Synthesis and Characterization of RhIII–MII (M = Pt, Pd) Heterobimetallic Complexes Based on a Bisphosphine Ligand: Tandem Reactions Using Ethanol

1,1-Bis­(diphenylphosphino)­methane (dppm) was used as a linker ligand for the preparation of a series of heterobimetallic RhIII–PtII and RhIII–PdII complexes. These complexes were characterized by means of several analytical and spectroscopic methods. The catalytic activities of these heterobimetallic complexes were carried out in three different tandem reactions: namely, transfer hydrogenation (TH)/dehalogenation (DH), TH/Suzuki–Miyaura coupling, and coupling of benzylic alcohols with nitrobenzenes for Schiff base construction. Ethanol was used as both the solvent and an inexpensive TH reagent, where a broad substrate scope was demonstrated for these tandem reactions. All reactions proceeded smoothly in air at 80–90 °C. The RhIII–PdII complex showed superior catalytic performance in comparison to the RhIII–PtII complexes, its monometallic counterparts, and mixtures of monometallic (RhIII + PdII) complexes. The result demonstrates a cooperative effect between the Rh and Pd metal centers. A mechanism for the catalytic tandem reactions was investigated. It was found that alcohol medium and base are essential.