Heterobimetallic Carbene Complexes Bearing Cyclometalated IrIII/RhIII and Mixed NHC∧ Py/PPh3 Coordinated PdII Centers: Structures and Tandem Catalysis

• Published in: European journal of inorganic chemistry Vol. 2021; no. 12; pp. 1104 - 1110
• Main Authors: Majumder, Adhir, Nath Saha, Tarak, Majumder, Niladri, Naskar, Rajat, Pal, Kuntal, Maity, Ramananda
• Format: Journal Article
• Language: English
• Published: Weinheim Wiley Subscription Services, Inc 26.03.2021
• Subjects: Carbene ligands; Cascade chemical reactions; Catalysis; Coordination compounds; Crystallography; Heterobimetallic complexes; Inorganic chemistry; Ligands; Organometallic compounds; Selectivity; Structure elucidation; Tandem catalysis; Transfer hydrogenation
• ISSN: 1434-1948; 1099-0682
• DOI: 10.1002/ejic.202001080

Heterobimetallic complexes bearing NHC donor ligands are gaining immense popularity in organometallic chemistry and tandem catalysis. It is known that the NHC reacts with PdII in the presence of pyridine to yield PEPPSI type complexes and the NHC ligands having ortho‐C−H proton easily orthometalate to IrIII or RhIII centers. Combining these two methodologies in a stepwise fashion, we present here a series of heterobimetallic IrIII−PdII and RhIII−PdII complexes from a dicarbene donor ligand featuring cyclometalated IrIII or RhIII and mixed NHC∧Py /PPh3 coordinated PdII centers. All the heterobimetallic complexes have been structurally characterized by X‐ray crystallographic analysis. The heterobimetallic complexes featuring mixed NHC∧PPh3 coordinated PdII centers show better activity in tandem Suzuki‐Miyaura/transfer hydrogenation reactions compared to both, the heterobimetallic complexes possessing PEPPSI type PdIIcenters, and the equimolar mixture of their mononuclear PdII and RhIII or IrIII counterparts. The heterobimetallic complex featuring cyclometalated IrIII and mixed NHC∧PPh3 coordinated PdII center shows excellent selectivity for 4‐biphenylmethanol (isolated yield: 92 %) in tandem catalysis. A series of heterobimetallic MIII−PdII (M=Rh, Ir) complexes from a dicarbene donor ligand featuring cyclometalated MIII and mixed NHC∧Py /PPh3 coordinated PdII is presented. The IrIII−PdII complex featuring mixed NHC∧PPh3 donor ligands at the PdII center was the best catalyst and provided an excellent yield of 4‐biphenylmethanol (isolated yield: 92 %) in the tandem catalysis.