Mechanisms of the hydrometalation (insertion) and stoichiometric hydrogenation reactions of conjugated dienes effected by manganese pentacarbonyl hydride: processes involving the radical pair mechanism

Wassink, Berend; Thomas, Marian J.; Wright, Steven; Gillis, Daniel; Baird, Michael C.

doi:10.1021/ja00241a016

Cited by 41 publications

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“…[42] Hydrogen-atom transfer from the metal hydride is an alternative mechanism that has been observed for metal hydrides with small M À H bond dissociation enthalpies and when the resulting organic radical is particularly stable (Scheme 2c). [43][44][45][46][47][48][49][50][51] Hydrogenation and hydroformylation of styrene catalyzed by [HCo(CO) 4 ] was confirmed to involve a hydrogen-atom transfer mechanism by observing chemically induced dynamic nuclear polarization (CIDNP) from radical pairs in these processes. [51] Tables 2 and 3 and illustrated in Figures 2 and 3.…”

Section: Hydrogen-atom Transfer Between [Co III (H)a C H T U N G T R mentioning

confidence: 99%

Hydrogen‐Atom Transfer in Reactions of Organic Radicals with [Co^II(por)]^. (por=Porphyrinato) and in Subsequent Addition of [Co(H)(por)] to Olefins

Bruin

Dzik

et al. 2009

Chemistry A European J

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The mechanisms for hydrogen-atom transfer from the cyanoisopropyl radical (*)C(CH(3))(2)CN to [Co(II)(por)](*) (yielding [Co(III)(H)(por)] and CH(2)=C(CH(3))(CN); por = porphyrinato) and the insertion of vinyl acetate (CH(2)=CHOAc) into the Co-H bond of [Co(H)(por)] (giving [Co(III){CH(OAc)CH(3)}(por)]) were investigated by DFT calculations. The results are compared with experimental data. These reactions are relevant to catalytic chain transfer (CCT) in radical polymerization of olefins mediated by [Co(II)(por)](*), the formation and homolysis of organo-cobalt complexes that mediate living radical polymerization of vinyl acetate, and cobalt-mediated hydrogenation of olefins. Hydrogen transfer from (*)C(CH(3))(2)CN to [Co(II)(por)](*) proceeds via a single transition state that has structural features resembling the products [Co(H)(por)] and CH(2)=C(CH(3))CN. The separated radicals approach to form a close-contact radical pair and then pass through the transition state for hydrogen-atom transfer to form [Co(III)(H)(por)] and CH(2)=C(CH(3))CN. This process provides a very low overall barrier for the hydrogen-atom transfer reaction (DeltaG(double dagger) = +3.8 kcal mol(-1)). The reverse reaction corresponding to the addition of [Co(H)(por)] to CH(2)=C(CH(3))CN has a low barrier (DeltaG(double dagger) = +8.9 kcal mol(-1)) as well. Insertion of vinyl acetate into the Co-H bond of [Co(III)(H)(por)] also proceeds over a low barrier (DeltaG(double dagger) = +11.4 kcal mol(-1)) hydrogen-transfer step from [Co(III)(H)(por)] to a carbon atom of the alkene to produce a close-contact radical pair. Dissociation of the radical pair, reorientation, and radical-radical coupling to form an organo-cobalt complex are the culminating steps in the net insertion of an olefin into the Co-H bond. The computed energies obtained for the hydrogen-atom transfer reactions from (*)C(CH(3))(2)CN to [Co(II)(por)](*) and from [Co(H)(por)] to olefins, as well as the organo-cobalt bond homolysis energies correspond well with the experimental observations. The mechanism of alkene insertion into the Co-H bond of [Co(III)(H)(por)] is of general interest, because the species does not contain any cis-vacant sites to the hydride and the usual migratory insertion pathway is not available. The low barrier predicted here for the multistep insertion process suggests that (depending on the bond strengths) even for systems that do have a cis-vacant site, the radical-type insertion might compete with classical migratory insertion.

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Section: Hydrogen-atom Transfer Between [Co III (H)a C H T U N G T R mentioning

confidence: 99%

Hydrogen‐Atom Transfer in Reactions of Organic Radicals with [Co^II(por)]^. (por=Porphyrinato) and in Subsequent Addition of [Co(H)(por)] to Olefins

Bruin

Dzik

et al. 2009

Chemistry A European J

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“…Transition-metal hydride complexes can serve as important intermediates in the catalytic transfer of protons, hydrogen atoms, − hydrides, − or electrons − to substrates from H 2 gas. A comprehensive understanding of their chemistry is essential for explaining existing catalytic reactions and for the rational design of new ones.…”

Section: Introductionmentioning

confidence: 99%

Transition-Metal Hydride Radical Cations

Shaw

Estes

et al. 2016

Chem. Rev.

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Transition-metal hydride radical cations (TMHRCs) are involved in a variety of chemical and biochemical reactions, making a more thorough understanding of their properties essential for explaining observed reactivity and for the eventual development of new applications. Generally, these species may be treated as the ones formed by one-electron oxidation of diamagnetic analogues that are neutral or cationic. Despite the importance of TMHRCs, the generally sensitive nature of these complexes has hindered their development. However, over the last four decades, many more TMHRCs have been synthesized, characterized, isolated, or hypothesized as reaction intermediates. This comprehensive review focuses on experimental studies of TMHRCs reported through the year 2014, with an emphasis on isolated and observed species. The methods used for the generation or synthesis of TMHRCs are surveyed, followed by a discussion about the stability of these complexes. The fundamental properties of TMHRCs, especially those pertaining to the M-H bond, are described, followed by a detailed treatment of decomposition pathways. Finally, reactions involving TMHRCs as intermediates are described.

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“…1,2 Early reports employed stoichiometric amounts of metal hydrides and activated alkenes. [3][4][5][6][7][8][9][10][11][12][13] Recently a range of exceptionally useful alkene hydrofunctionalization reactions have been recorded by Mukaiyama, Carreira, Boger, Baran, and others using cobalt-, manganese-, and iron-based catalysts (Scheme 1a). Reports from our laboratory and Shenvi and co-workers detail methods for the reduction of alkenyl halides 43,44 and unactivated alkenes 44 by hydrogen atom transfer.…”

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confidence: 99%

Non-classical selectivities in the reduction of alkenes by cobalt-mediated hydrogen atom transfer

Herzon

2015

Chem. Sci.

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Mechanisms of the hydrometalation (insertion) and stoichiometric hydrogenation reactions of conjugated dienes effected by manganese pentacarbonyl hydride: processes involving the radical pair mechanism

Cited by 41 publications

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Hydrogen‐Atom Transfer in Reactions of Organic Radicals with [Co^II(por)]^. (por=Porphyrinato) and in Subsequent Addition of [Co(H)(por)] to Olefins

Hydrogen‐Atom Transfer in Reactions of Organic Radicals with [Co^II(por)]^. (por=Porphyrinato) and in Subsequent Addition of [Co(H)(por)] to Olefins

Transition-Metal Hydride Radical Cations

Non-classical selectivities in the reduction of alkenes by cobalt-mediated hydrogen atom transfer

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Mechanisms of the hydrometalation (insertion) and stoichiometric hydrogenation reactions of conjugated dienes effected by manganese pentacarbonyl hydride: processes involving the radical pair mechanism

Cited by 41 publications

References 0 publications

Hydrogen‐Atom Transfer in Reactions of Organic Radicals with [CoII(por)]. (por=Porphyrinato) and in Subsequent Addition of [Co(H)(por)] to Olefins

Hydrogen‐Atom Transfer in Reactions of Organic Radicals with [CoII(por)]. (por=Porphyrinato) and in Subsequent Addition of [Co(H)(por)] to Olefins

Transition-Metal Hydride Radical Cations

Non-classical selectivities in the reduction of alkenes by cobalt-mediated hydrogen atom transfer

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Product

Resources

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Hydrogen‐Atom Transfer in Reactions of Organic Radicals with [Co^II(por)]^. (por=Porphyrinato) and in Subsequent Addition of [Co(H)(por)] to Olefins

Hydrogen‐Atom Transfer in Reactions of Organic Radicals with [Co^II(por)]^. (por=Porphyrinato) and in Subsequent Addition of [Co(H)(por)] to Olefins