2+1 Tricarbonyl Complexes of Technetium(I) with a Combination of N,N-Bidentate Ligands and Ethyl Isocyanoacetate: How Strong Is the Interfering Effect of Chloride Ions on Their Formation?

Technetium(I) 2 + 1 tricarbonyl complexes with a combination of N,N-bidentate ligands (2,2'-bipyridine, bipy; 1,10phenanthroline, phen) and ethyl isocyanoacetate were prepared and characterized by NMR, IR, UV/visible, and luminescence spectroscopies and by high-performance liquid chromatography (HPLC). The crystal structures of [Tc-99(CO)(3)(bipy)(CNCH2COOEt)](ClO4) (in the form of a solvate with 0.5CH(2)Cl(2)) and [Tc-99(CO)(3)(phen)-(CNCH2COOEt)](ClO4) (in the form of an adduct with an outer sphere phen molecule) were determined by single-crystal X-ray diffraction. To evaluate the interfering effect of chloride ions on the formation of the 2 + 1 complexes, the kinetics of the replacement of labile monodentate ligand X in the complexes [MX(CO)(3)((NN)-N-?)] (M = Re, Tc-99; (NN)-N-? = bipy, phen; X = Cl- , ClO4- ) by CNCH2COOEt in ethanol were compared. The Tc-99 bipy complexes with X = ClO4- (according to the IR data, perchlorate anion in ethanol is displaced from the coordination sphere by the solvent molecule) and X = Cl- are characterized by close ligand replacement rates. In the case of the Tc-99 complexes with phen and Re complexes with both phen and bipy, the chloride complexes are appreciably less reactive than the chloride-free complexes. The technetium complexes are considerably more reactive in ligand replacement than their rhenium analogues. In the chloride-containing medium (saline), the complex [(99)mTc(CO)(3)(bipy)(CNCH2COOEt)](+) can be prepared under the conditions acceptable for nuclear medical applications, although higher isonitrile concentrations are required as compared to the chloride-free system.

Automated summary

In this study, tricarbonyl complexes of technetium(I) 2 + 1 were synthesized and characterized using various techniques. The crystal structures of two complexes were determined by single-crystal X-ray diffraction. The effect of chloride ions on the formation of the complexes was evaluated, and it was found that the chloride complexes were less reactive compared to the chloride-free complexes. The technetium complexes exhibited higher reactivity than their rhenium analogues.