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

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 = 185/187Re or 188Re). The strategy includes the facile preparation of these N2O ligands bearing various functionalized arms (carboxylate, terminal alkyne, aromatic amine). The reaction of commercial [Re(CO)5Cl] {or a freshly prepared [Re(OH2)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 [188Re(CO)3(5)] and [188Re(CO)3(11–H)] were also prepared, in acceptable to excellent yields, by the reaction of 5 or 11 with the fac‐[188Re(OH2)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 ReI core combined with the ease of their derivatization make this chelating system promising for the conception of target‐specific radiopharmaceuticals for therapeutic purposes. Novel tricarbonylrhenium complexes of the general formula [Re(CO)3(L)], in which LH is an N2O tridentate click ligand, have been prepared and fully characterized, including by X‐ray crystallography and DFT calculations. The analogous [188Re(CO)3(L)] complexes were also investigated and their structures established by HPLC. This study shows the great potential of tripodal click scaffolds for 188ReI.