Four new charged iridium(III) 1,2,3,4,5-pentamethylcyclopentadienyl (Cp*) complexes, 1–4, of the type [Cp*Ir(L1–4)(PTA)](PF6) (where L1–4 = functionalized β-ketoiminate ligands and PTA = 1,3,5-triaza-7-phosphaadamantane), have been successfully synthesized and characterized. Single crystal X-ray crystallographic data have been obtained for all compounds and confirm a typical pseudo-octahedral half-sandwich geometry. Cytotoxicity values have been determined against a range of cancerous and noncancerous cell lines and highlight high cytotoxicity and selectivity toward breast cancers. Among these compounds, the unfunctionalized β-ketoiminate Ir(III) complex (1) emerged as the most promising candidate, demonstrating activity that was comparable to or exceeded that of cisplatin, especially after 24 h against the triple-negative MDA-MB-231 cell line. Morphological and molecular analyses confirmed that 1 triggers apoptotic cell death, involving caspase activation and PARP cleavage, which is consistent with its DNA-damaging characteristics, highlighting the future anticancer potential of compound 1.