SYN-ANTI ISOMERISM IN A MIXED-LIGAND OXORHENIUM COMPLEX, REO[SN(R)S][S]

The simultaneous action of the tridentate ligand (C2H5)(2)NCH2CH2N(CH2 CH2SH)(2) and the monodentate coligand HSC6H4OCH3 on a suitable ReO3precursor results in a mixture of syn- and anti-oxorhenium complexes, ReO-[(C2H5)(2)NCH2CH2N(CH2CH2S)(2)] [SC6H4OCH3], in a ratio of 25/1. T he complexes are prepared by a ligand exchange reaction using ReO(eg)( 2) (eg = ethylene glycol), ReOCl3(PPh(3))(2), or Re(V)-citrate as prec ursor. Both complexes have been characterized by elemental analysis, F T-IR, UV-vis, X-ray crystallography, and NMR spectroscopy. The syn iso mer C17H29N2O2S3Re crystallizes in the monoclinic space group P2(1)/n, a = 14.109(4) Angstrom, b = 7.518(2) Angstrom, c = 20.900(5) Angstrom , beta = 103.07(1)degrees, V = 2159.4(9) Angstrom(3), Z = 4. The anti isomer C17H29N2O2S3-Re crystallizes in P2(1)/n, a = 9.3850(7) Angstrom , b = 27.979(2) Angstrom, c = 8.3648(6) Angstrom, beta = 99.86(1)degre es, V = 2163.9(3) Angstrom(3), Z = 4. Complete NMR studies show that t he orientation of the N substituent chain with respect to the Re=O cor e greatly influences the observed chemical shifts. Complexes were also prepared at the tracer (Re-186) level by using Re-186-citrate as prec ursor. Corroboration of the structure at tracer level was achieved by comparative HPLC studies.