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 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 (PNMR)-P-31 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 (PNMR)-P-31 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.