posted on 2013-11-20, 00:00authored byMichael Benz, Bernhard Spingler, Roger Alberto, Henrik Braband
99TcVO2–NHC complexes containing
monodentate and bidentate N-heterocyclic carbenes (NHCs) have been
prepared by the reactions of [TcO(glyc)2]− (glyc = ethyleneglycolato) with 1,3-dimethylimidazoline-2-ylidene
(L1), 1,1′-methylene-3,3′-dimethyl-4,4′-diimidazoline-2,2′-diylidene
(L2), and 1,1′-methylene-3,3′-diethyl-4,4′-diimidazoline-2,2′-diylidene
(L3) in THF. The resulting complexes were fully characterized
and their stabilities investigated. While complexes with monodentate
NHCs only are hydrolytically unstable, complexes containing bidentate
NHCs are water-stable over a broad pH range. The high water stability
allows interconversion of the {99TcVO2}+ core into {99TcVOCl}2+ with HCl as the H+ and Cl– source.
An alternative procedure to obtain 99TcVO2–NHC complexes is the in situ deprotonation of imidazolium
salts, enabling the preparation of 99TcVO2–NHC compounds without free NHCs, thus increasing the
scope of NHC ligands drastically. The remarkable stability and pH-controllable
reactivity of the new complexes underlines the potential of NHCs as
stabilizing ligands for 99Tc complexes and paves the way
for the first 99mTc–NHC complexes in the future.