Catalysis Involving the H• Transfer Reactions of First‐Row Transition Metals

Hartung, J. B.; Norton, Jack R.

doi:10.1002/9783527631582.ch1

Cited by 23 publications

(28 citation statements)

References 114 publications

(111 reference statements)

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“…45 Halpern proposed sequential HAT events from in situ generated (CO) 4 CoH during the reduction of anthracene 46 and in the hydrogenation of α-methylstyrene with (CO) 5 MnH. 47 HAT pathways have also been proposed in alkene reductions with chromium, 48,49 tungsten, 50 and vanadium 51 hydrides.…”

Section: Resultsmentioning

confidence: 99%

Catalytic Hydrogenation Activity and Electronic Structure Determination of Bis(arylimidazol-2-ylidene)pyridine Cobalt Alkyl and Hydride Complexes

et al. 2013

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The bis(arylimidazol-2-ylidene)pyridine cobalt methyl complex, (iPrCNC)CoCH3, was evaluated for the catalytic hydrogenation of alkenes. At 22 °C and 4 atm of H2 pressure, (iPrCNC)CoCH3 is an effective pre-catalyst for the hydrogenation of sterically hindered, unactivated alkenes such as trans-methylstilbene, 1-methyl-1-cyclohexene and 2,3-dimethyl-2-butene, representing one of the most active cobalt hydrogenation catalysts reported to date. Preparation of the cobalt hydride complex, (iPrCNC)CoH was accomplished by hydrogenation of (iPrCNC)CoCH3. Over the course of 3 hours at 22 °C, migration of the metal-hydride to the 4-position of the pyridine ring yielded (4-H2-iPrCNC)CoN2. Similar alkyl migration was observed upon treatment of (iPrCNC)CoH with 1,1-diphenylethylene. This reactivity raised the question as to whether this class of chelate is redoxactive, engaging in radical chemistry with the cobalt center. A combination of structural, spectroscopic and computational studies was conducted and provided definitive evidence for bis(arylimidazol-2-ylidene)pyridine radicals in reduced cobalt chemistry. Spin density calculations established that the radicals were localized on the pyridine ring, accounting for the observed reactivity and suggest a wide family of pyridine-based pincers may also be redox active.

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Section: Resultsmentioning

confidence: 99%

Catalytic Hydrogenation Activity and Electronic Structure Determination of Bis(arylimidazol-2-ylidene)pyridine Cobalt Alkyl and Hydride Complexes

et al. 2013

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“…The metal center, ligand, and substrate can influence the preference for pathways 1−3 by altering the relative stabilities of organic, metallic, and organometallic intermediates. 11f,g In our bimetallic system, it was unclear which Co−H HAT pathway, formation of a solvent-separated radical (Scheme 1, pathway 1) or discrete organometallic (Scheme 1, pathway 3), was relevant to the catalytic cycle and could interact productively with a catalytically generated nickel species.…”

Section: Introductionmentioning

confidence: 93%

“…Initial insights were drawn from our recent connection between Drago−Mukaiyama hydrofunctionalization reactions catalyzed by cobalt, manganese, and iron hydrides to the paradigm of MHAT explored by Simandi and Nagy, 7 Kwiatek, 8 Jackman, 9 Halpern, 10 Norton, 11 and others. 12…”

Section: Introductionmentioning

confidence: 99%

Mechanistic Interrogation of Co/Ni-Dual Catalyzed Hydroarylation

2018

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Cobalt/nickel-dual catalyzed hydroarylation of terminal olefins with iodoarenes builds complexity from readily available starting materials, with a high preference for the Markovnikov (branched) product. Here, we advance a mechanistic model of this reaction through the use of reaction progress kinetic analysis (RPKA), radical clock experiments, and stoichiometric studies. Through exclusion of competing hypotheses, we conclude that the reaction proceeds through an unprecedented alkylcobalt to nickel direct transmetalation. Demonstration of catalytic alkene prefunctionalization, via spectroscopic observation of an organocobalt species, distinguishes this Csp-Csp cross-coupling method from a conventional transmetalation process, which employs a stoichiometric organometallic nucleophile, and from a bimetallic oxidative addition of an organohalide across nickel, described by radical scission and subsequent alkyl radical capture at a second nickel center. A refined understanding of the reaction leads to an optimized hydroarylation procedure that excludes exogenous oxidant, demonstrating that the transmetalation is net redox neutral. Catalytic alkene prefunctionalization by cobalt and engagement with nickel catalytic cycles through direct transmetalation provides a new platform to merge these two rich areas of chemistry in preparatively useful ways.

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“…2,3 In contrast, Jack and many others have pioneered the understanding and application of alternative reaction pathways: the non-canonical radical reactions of metal hydrides, or hydrogen atom transfer (HAT) reactions. 4 …”

Section: Introductionmentioning

confidence: 99%

Mn-, Fe-, and Co-Catalyzed Radical Hydrofunctionalizations of Olefins

et al. 2016

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Cofactor-mimetic aerobic oxidation has conceptually merged with catalysis of syngas reactions to form a wide range of Markovnikov-selective olefin radical hydrofunctionalizations. We cover the development of the field and review contributions to reaction invention, mechanism and application to complex molecule synthesis. We also provide a mechanistic framework for understanding this compendium of radical reactions.

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Catalysis Involving the H• Transfer Reactions of First‐Row Transition Metals

Cited by 23 publications

References 114 publications

Catalytic Hydrogenation Activity and Electronic Structure Determination of Bis(arylimidazol-2-ylidene)pyridine Cobalt Alkyl and Hydride Complexes

Catalytic Hydrogenation Activity and Electronic Structure Determination of Bis(arylimidazol-2-ylidene)pyridine Cobalt Alkyl and Hydride Complexes

Mechanistic Interrogation of Co/Ni-Dual Catalyzed Hydroarylation

Mn-, Fe-, and Co-Catalyzed Radical Hydrofunctionalizations of Olefins

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