A naphthalene-based heterobimetallic triazolylidene Ir/Pd complex: regioselective to regiospecific C-H activation, tandem catalysis and a copper-free Sonogashira reaction

Heterobimetallic complexes featuring mesoionic carbene (MIC) donor ligands are gaining enormous popularity in tandem catalysis owing to the combined action of two different metal centers during catalysis. A rare version of the heterobimetallic Pd II /Ir III complex possessing a cyclometalated mesoionic carbene (MIC) ligand is presented along with the analogous homodinuclear Pd II complex. A sterically controlled regiospecific cyclometalation towards the formation of a six-membered ring complex over a five-membered ring complex has been performed using a naphthalene-based bis-MIC ligand platform. The interplay between regioselective vs. regiospecific C-H bond activation for the synthesis of cyclometalated Ir III complexes has also been demonstrated using the corresponding naphthyl-derived mono-imidazolylidene ligand. Both homodinuclear Pd II and heterobimetallic Pd II /Ir III complexes have been characterized using standard spectroscopic techniques including 1 H, 13 C{ 1 H}, 2D correlation NMR spectroscopy and ESI mass spectrometry. The structure of the cyclometalated heterobimetallic complex has been established by single crystal XRD. The heterobimetallic complex has been employed as a pre-catalyst in the tandem Suzuki-Miyaura/transfer hydrogenation reaction and the homobimetallic Pd II complex has been successfully employed as a catalyst in both the Sonogashira coupling and α-arylation of 1-methyl-2-oxindole. A rare version of naphthalene-based heterobimetallic PdII/IrIII complex possessing cyclometalated mesoionic bis-carbene (MIC) ligand is presented. The complex has been employed as pre-catalyst in the tandem Suzuki−Miyaura/transfer hydrogenation reaction.