Ate Complexes in Iron‐Catalyzed Cross‐Coupling Reactions

Parchomyk, Tobias; Koszinowski, Konrad

doi:10.1002/chem.201603574

Cited by 41 publications

(53 citation statements)

References 48 publications

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“…Being highly electropositive, lithium and magnesium readily form cations, whereas more electronegative cobalt strongly prefers anionic ate complexes. Very similar behavior has previously been observed for the transmetalation of iron, copper, and zinc precursors as well.…”

Section: Resultssupporting

confidence: 83%

“…The formation of these Co III complexes upon the transmetalation of a Co II precursor may seem surprising. However, similar behavior has been found for the transmetalation of iron precursors and has been rationalized by redox disproportionation reactions of the primarily produced organoiron species . The detected Co III complexes probably resulted from analogous reactions.…”

Section: Resultsmentioning

confidence: 99%

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Low‐Valent Ate Complexes Formed in Cobalt‐Catalyzed Cross‐Coupling Reactions with 1,3‐Dienes as Additives

Kreyenschmidt

Koszinowski

2017

Chemistry A European J

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The combination of CoCl and 1,3-dienes is known to catalyze challenging alkyl-alkyl cross-coupling reactions between Grignard reagents and alkyl halides, but the mechanism of these valuable transformations remains speculative. Herein, electrospray-ionization mass spectrometry is used to identify and characterize the elusive intermediates of these and related reactions. The vast majority of detected species contain low-valent cobalt(I) centers and diene molecules. Charge tagging, deuterium labeling, and gas-phase fragmentation experiments elucidate the likely origin of these species and show that the diene not only binds to Co as a π ligand, but also undergoes migratory insertion reactions into Co-H and Co-R bonds. The resulting species have a strong tendency to form anionic cobalt(I) ate complexes, the superior nucleophilicity of which should render them highly reactive toward electrophilic substrates and, thus, presumably is the key to the high catalytic efficiency of the system under investigation. Upon the reaction of the in situ formed cobalt(I) ate complexes with organyl halides, only the final cross-coupling product could be detected, but no cobalt(III) species. This finding implies that this reaction step proceeds in a direct manner without any intermediate or, alternatively, that it involves an intermediate with a very short lifetime.

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Section: Resultssupporting

confidence: 83%

Section: Resultsmentioning

confidence: 99%

Low‐Valent Ate Complexes Formed in Cobalt‐Catalyzed Cross‐Coupling Reactions with 1,3‐Dienes as Additives

Kreyenschmidt

Koszinowski

2017

Chemistry A European J

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“…Given the anionic nature of the putative catalyst species, we also used negative‐ion mode ESI‐MS for their selective detection and analysis. Under carefully optimized conditions, this method is capable of detecting even highly reactive organometallics in intact form, including low‐valent transition‐metal complexes . Indeed, negative‐ion mode ESI of a solution of 1 in THF afforded the free [Co(anthracene) 2 ] − anion with high signal intensity (Figure S6 in the Supporting Information).…”

Section: Resultsmentioning

confidence: 99%

Alkene Metalates as Hydrogenation Catalysts

Büschelberger

Gärtner

Reyes-Rodriguez

et al. 2017

Chemistry A European J

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First‐row transition‐metal complexes hold great potential as catalysts for hydrogenations and related reductive reactions. Homo‐ and heteroleptic arene/alkene metalates(1−) (M=Co, Fe) are a structurally distinct catalyst class with good activities in hydrogenations of alkenes and alkynes. The first syntheses of the heteroleptic cobaltates [K([18]crown‐6)][Co(η4‐cod)(η2‐styrene)2] (5) and [K([18]crown‐6)][Co(η4‐dct)(η4‐cod)] (6), and the homoleptic complex [K(thf)2][Co(η4‐dct)2] (7; dct=dibenzo[a,e]cyclooctatetraene, cod=1,5‐cyclooctadiene), are reported. For comparison, two cyclopentadienylferrates(1−) were synthesized according to literature procedures. The isolated and fully characterized monoanionic complexes were competent precatalysts in alkene hydrogenations under mild conditions (2 bar H2, r.t., THF). Mechanistic studies by NMR spectroscopy, ESI mass spectrometry, and poisoning experiments documented the operation of a homogeneous mechanism, which was initiated by facile redox‐neutral π‐ligand exchange with the substrates followed by H2 activation. The substrate scope of the investigated precatalysts was also extended to polar substrates (ketones and imines).

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“…This impressive study complements earlier work that had already pointed at iron-ate species as possible intermediates whenever groups unable to undergo β-hydride elimination are to be transferred. 90−93 Related studies were devoted to the mechanism of phenyl transfer to alkyl halide partners catalyzed by iron complexes endowed with phosphine ligands: 94 while an Fe(0) as well as an Fe(II) species were both found able of effecting the C–C coupling step, their kinetic competences proved largely different. In contrast, Fe(I) complexes, which were prominently advocated elsewhere as causative agents, 95,96 basically proved incompetent.…”

Section: The Analytical Frontiermentioning

confidence: 99%

Iron Catalysis in Organic Synthesis: A Critical Assessment of What It Takes To Make This Base Metal a Multitasking Champion

2016

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The current status of homogeneous iron catalysis in organic chemistry is contemplated, as are the reasons why this particular research area only recently starts challenging the enduring dominance of the late and mostly noble metals over the field. Centered in the middle of the d-block and able to support formal oxidation states ranging from −II to +VI, iron catalysts hold the promise of being able to encompass organic synthesis at large. They are expected to serve reductive as well as oxidative regimes, can emulate “noble tasks”, but are also able to adopt “early” transition metal character. Since a comprehensive coverage of this multidimensional agenda is beyond the scope of an Outlook anyway, emphasis is laid in this article on the analysis of the factors that perhaps allow one to control the multifarious chemical nature of this earth-abundant metal. The challenges are significant, not least at the analytical frontier; their mastery mandates a mindset that differs from the routines that most organic chemists interested in (noble metal) catalysis tend to cultivate. This aspect notwithstanding, it is safe to predict that homogeneous iron catalysis bears the chance to enable a responsible paradigm for chemical synthesis and a sustained catalyst economy, while potentially providing substantial economic advantages. This promise will spur the systematic and in-depth investigations that it takes to upgrade this research area to strategy-level status in organic chemistry and beyond.

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Ate Complexes in Iron‐Catalyzed Cross‐Coupling Reactions

Cited by 41 publications

References 48 publications

Low‐Valent Ate Complexes Formed in Cobalt‐Catalyzed Cross‐Coupling Reactions with 1,3‐Dienes as Additives

Low‐Valent Ate Complexes Formed in Cobalt‐Catalyzed Cross‐Coupling Reactions with 1,3‐Dienes as Additives

Alkene Metalates as Hydrogenation Catalysts

Iron Catalysis in Organic Synthesis: A Critical Assessment of What It Takes To Make This Base Metal a Multitasking Champion

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