Detection of Palladium(I) in Aerobic Oxidation Catalysis

Jaworski, Jonathan N.; McCann, Scott D.; Guzei, Ilia A.; Stahl, Shannon S.

doi:10.1002/anie.201700345

Cited by 57 publications

(48 citation statements)

References 88 publications

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“…In recent years, the involvement of Pd(I) complexes in catalytically relevant coupling processes has attracted a lot of attention. [39][40][41][42][43][44] They may open up new mechanistic alternatives to the common operating routes. However, in most cases they play a role of a source of reactive Pd(0) species, as we believe it is the case here.…”

Section: Reactions Of [Pd( 3 -Allyl)cl(pph3)] Under Conditions Relevamentioning

confidence: 99%

Palladium-Catalyzed Aerobic Homocoupling of Alkynes: Full Mechanistic Characterization of a More Complex Oxidase-Type Behavior

et al. 2018

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A combined experimental and computational approach has been used to shed light on the mechanism of the Pdcatalyzed oxidative homocoupling of alkynes using oxygen as oxidant. Mechanistic understanding is important because of the synthetically relevant direct involvement of oxygen in the oxidative coupling, and because of the presence of related processes as undesired side reactions in cross-coupling reactions involving terminal alkynes. A low-ligated [Pd(PPh3)(alkyne)] complex is key in the process and it can be conveniently generated from allylic palladium(II) complexes in the presence of a base or from Pd(I) allylic dimers as precatalysts. The catalytic coupling occurs by alkyne metalation to give an anionic [Pd(PPh3)(alkynyl)]complex that is then oxidized by oxygen. The interaction of oxygen occurs only on this electron rich Pd(0) anionic species and leads to a 2-peroxo palladium(II) singlet intermediate that undergoes subsequent protonolysis to a 1-hydroperoxide palladium(II) complex. The second alkyne metalation occurs on the Pd(II) hydroperoxo derivative, this ligand acting as an internal base, to give a bis(alkynyl)Pd(II) complex that evolves to the product by reductive elimination as the product-forming step. This reaction is an oxidase-type process that, in contrast to most Pd-catalyzed oxidative processes, occurs without separation of the substrate transformation and the catalyst oxidation, both processes being intertwined and dependent of one another.

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Section: Reactions Of [Pd( 3 -Allyl)cl(pph3)] Under Conditions Relevamentioning

confidence: 99%

Palladium-Catalyzed Aerobic Homocoupling of Alkynes: Full Mechanistic Characterization of a More Complex Oxidase-Type Behavior

et al. 2018

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“…Therefore, a comproportionation process producing an equilibrium between the Pd(I) π–allyl dimer and the mononuclear complexes was also identified, demonstrating that the Pd(I) dimer 7c forms as an off-cycle product. Several studies identifying a dinuclear Pd(I) complex as the resting state outside of the catalytic cycle have also been reported [ 64 , 65 , 66 , 67 ].…”

Section: Catalytic Applicationsmentioning

confidence: 99%

Dinuclear Nickel(I) and Palladium(I) Complexes for Highly Active Transformations of Organic Compounds

2018

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In typical catalytic organic transformations, transition metals in catalytically active complexes are present in their most stable valence states, such as palladium(0) and (II). However, some dimeric monovalent metal complexes can be stabilized by auxiliary ligands to form diamagnetic compounds with metal–metal bonding interactions. These diamagnetic compounds can act as catalysts while retaining their dimeric forms, split homolytically or heterolytically into monomeric forms, which usually have high activity, or in contrast, become completely deactivated as catalysts. Recently, many studies using group 10 metal complexes containing nickel and palladium have demonstrated that under specific conditions, the active forms of these catalyst precursors are not mononuclear zerovalent complexes, but instead dinuclear monovalent metal complexes. In this mini-review, we have surveyed the preparation, reactivity, and the catalytic processes of dinuclear nickel(I) and palladium(I) complexes, focusing on mechanistic insights into the precatalyst activation systems and the structure and behavior of nickel and palladium intermediates.

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“…Further, these two factors also promote the productive off-cycle activation of the catalyst, which involves the formal reduction of the Pd(II) precatalyst to the Pd(0) active species. The in-situ generation of the Pd(0) highly reactive species can also promote further off-cycle chemistry, including the formation of dimers, 45,46,47,48 trimers, 49,50 nanoparticles 51 or Pd-black, 52 which can be detrimental to catalysis. However, when properly formulated, polynuclear complexes can also be highly efficient cross-coupling precatalysts.…”

mentioning

confidence: 99%

Designing Pd and Ni Catalysts for Cross-Coupling Reactions by Minimizing Off-Cycle Species

Balcells

Nova

2018

ACS Catal.

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This perspective presents an overview on recent experimental and computational studies on the off-cycle reactions of palladium-and nickel-catalyzed cross-couplings. Several reactions entering or leaving the catalytic cycle have been characterized, including the activation of Pd(II) precatalysts by H-shift and the deactivation of Ni(II) precatalysts by comproportionation. A fundamental difference between the off-cycle chemistries of palladium and nickel is the larger diversity of species yielded by the latter, with a rich combination of different oxidation states, nuclearity and ligand coordination modes. The molecular-level understanding of off-cycle reactions has enabled new catalyst design strategies, including the stereoelectronic fine-tuning of the ligands aimed at maximizing the activation of the precatalyst meanwhile preventing its deactivation. Despite several challenges, which concern both experiments (e.g. isolation and characterization of transient species) and computations (e.g. comprehensive mapping of the potential energy surface), this approach has already been applied with success in the optimization of popular catalytic platforms (e.g. NHC-Pd-allyl precatalysts) and shows promise for the development of highly active and robust catalysts based on nickel.

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Detection of Palladium(I) in Aerobic Oxidation Catalysis

Cited by 57 publications

References 88 publications

Palladium-Catalyzed Aerobic Homocoupling of Alkynes: Full Mechanistic Characterization of a More Complex Oxidase-Type Behavior

Palladium-Catalyzed Aerobic Homocoupling of Alkynes: Full Mechanistic Characterization of a More Complex Oxidase-Type Behavior

Dinuclear Nickel(I) and Palladium(I) Complexes for Highly Active Transformations of Organic Compounds

Designing Pd and Ni Catalysts for Cross-Coupling Reactions by Minimizing Off-Cycle Species

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