Novel metal-coordinated 1,10-phenanthroline ligands functionalized with a lactam or imide

•Novel metal-coordinated 1,10-phenanthrolino[5,6-c]-1,5-dihydropyrrol-2-one ligand.•Novel metal-coordinated 1,10-phenanthroline-5,6-carboximide ligand.•Hydrogen bond donor/acceptor motifs useful for biomolecular recognition.•Cyclometalated iridium complexes with pH-dependent luminescence.

Metal-coordinated “γ-lactam-capped” and “imide-capped” 1,10-phenanthroline ligands are reported. Whereas the imide-functionalized ligand 1,10-phenanthroline-5,6-carboximide could not be obtained as a free ligand, probably due to its extremely low solubility, we developed a protocol to first introduce the more soluble 1,10-phenanthrolino[5,6-c]pyrrole in the ligand sphere of cyclometalated iridium(III) complexes, followed by the oxidation of the pyrrole moiety to a maleimide utilizing a peroxybenzoic acid. The hydrogen bond donor–acceptor properties of the new ligands should make them suitable building blocks for the design of metal-based protein binders. Furthermore, we unexpectedly found that bis-cyclometalated iridium(III) complexes coordinated to 1,10-phenanthroline-5,6-carboximide display luminescence properties that are dependent on the protonation state of the maleimide NH group. It can be envisioned to exploit this behavior for the real-time monitoring of hydrogen bonding interactions in biological systems.

Graphical abstractThe synthesis and metal coordination of novel “γ-lactam-capped” and “imide-capped” 1,10-phenanthroline ligands is reported including the pH-dependent luminescence of cyclometalated iridium(III) complexes bearing 1,10-phenanthroline-5,6-carboximide.Figure optionsDownload full-size imageDownload as PowerPoint slide