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.