Rhenium Complexes Based on an N₂O Tridentate Click Scaffold: From Synthesis, Structural and Theoretical Characterization to a Radiolabelling Study

Abstract

A general synthetic approach to a novel range of semirigid bifunctional chelating agents (BCAs) that include an aromatic ring and a triazolyl moiety in the chelating unit has been investigated for the fac ‐[M(CO) 3 ] + core (M = 185/187 Re or 188 Re). The strategy includes the facile preparation of these N 2 O ligands bearing various functionalized arms (carboxylate, terminal alkyne, aromatic amine). The reaction of commercial [Re(CO) 5 Cl] {or a freshly prepared [Re(OH 2 ) 3 (CO) 3 ] + precursor} with our BCAs in methanol led to the formation of stable neutral tricarbonylrhenium complexes of general formula [Re(CO) 3 (L)] (LH = 5 , 10 , 11 ) in high yields. These compounds were characterized by IR and NMR spectroscopy, mass spectrometry, electrochemistry, and X‐ray crystallography for [Re(CO) 3 ( 5 –H )] and [Re(CO) 3 ( 11 –H )] as well as by DFT calculations. The analogous rhenium‐188 complexes [ 188 Re(CO) 3 ( 5 )] and [ 188 Re(CO) 3 ( 11 –H )] were also prepared, in acceptable to excellent yields, by the reaction of 5 or 11 with the fac ‐[ 188 Re(OH 2 ) 3 (CO) 3 ] + precursor in methanol at 80 °C. The structural identities of the radioactive complexes were assessed by HPLC studies. The good affinity of these click ligands for the Re I core combined with the ease of their derivatization make this chelating system promising for the conception of target‐specific radiopharmaceuticals for therapeutic purposes.