A series of histidine derived Au(I) bis‐NHC complexes bearing different ester, amide and carboxylic acid functionalities as well as wingtip substituents is synthesized and characterized. The stability in aqueous media, in vitro cytotoxicity in a set of cancer cell lines (MCF7, PC3 and A2780/A2780cisR) along with the cellular uptake are evaluated. Stability tests suggest hydrolysis of the ester within 8 h, which might lead to deactivation. Furthermore, the bis‐NHC system shows a sufficient stability against cysteine and the thiol containing peptide GSH. The benzyl ester and amide show the highest activity comparable to the benchmark compound cisplatin, with the ester only displaying a slightly lower cytotoxicity than the amide. A cellular uptake study revealed that the benzyl ester and the amide could have different intracellular distribution profiles but both complexes induce perturbations of the cellular physiological processes. The simple modifiability and high stability of the complexes provides a promising system for upcoming post modifications to enable targeted cancer therapy.

With the aim to design new water-soluble organometallic Ru(II) complexes acting as anticancer agents catalysing transfer hydrogenation (TH) reactions with biomolecules, we have synthesized four Ru(II) monocarbonyl complexes (1-4) featuring the 1,4-bis(diphenylphosphino)butane (dppb) ligand and different bidentate nitrogen (N^N) ligands, of general formula [Ru(OAc)CO(dppb)(N^N)]n (n = +1, 0; OAc = acetate). The compounds have been characterised by different methods, including 1H and 31P NMR spectroscopy, electrochemistry as well as single crystals X-ray diffraction in the case of 1 and 4. The compounds have also been studied for their hydrolysis in aqueous environment, and for the catalytic regioselective reduction of NAD+ to 1,4-NADH in aqueous solution with sodium formate as hydride source. Moreover, the stoichiometric and catalytic oxidation of 1,4-NADH have also been investigated by UV-Visible spectrophotometry and NMR spectroscopy. Overall, initial structure-activity relationships could be inferred which point towards the influence of the extension of the aromatic N^N ligand in the cationic complexes 1-3 on the TH in both reduction/oxidation processes. The neutral complex 4, featuring a picolinamidate N^N ligand, stands out as the most active catalyst for the reduction of NAD+, while being completely inactive towards NADH oxidation. The compound can also convert pyruvate into lactate in the presence of formate, albeit with scarce efficiency. In any case, for all compounds, Ru(II) hydride intermediates could be observed and even isolated in the case of complexes 1-3. Together, insight from the kinetic and electrochemical characterization suggests that, in the case of Ru(II) complexes 1-3, catalytic NADH oxidation sees the H-transfer from 1,4-NADH as the rate limiting step, whereas for NAD+ hydrogenation with formate as the H-donor, the rate limiting step is the transfer of the ruthenium hydride to the NAD+ substrate. The latter is further modulated by the presence of di-cationic aquo- or mono-cationic hydroxo-species of complexes 1-3. Instead, compound 4, stable with respect to hydrolysis in aqueous solution, appears to operate via a different mechanism. Finally, the anticancer activity and ability to form reactive oxygen species (ROS) of complexes 1-3 have been studied in cancerous and non-tumorigenic cells in vitro. Noteworthy, the conversion of aldehydes to alcohols could be achieved by the three Ru(II) catalysts in living cells, as assessed by fluorescence microscopy. Furthermore, the formation of Ru(II) hydride intermediate upon treatment of cancer cell extracts with complex 3 has been detected by 1H NMR spectroscopy. Overall, this study paves the way to the application of non-arene based organometallic complexes as TH catalysts in biological environment.