镍和钯催化：比以往更强劲的需求,ACS Catalysis

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镍和钯催化：比以往更强劲的需求
ACS Catalysis ( IF 11.3 ) Pub Date : 2022-01-05 , DOI: 10.1021/acscatal.1c04705
Victor M. Chernyshev ₁ , Valentine P. Ananikov _{1,

2}

Affiliation

讨论了催化体系中 Pd 和 Ni 的主要异同。总体而言，Ni 和 Pd 催化了大量类似的 C-C 和 C-杂原子键形成反应。然而，Ni 的较小的原子半径和较低的电负性，以及低价 Ni 物种的更负的氧化还原电位，通常使 Ni 系统在氧化加成或插入反应中具有更高的反应性，并且烷基-Ni 中间体对 β 具有更高的持久性-氢消除，从而能够激活更不情愿的亲电体，包括烷基亲电体。另一个关键点是与 Pd(I) 和 Pd(III) 相比，Ni(I) 和 Ni(III) 的开壳电子构型具有更高的稳定性。镍系统经常涉及许多可相互转换的 Ni ^{( n +)}可变氧化态的活性物质（Ni(0)、Ni(I)、Ni(II) 和 Ni(III)）。相比之下，涉及 Pd(I) 或 Pd(III) 活性物质的催化反应仍然相对较少发展，可能需要特殊配体促进或与光催化或电催化结合。然而，Pd ^{( n +)}物种相对较高的氧化还原电位确保它们在众多试剂或溶剂的帮助下容易还原为 Pd ⁽⁰⁾物种，提供相对高浓度的分子 Pd ₁⁽⁰⁾配合物，可以可逆地聚集成活性 Pd _n簇和纳米颗粒形成可相互转换的 Pd _n⁽⁰⁾混合物各种核的活性物质（即，“ n”）。涉及 Ni(0) 配合物的镍体系通常需要特殊的强还原剂；它们对空气和其他氧化剂的失活更敏感，因此，在相同反应中，它们通常在比钯系统更高的催化剂负载下运行。低价活性 Pd 物种的易于活化和相对较高的稳定性为钯催化提供了高稳定性和多功能性，而各种 Ni 氧化态可以实现更多样化和不常见的反应性，尽管在镍催化的活化和稳定方面需要付出更大的努力系统。作为讨论的重点，我们可能会注意到 Pd 催化系统可能很容易形成具有不同核度但氧化态相似的“粒子混合物”（Pd ₁，Pd _n，Pd NPs），而镍在不同氧化态下可能表现为“物种混合物”，但在稳定核中变化较小。毫无疑问，不仅需要开发改进的高效催化剂，而且需要了解 Pd 和 Ni 催化系统的机理，这一点比以往任何时候都更加强烈。

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Nickel and Palladium Catalysis: Stronger Demand than Ever

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 Pd₁⁽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 (Pd₁, 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.

更新日期：2022-01-21

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