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

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