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Emmanuel Serrano-Díez1, Alejandra Pita-Milleiro1, Jesús Rangel-García1

  • 1Instituto de Investigaciones Químicas (IIQ), Departamento de Química Inorgánica and Centro de Innovación en Química Avanzada (ORFEO-CINQA), Universidad de Sevilla and Consejo Superior de Investigaciones Científicas (CSIC). Avenida Américo Vespucio 49, 41092 Sevilla, Spain.

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Gold complexes reversibly inhibit iridium catalysts, enhancing selectivity in alkyne hydrogenation. This bimetallic inhibition strategy improves olefin formation by preventing overreduction, offering a new approach to catalysis.

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Area of Science:

  • Organometallic Chemistry
  • Catalysis
  • Homogeneous Catalysis

Background:

  • Bimetallic complexes often enhance catalytic activity compared to monometallic systems.
  • The concept of using a second metal to intentionally decrease catalytic activity (inhibition) is less explored.
  • The iridium Vaska complex is an iconic catalyst for hydrogenation reactions.

Purpose of the Study:

  • To explore reversible bimetallic inhibition as a strategy to control catalytic activity and selectivity.
  • To synthesize and characterize electrophilic gold complexes as potential inhibitors for an iridium-based catalyst.
  • To investigate the mechanism of inhibition and its effect on alkyne semihydrogenation.

Main Methods:

  • Synthesis of nine electrophilic gold complexes (Au(PR3)(NTf2)).
  • Characterization of heterobimetallic Ir-Au complexes formed in situ.
  • Application of gold complexes as inhibitors in the semihydrogenation of terminal and internal alkynes catalyzed by the Vaska complex.
  • Computational studies to elucidate the mechanism of inhibition and catalytic pathways.

Main Results:

  • Electrophilic gold complexes, except for sterically hindered ones, form bimetallic Ir-Au complexes with dative Ir → Au bonds.
  • These bimetallic structures exhibit a strong preference for olefin formation in alkyne hydrogenation, minimizing overreduction.
  • Computational studies confirmed the reversible formation of heterobimetallic structures and gold's role in passivating iridium.
  • The inhibition strategy significantly enhanced selectivity towards desired olefin products compared to the uninhibited iridium catalyst.

Conclusions:

  • Reversible bimetallic inhibition using gold complexes is an effective strategy to control selectivity in iridium-catalyzed alkyne hydrogenation.
  • The formation of heterobimetallic Ir-Au species modulates the catalytic activity of the iridium center, leading to enhanced olefin selectivity.
  • This work presents a novel approach to catalyst design by leveraging inhibitory interactions for improved catalytic performance.