Evidence of Hybrid Homogeneous–Heterogeneous Catalysis in a Pt/Au Heterobimetallic System

Abstract

We report here our efforts towards understanding the catalytic species involved in a novel Pt/Au heterobimetallic system capable of efficiently catalysing the tandem cyclisation/C−X coupling reaction of heteroarylallenes with C‐ and N‐based nucleophiles. Our results confirm that homogeneous Au‐catalysis is involved at the beginning of the reaction to generate an intermediate that enters the second catalytic cycle in which hybrid homogeneous–heterogeneous catalysis by [Pt–Au] clusters could be responsible for the high efficiency. In this part of the cycle, [Pt–AuPPh3] homogeneous clusters (identified by 31P NMR analysis) seem to be aided by Pt–Au particles in the heterogeneous phase (supported by Hg poisoning, filtration experiments and characterisation of the possible catalytic species by several techniques, such us 31P NMR spectroscopy, inductively coupled plasma mass spectrometry, SEM and dynamic light scattering experiments). Here, full Pt‐to‐Au transmetallation was not observed contrary to the results with other bimetallic systems. Although a few examples of hybrid homogeneous–heterogeneous catalysis in monometallic systems exist, to the best of our knowledge, this is the first example of hybrid homogeneous–heterogeneous catalysis in systems involving two different metals.

Platinum and Gold Catalysis: à la Carte Hydroamination of Terminal Activated Allenes with Azoles

“…In the context of allene chemistry, Au–Pd dual catalysis has been reported in the reaction of allenoates to form butenolides . We have recently reported a dual Au–Pt strategy for the reaction of heteroarylallenes in the reaction with heteroaromatic nucleophiles, showing unprecedented reactivity not observed previously with single catalysis strategies …”

When Indoles Meet Allene and its Derivatives

“…Detailed investigations into this transformation suggested that the more efficient bimetallic strategy vs. the single catalyst methodology was due to synergic cooperation between soluble gold-platinum clusters in equilibrium with heterogeneous goldplatinum particles generated in situ, reporting, therefore, the first example of hybrid homo-heterogeneous catalysis in a bimetallic system. [75] Tandem reactions involving untethered indoles and allenes are increasingly appearing in the literature and most of the examples are from the last 3 years. In most of them, the intermolecular reaction occurs first to give intermediates that undergo intramolecular processes.…”

“…Detailed investigations into this transformation suggested that the more efficient bimetallic strategy vs. the single catalyst methodology was due to synergic cooperation between soluble gold‐platinum clusters in equilibrium with heterogeneous gold‐platinum particles generated in situ, reporting, therefore, the first example of hybrid homo‐heterogeneous catalysis in a bimetallic system. [ 75 ]…”

Luminescent Heterobimetallic PtII–AuI Complexes Bearing N-Heterocyclic Carbenes (NHCs) as Potent Anticancer Agents

“…An upward trend in the publication of binuclear complexes has been visible over the past decade. Meanwhile, investigations of heterobimetallic Pt–Au systems show a leap forward in different categories, including structural, − photoluminescence, − catalysis, , and therapeutic. Although heterobimetallic Pt–Au systems are still in the early stages of development, their reasonable biological features make them a viable and highly potent class of cancer chemotherapeutic agents.…”