 ]Cl . While [Pd(η 3 -C 3 H 5 )(μ-Cl)] 2 afforded exclusively kinetic product 3-phenylpropene, the phosphine derivatives provided 4,4,4-triphenyl-1-butene as sole allyl coupling product.…”

Section: Introductionmentioning

confidence: 99%

Allylnickel(II) and Allylpalladium(II) Derivatives of [(2-(Diphenylphosphino)ethyl)cyclopentadienyl]tricarbonylmetalates: Reactions with Free Radicals

et al. 2010

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The emerging utility of the bridging (2-(diphenylphosphino)ethyl)cyclopentadienyl (CpPPh) ligand to kinetically stabilize early-late metal−metal bonds to facilitate novel reactions in heterobimetallics is further established by the syntheses of four-legged piano stool M′{M(η3-L)}(CO)3(μ-η5:η1-CpPPh) (M′ = Cr, Mo, W; M = Ni, Pd; L = allyl, 2-methylallyl, cyclohexenyl). Complexes 1−3 (M = Ni, L = allyl) and 4−6 (M = Ni, L = 2-methylallyl) are the first structurally characterized heterobimetallics with transition metal−Ni(η3-allyl) units, while 7−9 (M = Ni, L = cyclohexenyl) are the only structurally characterized transition metal−Ni(η3-cyclohexenyl) complexes. Like Pd(η3-allyl)Cl(PPh3), 1−3 and 10−12 (M = Pd, L = allyl) respectively provide 4,4,4-triphenyl-1-butene as the sole allyl ligand coupling product from competitive reactions of phenyl and trityl radicals. However, while phenyl radical attack at the Pd(II) of Pd(η3-allyl)Cl(PPh3) is proposed as the first step in the trityl radical−allyl ligand coupling reaction, direct trityl radical attack at η3-allyl is strongly suggested in 1−3 and 10−12, respectively. A modest heterobimetallic effect may render the chromium complexes 1 and 10 more reactive with trityl radical than the tungsten complexes 3 and 12.

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“…The formation of C−C bonds by addition of free alkyl radicals to unsaturated organic substrates is a fundamental reaction in organic and polymer chemistry. , The coordination of such substrates to a metal should modify the energies of their radical addition reactions in one way or another, and this can provide new means to manipulate reactivity and selectivity in free radical chemistry. Indeed, there have been several studies in which a free alkyl radical has been added to arene, , allyl, , carbene, or other ligands coordinated to various transition metal complexes. In spite of a growing interest in this approach, there is still limited understanding of how coordination to a metal may influence the transition states and thermodynamics of radical addition reactions.…”

Section: Introductionmentioning

confidence: 99%

DFT Study of the Transition States and Products of Methyl Radical Addition to Olefins Coordinated in an Asymmetrical Mode to [Cp₂Zr(O^tBu)]⁺: Predictions of Reversed Regioselectivities Compared to the Noncoordinated Reactions

Hasanayn

El-Makkaoui

2009

Organometallics

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The addition of free alkyl radicals to olefins is known to encounter a small activation energy and to be highly regioselective, typically favoring the less substituted carbon of the double bond. The ability to modify the reactivity and regioselectivity of the given reaction can be of interest from both fundamental and practical perspectives. Olefins are known to bind to the [d 0 -Cp 2 Zr(O t Bu)] þ fragment (Zr) relatively weakly, affording adducts having a nonclassical asymmetrical bond between Zr and the double bond of the olefins. In the present study electronic structure methods based on density functional theory (B3LYP) have been used to investigate how the kinetics and thermodynamics of methyl radical addition to a systematically varied series of mono-and 1,1-disubstituted ethylene may change when they are coordinated to Zr. In general, methyl addition to the unsubstituted carbon of the coordinated olefins is found to encounter an increased activation energy compared to the noncoordinated reactions. In contrast, the barriers of addition to the substituted carbon of the coordinated olefins are slightly smaller than the barriers in the noncoordinated reactions. These effects lead to opposite regioselectivities in the free and the coordinated reactions of several olefins. However, even when the kinetic regioselectivity reverses upon coordination, the thermodynamic preference for addition to the terminal carbon in the noncoordinated reactions remains unchanged. These results are discussed qualitatively on the basis of unconventional geometries calculated in the coordinated reactants, transition states, and products.

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Reactions of free radicals with η3-allylpalladium(II) complexes: cyclohexyl radicals

Cited by 5 publications

References 47 publications

Radical Coordination Chemistry and Its Relevance to Metal‐Mediated Radical Polymerization

Radical Coordination Chemistry and Its Relevance to Metal‐Mediated Radical Polymerization

Allylnickel(II) and Allylpalladium(II) Derivatives of [(2-(Diphenylphosphino)ethyl)cyclopentadienyl]tricarbonylmetalates: Reactions with Free Radicals

DFT Study of the Transition States and Products of Methyl Radical Addition to Olefins Coordinated in an Asymmetrical Mode to [Cp₂Zr(O^tBu)]⁺: Predictions of Reversed Regioselectivities Compared to the Noncoordinated Reactions

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Reactions of free radicals with η3-allylpalladium(II) complexes: cyclohexyl radicals

Cited by 5 publications

References 47 publications

Radical Coordination Chemistry and Its Relevance to Metal‐Mediated Radical Polymerization

Radical Coordination Chemistry and Its Relevance to Metal‐Mediated Radical Polymerization

Allylnickel(II) and Allylpalladium(II) Derivatives of [(2-(Diphenylphosphino)ethyl)cyclopentadienyl]tricarbonylmetalates: Reactions with Free Radicals

DFT Study of the Transition States and Products of Methyl Radical Addition to Olefins Coordinated in an Asymmetrical Mode to [Cp2Zr(OtBu)]+: Predictions of Reversed Regioselectivities Compared to the Noncoordinated Reactions

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DFT Study of the Transition States and Products of Methyl Radical Addition to Olefins Coordinated in an Asymmetrical Mode to [Cp₂Zr(O^tBu)]⁺: Predictions of Reversed Regioselectivities Compared to the Noncoordinated Reactions