A mechanistic study of sulphur, nitrogen and oxygen donor bidentate ligand interactions on the rhenium (I) tricarbonyl core

[摘要] English: The nuclear properties of rhenium (186/188Re) and technetium (99mTc) are used for theirapplication as diagnostic and therapeutic radiopharmaceuticals. Researchers haveshown a significant interest in rhenium and technetium tricarbonyl complexes of theform fac-[M(CO)3X(L,L'-Bid)]n where M = Tc(I) or Re(I), X = entering monodentateligand and L-L'-Bid = different donor atom bidentate ligands, as potential diagnosticand therapeutic radiopharmaceuticals. These fac-[M(CO)3X(L,L'-Bid)]n type complexesare prepared from the starting synthons fac-[M(CO)3(Br3)]2- and fac-[M(CO)3(H2O)3]+that was initially prepared by Alberto et al. in 1999. This starting synthon is a favouriteall around for the synthesis of potential radiopharmaceuticals due to the easypreparation and the stability of fac-[M(CO)3(H2O)3]+ in aqueous solution in the pHrange of 2 - 12 for several hours. The carbonyl ligands are tightly coordinated to themetal and form the stable fac-[M(CO)3]+ core. The three bromido or water ligands canbe easily substituted by different functional groups such as thioethers, thiols,phosphines and amines.The aim of this study was to investigate the ability of the chosen donor atom N,O; S,S';S,O bidentate and S,S'S tridentate ligands to coordinate to the fac-[Re(CO)3]+ core.The results were compared to previous studies reported on N,O and O,O' bidentateligand systems to observe the variation in coordination behaviours. The chosen ligandsinclude: 5-phenylazo-8-hydroxyquinoline, 5-(m-Tol)azo-8-hydroxyquinoline, 5-(2,3-diMephenyl)azo-8-hydroxyquinoline, 5-(2,6-diMe phenyl)azo-8-hydroxyquinoline, 5-(3,4-diMe phenyl)azo-8-hydroxyquinoline, methyl benzo[b]thiophene-2-carboxylate,benzothiophene-2-methanol, 2-mercaptophenol, 2-methoxythiophenol, 5-bromo-2,2`-bithiophene, 2,2�?bithiophene-5-carboxylic acid, benzene-1,2-dithiol, toluene-3,4-dithiol, and 2,2`-thiodiethanethiol.The synthesis of the complexes are described in Chapter 4 and characterized by IR,UV/Vis, NMR (1H and 13C) and elemental analysis. The following crystal structureswere obtained fac-[Re2(CO)6(TS)(Py)] (1), fac-[Re2(CO)6PPh3(BSOPhC)2(Py)] (2), fac-[NEt4][Re2(CO)6(BSOPhC)3] (3) and fac-[Re2(CO)6(m-TolBSPh)2] (4). All four of thestructures has four molecules per unit cell (Z = 4). (1) and (4) crystallized in the P1̅space group while (2) and (3) crystallized in a monoclinic space group. In all four thesestructures the ligands form sulphur bridges between two rhenium (I) centres. The Re-CO bond distances of all the crystal structures range from 1.88(3) Å to 1.95(10) Å andthe Re-S bond distances vary from 2.44(2) Å to 2.56(7) Å. (2) has a Re-P bond distanceof 2.51(12) Å and a Re-N bond distance of 2.24(4) Å. The S-Re-S bond angles rangefrom 76.26(3) ° to 94.99(8) ° and the Re-S-Re bond angles from 87.28(9) ° to 100.60(4)° with the non-bonding rhenium to rhenium distances of 3.796(8) Å for (1), 3.845(10)Å for (2), 3.488(10) Å for (3) and 3.654(16) Å for (4). The non-bonding Re…Redistances are directly proportional to the Re-S-Re angles and follow the following trend:(3) < (4) < (1) < (2).A fairly good comparison could be made between previously reported structures withS,S'; S,O; N,O and O,O'-bidentate ligands coordinated to the fac-[Re(CO)3]+ core. Thestructure of (4) has been reported before and a very good correlation is found betweenthis structure and the reported structure.After an in depth study it was confirmed that the structures of all the compounds withS,O; S,S' and S,S',S'' ligands have to be analysed by single crystal XRD or at least aquantitative NMR study. For one ligand system (BSOPhC), two different structureswere obtained with only a slight change in the synthetic procedure. It is not that easyto determine and speculate the bonding modes of these type of ligands. Therefore acomplete crystallographic study will form part of the future work for this project.Excellent results were obtained for anti-mitochondrial activity screening for fivecompounds. The next step will be to improve the solubility of these complexes,especially in water as solvent; this illustrates the possible use of these compounds aspotential radiopharmaceuticals.

[发布机构] University of the Free State