Cytotoxic Activities of Bis‐cyclometalated Iridium(III) Complexes Containing Chloro‐substituted κ²N‐terpyridines

Abstract

Dedicated to Professor Wolfgang Beck on the Occasion of his 90th Birthday.The synthesis and characterization of two new bis-cyclometalated compounds [Ir(ptpy) 2 (k 2 N-terpy-C 6 H 4 Cl-p)]PF 6 [terpy-C 6 H 4 Cl-p = 4'-(4-chlorophenyl)-2,2':6',2''-terpyridine, (1)], and [Ir-(ptpy) 2); ptpy = 2-(p-tolyl)pyridinato)] are described. The molecular structures of compounds 1 and 2 in the crystal were determined by single-crystal X-ray diffraction. 1 crystallized from dichloromethane/methanol/iso-hexane in the monoclinic space group P2/ n and 2 from the same mixture of solvents in the triclinic space group P À 1. Photophysical investigations on 1 and 2 revealed broad unstructured luminescence in the red spectral region with the emission maxima in dichloromethane at 620 and 630 nm respectively. To explore cytotoxic properties of compounds 1 and 2, a colorimetric assay (MTT assay) against prominent cancer cell lines, MCF-7 and HT-29, was performed. The determined IC 50 values are in the low micromolar range (2-3 μM). In comparison to cisplatin, the tested complexes 1 and 2 exhibit up to > 20-fold (MCF-7) and > 40-fold (HT-29) increase in biological activity.

Cytotoxic Activities of Bis‐cyclometalated M(III) Complexes (M=Rh, Ir) Containing 5‐substituted 1,10‐Phenanthroline or 4,4’‐substituted 2,2’‐Bipyridine Ligands

“…In comparing the phenanthroline and bipyridine ligands, a slight difference is noticeable. The compounds with phenanthroline-based ligands (1-4) seem to have an overall higher cytotoxicity than those with substituted bipyridine ligands (5)(6)(7)(8). Considering the different substituents of phenanthroline, either 5-chloro or 5methyl, the 5-chloro-substituted phenanthroline systems (1, 2) seem to be marginal more active, particularly in MCF-7 cells.…”

“…[13] All in all, the inspection of the IrÀ N and IrÀ C bond parameters including the corresponding bond angles of compounds 5, 6, and 8 afforded a very good accordance with the usually observed ones in closely related compounds reported by us. [7]…”

“…[6] In the course of related investigations we have a current interest in studies of the cytotoxic activity of bis-cyclometalated iridium(III) compounds towards some human cancer cell lines by examining the substituent influences in the sphere of the ancillary ligands. [7] Thus, we investigated the cytotoxic activities of some derivatives containing modified phenanthroline, and related bipyridine ligands respectively. [8,9] To continue our efforts in this field we describe herein the synthesis and the characterization of eight new bis-cyclometalated M(III) complexes (M = Rh, Ir) as well as the evaluation of the cytotoxic activities of these compounds.…”