Cycloneophylpalladium(IV) Complexes: Formation by Oxidative Addition and Selectivity of Their Reductive Elimination Reactions

Behnia, Ava; Fard, Mahmood Azizpoor; Blacquiere, Johanna M.; Puddephatt, Richard J.

doi:10.1021/acs.organomet.0c00615

Cited by 12 publications

(10 citation statements)

References 66 publications

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“…These catalytic intermediates can form via oxidation of M(II) and M(III) complexes ,,, or even via oxidative addition of RX electrophiles to Pd(II) complexes. − Organometallic complexes Pd(IV) and Ni(IV) are usually more stable than similar complexes of Pd(III) and Ni(III). Many well-defined Pd(IV) complexes containing chelated ligands coordinated to palladium via Pd–C(sp 2 ) or Pd–C(sp 3 ) bonds have been prepared, and reductive elimination of these complexes to give C–C and C–X coupling products was studied in detail. ,− …”

Section: Main Partmentioning

confidence: 99%

Nickel and Palladium Catalysis: Stronger Demand than Ever

2022

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Key similarities and differences of Pd and Ni in catalytic systems are discussed. Overall, Ni and Pd catalyze a vast number of similar C−C and C−heteroatom bond-forming reactions. However, the smaller atomic radius and lower electronegativity of Ni, as well as the more negative redox potentials of low-valent Ni species, often provide higher reactivity of Ni systems in oxidative addition or insertion reactions and higher persistence of alkyl-Ni intermediates against β-hydrogen elimination, thus enabling activation of more reluctant electrophiles, including alkyl electrophiles. Another key point relates to the higher stability of the open-shell electronic configurations of Ni(I) and Ni(III) compared with Pd(I) and Pd(III). Nickel systems very often involve a number of interconvertible Ni (n+) active species of variable oxidation states (Ni(0), Ni(I), Ni(II), and Ni(III)). In contrast, catalytic reactions involving Pd(I) or Pd(III) active species are still relatively less developed and may require facilitation by special ligands or merging with photo-or electrocatalysis. However, the relatively high redox potentials of Pd (n+) species ensure their facile reduction to Pd (0) species under the assistance of numerous reagents or solvents, providing relatively high concentrations of molecular Pd 1 (0) complexes that can reversibly aggregate into active Pd n clusters and nanoparticles to form a cocktail of interconvertible Pd n (0) active species of various nuclearities (i.e., various values of "n"). Nickel systems involving Ni(0) complexes often require special strong reductants; they are more sensitive to deactivation by air and other oxidizers and, as consequence, often operate at higher catalyst loadings than palladium systems in the same reactions. The ease of activation and relatively high stability of low-valent active Pd species provide high robustness and versatility for palladium catalysis, whereas a variety of Ni oxidation states enables more diverse and uncommon reactivity, albeit requiring higher efforts in the activation and stabilization of nickel catalytic systems. As a point for discussion, we may note that Pd catalytic systems may easily form a "cocktail of particles" of different nuclearities but similar oxidation states (Pd 1 , Pd n , Pd NPs), whereas nickel may behave as a "cocktail of species" in different oxidation states but is less variable in stable nuclearities. Undoubtedly, there is stronger demand than ever not only to develop improved efficient catalysts but also to understand the mechanisms of Pd and Ni catalytic systems.

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Section: Main Partmentioning

confidence: 99%

Nickel and Palladium Catalysis: Stronger Demand than Ever

2022

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“…It follows that oxidation and reduction reactions can be promoted by changes in coordination numbers. For example, reduction of six-coordinate octahedral Pd(IV) or Pt(IV) complexes occurs more readily after ligand loss affords a five-coordinate intermediate. − There are several studies of oxidation/reduction chemistry with complexes containing SRLs that change coordination mode depending on the oxidation state of the metal. − Even challenging small molecule reduction (e.g., of N 2 , PhN = NPh or O 2 ) can be achieved by metals (e.g., Mo(III) or W(II)), in which the SRL stabilizes a masked low-coordinate structure. , …”

Section: Influence Of Srls On Fundamental Organometallic Reactionsmentioning

confidence: 99%

Structurally-Responsive Ligands for High-Performance Catalysts

Blacquiere

2021

ACS Catal.

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Hemilabile ligands that undergo reversible changes in denticity have long been exploited to enable catalyst activation and to increase lifetime. However, this common description does not fully reflect reality with respect to the diversity of known ligand types, modes of action, and impacts on catalysis. The term structurally responsive ligand (SRL) is employed here to encompass ligands that exhibit selftuning denticity, hapticity, or versatile coordination. This Perspective covers case study examples of SRLs in catalysis and their influence on catalyst lifetime, rate, and selectivity. The examples include leading and emerging catalysts for enabling transformations, which emphasizes both the breadth and significance of this class of ligands.

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“…The hemilabile ligands RO(CH 2 ) 3 N(CH 2 -2-C 5 H 4 N) 2 , L1, R = H, or L2, R = Me, 30,31 and their cycloneophylpalladium (II) complexes 1 and 2 (Scheme 4) have been reported previously. [32][33][34][35][36] The preferred isomers exhibit bidentate ligand coordination with a 5-membered chelate. [34][35][36] The major isomers, 1a or 2a, have the aryl group trans to the pyridyl donor, structures which are slightly lower in energy than 1b or 2b with the aryl group trans to the tertiary amine donor.…”

Section: Introductionmentioning

confidence: 99%