Heterobimetallic Catalysis: Platinum‐Gold‐Catalyzed Tandem Cyclization/C−X Coupling Reaction of (Hetero)Arylallenes with Nucleophiles

Heterobimetallic catalysis offers new opportunities for reactivity and selectivity but still presents challenges, and only a few metal combinations have been explored so far. Reported here is a Pt‐Au heterobimetallic catalyst system for the synthesis of a family of multi‐heteroaromatic structures through tandem cyclization/C−X coupling reaction. Au‐catalyzed 6‐endo‐cyclization takes place as the first fast step. Pt‐Au clusters are proposed to be responsible for the increased reactivity in the second step, that is, the intermolecular nucleophilic addition which occurs through an outer‐sphere mechanism by hybrid homogeneous‐heterogeneous catalysis

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

We report here our efforts towards understanding the catalytic species involved in a novel Pt/Au heterobimetallic system capable of efficiently catalyse the tandem cyclisation/C-X coupling reaction of heteroarylallenes with C- and N-based nucleophiles. Our evidence confirm that homogeneous Au-catalysis is involved at the beginning of the reaction to generate an intermediate that enters the second catalytic cycle where 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) seem to be aided by Pt-Au particles in the heterogeneous phase (supported by Hg poisoning and filtration experiments, and characterization of the possible catalytic species by several techniques, e.g. 31P NMR, ICP-MS, SEM, DLS), with full Pt- to-Au transmetallation not being observed in contrast with other reported bimetallic systems. There are a few examples of hybrid homogeneous-heterogeneous catalysis in monometallic systems, but to the best of our knowledge this is the first example of hybrid homo- heterogeneous catalysis in systems involving two different metals