An evaluation of the in vitro cytotoxicity of nine electron‐deficient half‐sandwich metal complexes towards two colorectal cancer cell lines (HCT116 p53+/+, HCT116 p53−/−) and one normal prostate cell line (PNT2) is presented herein. Three complexes were found to be equally cytotoxic towards both colorectal cancer cell lines, suggesting a p53‐independent mechanism of action. These complexes are 12 to 34× more potent than cisplatin against HCT116 p53+/+ and HCT116 p53−/− cells. Furthermore, they were found to exhibit little or no cytotoxicity towards PNT2 normal cells, with selectivity ratios greater than 50. To gain an insight into the potential mechanisms of action of the most active compounds, their effects on the expression levels of a panel of genes were measured using qRT‐PCR against treated HCT116 p53+/+ and HCT116 p53−/− cells, and cell‐cycle analysis was carried out.