Synthesis and characterization of novel trigonal-bipyramidal technetium(III) mixed-ligand complexes with SES/S/P coordination (E = O, N(CH₃), S)

Five-coordinate oxotechnetium(V) mixed-ligand complexes [TcO(SES)(S-p-C₆H₄-OMe)], where SES is a tridentate dithiolato fragment of the type ^-S(CH₂)₂E(CH₂)₂S^- (E = O, 1; E = S, 2; E = NMe, 3) are converted via reduction-substitution reactions in the presence of PMe₂Ph into the corresponding five-coordinate Tc(III) complexes [Tc(SES)(S-p-C₆H₄-OMe)(PMe₂Ph)] (E = O, 4; E = S, 5; E = NMe, 6). Rearrangement of the original square pyramidal '3 + 1' oxo-species to the trigonal bipyramidal '3+1+1' Tc(III) complexes occurs by placing the three thiolate donors on the basal plane, the phosphine phosphorus and the heteroatom of the tridentate ligand at the apexes of the bipyramid. These Tc(III) complexes are diamagnetic species, thereby allowing multinuclear NMR characterization in solution, which confirm their structures to be identical to those observed in the solid state via X-ray determinations.