Synthesis and Characterization of Novel Oxotechnetium (⁹⁹Tc and ^99mTc) and Oxorhenium Complexes from the 2,2‘-Bipyridine (NN)/Thiol (S) Mixed-Ligand System

The synthesis and characterization of oxotechnetium and oxorhenium mixed-ligand complexes of the general formula MO[NN][S]3 (M = 99Tc and Re), where NN represents the bidentate ligand 2,2‘-bipyridine and S represents a monodentate thiophenol, is reported. The complexes were prepared by ligand exchange reactions using 99Tc-gluconate and ReOCl3(PPh3)2 as precursors for the oxotechnetium and oxorhenium complexes, respectively. Compound 1 (M = 99Tc, S = 4-methylthiophenol) crystallizes in the monoclinic space group P21/a, a = 23.12(1) Å, b = 14.349(6) Å, c = 8.801(4) Å, β = 94.81(2)°, V = 2918(2) Å3, Z = 4. Compound 3 (M = Re, S = 4-methylthiophenol) crystallizes in the monoclinic space group P21/a, a = 23.018(9) Å, b = 14.421(5) Å, c = 8.775(3) Å, β = 94.78(1)°, V = 2903(2) Å3, Z = 4. Compound 4 (M = Re, S = 4-methoxythiophenol) crystallizes in the orthorhombic space group Pbca, a = 16.32(1) Å, b = 24.55(2) Å, c = 16.94(1) Å, V = 6788(9) Å3, Z = 8. In all cases, the coordination geometry around the metal is distorted octahedral with the equatorial plane being defined by the three sulfur atoms of the thiophenols and one nitrogen atom of 2,2‘-bipyridine, while the apical positions are occupied by the second nitrogen atom of 2,2‘-bipyridine and the oxygen of the MO core. The complexes are stable, neutral, and lipophilic. Complete 1H and 13C NMR assignments are reported for all complexes. The analogous oxotechnetium complexes have been also synthesized at tracer level (99mTc) by mixing the 2,2‘-bipyridine and the corresponding thiol with Na99mTcO4 generator eluate using NaBH4 as reducing agent. Their structure was established by chromatographic comparison with authentic oxotechnetium and oxorhenium complexes using high performance liquid chromatography techniques