A Novel Organometallic Re I Complex with Favourable Properties for Bioimaging and Applicability in Solid‐Phase Peptide Synthesis

Organometallic complexes possess great potential for imaging applications in biology, due to their kinetic stability and often favourable intrinsic properties. In this work we present a new class of Re I ‐tricarbonyl complexes with a substituted bis(phenanthridinylmethyl)amine (bpm) ligand. The complex Re(CO) 3 (R‐bpm) could be conveniently prepared by microwave synthesis from [Re(CO) 3 (H 2 O) 3 ]Br and a suitably substituted bis(phenanthridinylmethyl)amine (R‐bpm). Complex 5 , with R=CH 2 ‐CO 2 ‐CH 3 , was characterized by a single‐crystal X‐ray structure. Complex 6 (R=CH 2 ‐C 6 H 4 ‐CO 2 H) was used in solid‐phase peptide synthesis (SPPS) to label the neurotensin(8–13) (NT) fragment N‐terminally. The complexes show luminescence emission with large Stokes shifts ( λ ex =350 nm, λ em =570 nm). Cellular uptake and intracellular localization studies in several cell lines demonstrate the utility of the new Re(CO) 3 (R‐bpm) complexes for fluorescence imaging and reveal significant differences between the simple methyl ester 5 and the NT bioconjugate 7 .