Heterobimetallic Carbene Complexes Bearing Cyclometalated Ir^III/Rh^III and Mixed NHCPy/PPh₃ Coordinated Pd^II Centers: Structures and Tandem Catalysis

Abstract

Abstract Heterobimetallic complexes bearing NHC donor ligands are gaining immense popularity in organometallic chemistry and tandem catalysis. It is known that the NHC reacts with Pd II in the presence of pyridine to yield PEPPSI type complexes and the NHC ligands having ortho‐C−H proton easily orthometalate to Ir III or Rh III centers. Combining these two methodologies in a stepwise fashion, we present here a series of heterobimetallic Ir III −Pd II and Rh III −Pd II complexes from a dicarbene donor ligand featuring cyclometalated Ir III or Rh III and mixed /PPh 3 coordinated Pd II centers. All the heterobimetallic complexes have been structurally characterized by X‐ray crystallographic analysis. The heterobimetallic complexes featuring mixed coordinated Pd II centers show better activity in tandem Suzuki‐Miyaura/transfer hydrogenation reactions compared to both, the heterobimetallic complexes possessing PEPPSI type Pd II centers, and the equimolar mixture of their mononuclear Pd II and Rh III or Ir III counterparts. The heterobimetallic complex featuring cyclometalated Ir III and mixed coordinated Pd II center shows excellent selectivity for 4‐biphenylmethanol (isolated yield: 92 %) in tandem catalysis.