Abstract
The methanol substitution reactions of fac-[Re(2,5-PicoH)(CO)3(CH3OH)] (2,5-PicoH=pyridine-2-carboxylato-5-carboxylic acid) with a range of different entering ligands (Br− , I−, pyridine (Py), imidazole (Im) , thiocyanate (NCS−), thiourea (TU) and 1-methyl-2-thiourea (MeTU)) were investigated. The values for the second order rate constants, k1, follow a general trend in the order of N-donor ligands<halides<S-donating ligands. The rate constants for the reactions with TU and MeTU are almost 20 times larger than that of the N-donor ligands, indicating the seemingly higher affinity for the sulfur donating ligands. The starting complexes and substitution products were characterized by UV–Vis, IR and NMR spectroscopy and X-ray crystallographic studies of the compounds fac-[NEt4][Re(2,5-PicoH)(CO)3(Br)]·H2O (1) and fac-[NEt4][Re(2,5-PicoMe)(CO)3(Br)] (10) are reported. The synthesis of 10 is an example of a clean process to functionalize a ligand coordinated to a metal center. The radio labeling of 99mTc with pyridine-2-carboxylato-5-carboxylic acid was successful (Rt=18.22min).
Published Version
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