Design, Synthesis, and Reactivity of Multidentate Ligands with Rhenium(I) and Rhenium(V) Cores: Design, Synthesis, and Reactivity of Multidentate Ligands with Rhenium(I) and Rhenium(V) Cores

Synthetic pathways to a range of potentially N3O tetradentate ligands, designed to coordinate rhenium cores as well as their coordination behaviours towards different rhenium cores (oxidation states +I and +V) are investigated. Two functionalized N-((1-(4-R)-1H-1,2,3-triazol-4-yl)methyl)-2-(pyridin-2-ylmethoxy)aniline derivatives L1H (R = methyl acetate) and L2H (R = 4-nitrophenyl) act exclusively as bidentate ligands and lead to the formation of mononuclear tricarbonylrhenium(I) complexes of general formula [(LH)Re(CO)3Cl] with L = L1 or L2. Both complexes are characterized by 1H and 13C NMR, FT-IR spectroscopy, electrospray ionization mass spectrometry and in the case of [(L2H)Re(CO)3Cl] single crystal X-ray diffraction study. The rhenium is coordinated by the three carbonyl groups, the chlorine and the two nitrogens of the triazole and the nitrogen of the aniline ring of the ligand, respectively. Theoretical study shows complex [(L2H)Re(CO)3Cl] is the most stable structural isomer. In addition, the oxorhenium(V) complex [(L3)ReO] is isolated and fully characterized after the reaction of the Re(V) precursor [ReOCl3(PPh3)2] with L3H3 (methyl 2-(4-((2-(2-hydroxyphenylamino)-2-oxoethylamino)methyl)-1H-1,2,3-triazol-1-yl)acetate). Its corresponding 99mTc-complex was achieved with a good radiochemical yield (>90%). The convenient synthesis of this ligand coupled with its high affinity for [ReO]3+ and [99mTcO]3+ cores make it a promising chelator for biomedical applications.