Synthesis, characterization and stability studies of some potential brains seeking agents-trialkyl (triaryl) siloxyalkyl(aryl)-thiolato-3-thiapentane-1,5-dithialato oxorhenium(V) complexes.

Neutral lipophilic silicon organic compound of oxorhenium complexes were obtained by the "3+1" mixed ligand approach with the simultaneous complexation of one SSS tridentate ligand and a monodentate S-R ligand with the formation of the oxorhenium(V) complexes. Four trialkyl(triaryl)siloxyalkane(benzene)thiolato-(3-thiapentane-1,5-dithiolato)oxorhenium complexes of the general formula (SCH₂CH₂SCH₂CH₂S) ReO (SQOSiR₃) were synthesized and studied where
IV, Q = CH₂CH₂, R = CH₂ CH₃
V, Q = CH₂CH₂ CH₂, R = CH₂ CH₃
VI, Q = C₆H₅, R = CH₂CH₃
VII, Q = CH₂CH₂, R = C₆H₅
Identification and determination of structure of the compounds (IV-VII) and hydrolized products (I-III) were carried out by TLC, HPLC, elemental analysis and IR, UV and NMR spectroscopic methods. Lipophilicity was determined by reverse phase HPLC method. As a role the more lipophilic compounds should have stronger binding with the C18 chain of the column material giving higher retention time. The retention time of the silicon rhenium complexes(IV-(VII) and the corresponding OH compounds (I-III) of the general formula (SCH₂CH₂SCH₂CH₂S)ReO(SQOH) where I, Q= CH₂ CH₂, II, Q= CH₂CH₂ CH₂, R = III, Q=C₆H₅, were determined as

Compound.....Retention time (min)..............Compound.......Retention time (min)
I.....................2.60.....................................IV....................4.16
II....................2.64......................................V....................4.26
III...................2.87......................................VI....................4.46
I.....................2.60......................................VII.................. 4.93

It observed that the retention time of the compounds increases with the increase of lipophilicity as expected on the reverse phase column and the introduction of alkyl or arylsilyl radical to the oxygen atom greatly increases the lipophilicity. Stability of the silicon rhenium complexes (IV-VII) was studied in acetonitrile-water solution at different temperature and pH by reverse phase HPLC method. Of the four compounds triethylsiloxyalkylthiolato (IV and V) complexes were found to be the most stable with respect to both temperature and pH changes. Trialkylphenylsiloxy compound (VI) was found to be most unstable one. All the compounds were labile in acidic pH. The most lipophilic compound (VII) was less soluble in acetonitrile-water (1:1) system.