Syn−Anti Isomerism in a Mixed-Ligand Oxorhenium Complex, ReO[SN(R)S][S]

Abstract

The simultaneous action of the tridentate ligand (C(2)H(5))(2)NCH(2)CH(2)N(CH(2)CH(2)SH)(2) and the monodentate coligand HSC(6)H(4)OCH(3) on a suitable ReO(3+) precursor results in a mixture of syn- and anti-oxorhenium complexes, ReO[(C(2)H(5))(2)NCH(2)CH(2)N(CH(2)CH(2)S)(2)] [SC(6)H(4)OCH(3)], in a ratio of 25/1. The complexes are prepared by a ligand exchange reaction using ReO(eg)(2) (eg = ethylene glycol), ReOCl(3)(PPh(3))(2), or Re(V)-citrate as precursor. Both complexes have been characterized by elemental analysis, FT-IR, UV-vis, X-ray crystallography, and NMR spectroscopy. The syn isomer C(17)H(29)N(2)O(2)S(3)Re crystallizes in the monoclinic space group P2(1)/n, a = 14.109(4) Å, b = 7.518(2) Å, c = 20.900(5) Å, beta = 103.07(1) degrees, V = 2159.4(9) Å(3), Z = 4. The anti isomer C(17)H(29)N(2)O(2)S(3)Re crystallizes in P2(1)/n, a = 9.3850(7) Å, b = 27.979(2) Å, c = 8.3648(6) Å, beta = 99.86(1) degrees, V = 2163.9(3) Å(3), Z = 4. Complete NMR studies show that the orientation of the N substituent chain with respect to the Re=O core greatly influences the observed chemical shifts. Complexes were also prepared at the tracer ((186)Re) level by using (186)Re-citrate as precursor. Corroboration of the structure at tracer level was achieved by comparative HPLC studies.

Novel Oxorhenium and Oxotechnetium Complexes from an Aminothiol[NS]/Thiol[S] Mixed-Ligand System

“…The major product was eluted at 18 minutes and the minor one at 22 minutes. These retention times were the same as those of the oxorhenium complexes [ReO(L n )(L) 3 ] (1, 2) and [ReO(L n )(L) 2 ] (3,4) suggesting the formation of analogous oxotechnetium complexes, [ 99g TcO(L n )(L) 3 ] (5, 6) and [ 99g TcO(L n )(L) 2 ] (7,8). Three days later, HPLC analysis showed that the peak at 22 minutes became the predominant peak ( Figure 2 trace B) indicating a quantitative transformation of complexes 5 and 6 ([ 99g TcO(L n )(L) 3 ]) to 7 and 8 ([ 99g TcO(L n )(L) 2 ]) respectively.…”

“…Meanwhile, in each case, a crystalline product precipitated with an HPLC retention time of 22 minutes (Figure 2 trace C). Elemental analysis, X-ray crystallography, and spectroscopic methods confirm that the crystalline complexes were [ 99g TcO{(CH 3 CH 2 ) 2 NCH 2 CH 2 S}-(SC 6 H 4 OCH 3 ) 2 ] (7) in the case of the L 1 H and [ 99g TcO(C 5 H 10 NCH 2 CH 2 S)(SC 6 H 4 OCH 3 ) 2 ] (8) in the case of the L 2 H ligand. We are once again led to the conclusion that the [ 99g TcO(L n )(L) 3 ] complexes gradually convert to the [ 99g TcO(L n )(L) 2 ] complexes.…”

“…have been previously reported. [8,15,19] Elemental analyses were performed on a Perkin ± Elmer 2400/II automatic analyzer. 99g Tc was purchased as ammonium pertechnetate from the Oak Ridge National Laboratory.…”

“…The NMR spectra of 3, 4, 7, and 8 displayed the basic characteristics of the aminothiol complexes observed in our previous studies. [8,18,19] Specifically: All geminal protons of the aminothiol ligand, being diastereotopic, exhibit distinct chemical shifts. Protons of the S À C1 À C2 À N part, being on the same side as the oxygen of the oxometal core (endo protons), generally appear downfield relative to those on the opposite side (exo protons) with Dd reaching up to 1.2 ppm in these types of complexes.…”

“…[6] Since sulfhydryl-containing ligands provide ideal molecules for the synthesis of oxorhenium and oxotechnetium complexes, our interest is currently focused [7] on the investigation of other mixed-ligand systems that contain thiol residues, among which are the bidentate aminothiol [NS] and monodentate thiol [S] ligand systems. In contrast to the ª31º mixed-ligand system SN(R)S/S, [5,8] the formation of stereoisomers can be avoided by symmetric substitution on the nitrogen of the aminothiol ligand, while the advantages of the ª31º system still remain.…”