Transition metal complexes with NHC based pincer ligands–synthesis, characterization, and reactivity

Abstract

NHC ligand precursors, 2,6-Bis(1-methylimidazolium pyridine)dibromide (CNCMe·2HBr), 2,6-Bis(1-isopropylimidazoliumpyridine)dibromide (CNCi-Pr·2HBr) were prepared by following literature procedures. Different metal precursors were synthesized by using a protocols recently developed in our group, starting from RuCl3·3H2O. Ru(II) complexes, [Ru(CNC)i-Pr(PPh3)2Cl]PF6 (1), [Ru(CNC)i-Pr(DMSO)2Cl]PF6 (2), [Ru(CNC)i-Pr(COD)Cl]PF6 (3), [Ru(CNC)i-Pr(PPh3)(CO)Cl]PF6 (4), [Ru(CNC)i-Pr(PPh3)2H]PF6 (5), and [Ru(CNC)Me(PPh3)2H]PF6 (6), [Ru(CNC)i-Pr(PPh3)2(N3)]Cl (7) have been synthesized by reaction of NHC ligand precursors and other metal precursors under thermal condition. All the synthesized ligands and complexes have been characterized by mass spectrometry and multinuclear NMR (1H and 31P NMR) and FTIR spectroscopic techniques. The molecular structure of complexes 1, 2, and 5 was confirmed by single-crystal X-ray diffraction technique. The crystal structures reveal that the Ru (II) center is coordinated with one tridentate NHC donor ligands and other monodentate ligands forming a distorted octahedron.