Study on the formation of mixed ligand oxorhenium and oxotechnetium complexes (SNS/S combination)

Theoretically, the reaction of the tridentate aminedithiol ligand EtN(CH₂CH₂SH)₂, L1H₂, and the monodentate thiol 4-ClC₆H₄SH, L2H, with the Re^VOCl₃(PPh₃)₂ may lead to the formation of the following complexes: (i) neutral mixed ligand complexes ReOL1L2 (the syn isomer, complex 1 and the anti isomer, complex 2, (ii) binuclear complex of the tridentate ligand, (MO)₂(L1)₃, complex 3, and (iii) anionic complex of the monothiol [MO(L2)₄]^-, complex 4. When a mixture of L1H₂/L2H, 1/1 ratio, is applied, the major product of the reaction is the syn isomer 1. A small amount of the anti isomer 2 is also isolated (yield < 2 %) while none of the complexes 3 and 4 form during the reaction under the above conditions. The oxorhenium complexes 3 and 4 have been synthesized by the reaction of L1H₂ or L2H with the precursor ReOCl₃(PPh₃)₂. The crystal structure of 1, 3, and 4 is determined by X-ray crystallography. The corresponding Tc-99m complexes have been prepared by exchange reaction using Tc-99m glucoheptonate as precursor. Similarly the major reaction product is the syn isomer, complex 1´, while none of the other complexes form during the reaction at tracer level. The above studies demonstrate that simultaneous action of a tridentate SNS ligand and a monodentate thiol in equimolar quantities on Re^VOCl₃(PPh₃)₂ or Tc-99m glucoheptonate leads to a single rhenium or technetium-99m species, the syn MOL1L2.