Iridium(III) Complexes containing 1,10-Phenanthroline and Derivatives – Synthetic, Stereochemical and Structural Studies, and their Antimicrobial Activity.

A convenient synthetic strategy is reported for the series of complexes [Ir(pp)₃]³⁺ (where pp = phen, Me₂phen and Me₄phen) through the intermediacy of the appropriate [Ir(pp)2(CF3SO3)2]+ species. In the case of [Ir(phen)3]3+, the cation was resolved into its enantiomeric forms, for which the absolute configurations were determined by X-ray diffraction. The availability for the first time of the CD spectra allowed comparison with computed CD spectra. Measurement of the antimicrobial activity of the [Ir(pp)₃]³⁺ species {and the [Ir(pp)₂X₂]+ (X = Cl^–, CF₃SO₃^–) precursors involved in their synthesis}, as well as cell uptake studies with the four bacterial strains S. aureus, methicillin-resistant S. aureus (MRSA), E. coli, and P. aeruginosa, indicated that they showed little activity compared with their Ru(II) analogues. The results suggest that it is unfavourable for an individual metal centre with a 3+ charge to pass across the bacterial cell membrane.