New silver, rhodium and iridium complexes with anthracene-functionalized N-heterocyclic carbene ligands: Crystal structures, cytotoxicity and fluorescence studies

In the present study, we have synthesized anthracene-functionalized metal complexes to investigate their cytotoxicity and photophysical properties. In this context, firstly, an Ag–NHC (NHC = N-heterocyclic carbene) complex (2a) have been synthesized by the interaction of Ag2O and N-(2-methylbenzyl)-N-((anthracen-9-yl)methyl)benzimidazolium chloride (1a). Corresponding Rh– (3a) and Ir–NHC (4a) complexes have also been synthesized by the transmetalation reaction between 2a and corresponding metal compounds. Additionally, for comparison purposes, an ether-functionalized Ag–NHC complex (2b) with N-(methoxyethyl)-N-((anthracene-9-yl)methyl)benzimidazole-2-ylidene ligand, and [AgL2]NO3 type complex (2c) with a N-coordinated N-((anthracen-9-yl)methyl)benzimidazole ligand have been synthesized. All complexes have been characterized by the combination of NMR and mass spectroscopic techniques, and elemental analyses. Moreover, solid state structures of 2a, 2b and 4a have been determined by the single crystal X-ray diffraction analysis. Cytotoxic potentials of all compounds have been tested against human lung adenocarcinoma alveolar basal epithelial cell line (A549) using the MTT assay, and all complexes performed strong anti-proliferative activity. Stability studies have disclosed that only 1a and 2c are able to retain their structure in the culture medium (DMEM) that biological assays were carried out. Photophysical measurements revealed that all compounds have similar emission bands because of the conjugation of anthracene group. Finally, 1a and 2c have been visualized by fluorescence confocal microscopy to investigate cellular uptake and subcellular distribution of the complexes, and the findings indicated that both compounds dispersed along the cell membranes nuclear regions