Thiolato-technetium complexes. 2. Synthesis, characterization, electrochemistry, and spectroelectrochemistry of the technetium(III) complexes trans-(Tc(SR) sub 2 (DMPE) sub 2 ) sup + , where R is an alkyl or benzyl group and DMPE is 1,2-Bis(dimethylphosphino)ethane

The use of a reduction-substitution route to prepare the thiolato-technetium(III) complexes trans-(Te(SR){sub 2}(DMPE){sub 2}){sup +} from the technetium(V) starting material trans-(Tc(OH)(O)(DMPE){sub 2}){sup 2+} and alkane- or benzenemethanethiols has been investigated (DMPE represents 1,2-bis(dimethylphosphino)ethane). The four newly prepared trans-(Tc(SR){sub 2}(DMPE){sub 2}){sup +} complexes (R = C{sub 2}H{sub 5}, n-C{sub 3}H{sub 7}, CH{sub 2}C{sub 6}H{sub 5}, CH{sub 2}C{sub 6}H{sub 4}-p-OCH{sub 3}) are characterized by fast atom bombardment mass spectrometry, visible-uv spectrophotometry, spectroelectrochemistry, and elemental analyses of three examples. They are assigned a trans geometry by comparison with the known structure of trans-(Tc(SCH{sub 3}){sub 2}(DMPE){sub 2}){sup +}. All five thiolato complexes exhibit a reversible Te(III/II) couple at about -0.5 V, a reversible Tc(II/I) couple at about -1.8 V, and an irreversible redox process at about +0.9 V that is tentatively assigned as resulting from a metal-based Tc(IV/III) couple (all potentials obtained in 0.5 M TEAP/DMF vs Ag/AgCl (3 M NaCl)). The potentials of all three couples are dependent on the nature of the thiolato R group; e.g., the Tc(III/II) couple varies from -0.513 V for R = benzyl to -0.622 V for R = n-propyl. For both the Tc(III) and Tc(II) complexes the visible spectra are dominated by sulfur-to-technetium charge-transfer transitions, the energies of which depend on the technetium oxidation state but do not depend on the nature of the thiolato R group. Observations on the relative instability of trans-(Tc(SCH{sub 3}){sub 2}(DMPE){sub 2}){sup +} in 0.5 M TEAP/DMF are interpreted in terms of the possible existence of the cis isomer of this complex. 25 refs., 6 figs., 4 tabs.