Formation of Iridium(III) and Rhodium(III) Amine, Imine, and Amido Complexes Based on Pyridine–Amine Ligands: Structural Diversity Arising from Reaction Conditions, Substituent Variation, and Metal Centers

Abstract

Herein, we present the different coordination modes of half-sandwich iridium(III) and rhodium(III) complexes based on pyridine−amine ligands. The pyridyl−amine iridium(III) and rhodium(III) complexes, the corresponding oxidation pyridyl− imine products, and 16-electron pyridyl−amido complexes can be obtained through the change in reaction conditions (nitrogen/ adventitious oxygen atmosphere, reaction time, and solvents) and structural variations in the metal and ligand. Overall, the reaction of pyridine−amine ligands with [(η 5 -C 5 (CH 3 ) 5 )MCl 2 ] 2 (M = Ir or Rh) in the presence of adventitious oxygen afforded the oxidized pyridyl−imine complexes. The possible mechanism for the oxidation of iridium(III) and rhodium(III) amine complexes was confirmed by the detection of the byproduct hydrogen peroxide. Moreover, the formation of pyridyl−amine complexes was favored when nonpolar solvent CH 2 Cl 2 was used instead of CH 3 OH. The rarely reported complex with [(η 5 -Cp*)IrCl 3 ] anions can also be obtained without the addition of NH 4 PF 6 . The introduction of the sterically bulky i-Bu group on the bridge carbon of the ligand led to the formation of stable 16-electron pyridyl−amido complexes. The pyridyl−amine iridium(III) and rhodium(III) complexes were also synthesized under a N 2 atmosphere, and no H 2 O 2 was detected in the whole process. In particular, the aqueous solution stability and in vitro cytotoxicity toward A549 and HeLa human cancer cells of these complexes were also evaluated. No obvious selectivity was observed for cancer cells versus normal cells with these complexes. Notably, the represented complex 5a can promote an increase in the reactive oxygen species level and induce cell death via apoptosis.

Half-Sandwich Iridium(III), Rhodium(III), and Ruthenium(II) Complexes Chelating Hybrid sp2-N/sp3-N Donor Ligands to Achieve Improved Anticancer Selectivity

“…This weakly photoluminescent behavior was also observed in the previously reported half-sandwich Ir(III), Rh(III), and Ru(II) complexes. 40,44,55 However, the photoluminescent characteristic of these complexes rendered it possible to explore MoAs by bioimaging.…”

“…However, the coordination of sp 2 -N/sp 3 -N pyridyl-amine ligands activated their oxidation to the corresponding pyridyl-imine Ir(III) and Rh(III) complexes when the small amount of molecular oxygen was not rigorously excluded from the reaction medium (Scheme 1, VI and VII). 40 The easily oxidized nature of these unstable pyridyl-amine complexes makes it difficult to evaluate their anticancer activities. Along this line, we herein synthesized a new series of half-sandwich imine−amine (sp 2 -N/sp 3 -N) Ir(III), Rh(III), and Ru(II) complexes with functionalized BIAN ligands (Scheme 1).…”

“…We further became interested in expanding the investigation to hybrid sp 2 -N/sp 3 -N amine-metal (C-(R)­HN → Mt) complexes. However, the coordination of sp 2 -N/sp 3 -N pyridyl-amine ligands activated their oxidation to the corresponding pyridyl-imine Ir­(III) and Rh­(III) complexes when the small amount of molecular oxygen was not rigorously excluded from the reaction medium (Scheme , VI and VII ) . The easily oxidized nature of these unstable pyridyl-amine complexes makes it difficult to evaluate their anticancer activities.…”

Exploring the antioxidant, antimicrobial, cytotoxic and biothermodynamic properties of novel morpholine derivative bioactive Mn(ii), Co(ii) and Ni(ii) complexes – combined experimental and theoretical measurements towards DNA/BSA/SARS-CoV-2 3CLPro

“…Complexes (1-3) are found in either the singlet or doublet ground states, depending on the electronic structure of the central metal. Note that the electronic configurations of metal(II) complexes (1-3) are 3d 5 (1), 3d 7 (2), and 3d 8 (3), respectively, which should exhibit paramagnetic characters due to a weak field and a high-spin ligand. In particular, complex (3) has two unpaired electrons in the e g high energy level orbital and six electrons in the t 2g low energy orbital, in accordance with crystal field theory.…”

“…4 Platinumbased drugs are currently available for the treatment of cancer chemotherapy and account for nearly 50% of cancer therapeutic medications globally, but the majority of these unfortunately have a lot of negative side effects, being extremely toxic and drug resistant, and they lose selectivity in chemotherapy due to the formation of covalent interactions. 5,6 To overcome these drawbacks, transition metal complexes other than platinum have attracted particular attention due to their diverse oxidation states and lower toxicity. 7,8 Moreover, free radicals play a role in several aspects of the body's normal oxygen metabolism, including vasodilation (blood vessel dilatation), the immune response, cell differentiation, and electron transfer in the mitochondrial respiratory chain.…”