A New Donor Atom System [(SNN)(S)] for the Synthesis of Neutral Oxotechnetium(V) Mixed-Ligand Complexes

Abstract

A new approach to the "3 + 1" mixed ligand oxotechnetium complexes of the general formula TcOL1L2, with ligands (L1H(2)) containing the SNN donor set and various monodentate thiols as coligands (L2H) is reported. The ligands L1H(2) (1-3, general formula R(1)CH(2)CH(2)NHCH(2)C(R(2))(2)SH where R(1) = N(CH(3))(2) and R(2) = H in 1, R(1) = pyrrolidin-1-yl and R(2) = H in 2, and R(1) = piperidin-1-yl and R(2) = CH(3) in 3) act as tridentate SNN chelates to the TcO(3+) core, leaving open one coordination site cis to the oxo group. In the presence of a monodentate thiol (L2H) and using (99)Tc(V)-gluconate as precursor, the vacancy is filled by the thiol which acts as the coligand. With this approach four neutral oxotechnetium complexes (4-7, general formula TcO[R(1)CH(2)CH(2)NCH(2)C(R(2))(2)S][SR] where RSH = p-methoxybenzenethiol, or p-methylbenzenethiol or benzyl mercaptan) were prepared in high yield by reacting L1H(2) and L2H with Tc(V)-gluconate in a ratio 1:1:1. The complexes were characterized by elemental analysis and spectroscopic methods. Complete assignments of (1)H and (13)C NMR resonances were made for all complexes. X-ray crystallographic studies of 5 (R(1) = pyrrolidin-1-yl, R(2) = H, RSH = p-methylbenzenethiol) and 7 (R(1) = piperidin-1-yl, R(2) = CH(3), RSH = benzyl mercaptan) showed that the complexes crystallize in the monoclinic space group P2(1)/n (a = 10.223(1) Å, b = 9.283(1) Å, c = 18.337(2) Å, beta = 97.262(2) degrees, V = 1726.3(4) Å(3), Z = 4; a = 11.876(2) Å, b = 10.470(2) Å, c = 17.098(3) Å, beta = 105.990(4) degrees, V = 2043.8(6) Å(3), Z = 4, for 5 and 7, respectively). Complexes5 and 7 have distorted square pyramidal coordination geometry with the oxo ligand in the axial position. The steric requirements of the oxo group cause the Tc atom to be displaced 0.68 Å out of the mean equatorial plane of the NNSS donor atoms in both complexes.

Synthesis and characterization of oxorhenium(V)–‘3+1’ mixed thiolate [SNS]/[S] and [ONS]/[S] complexes. Crystal and molecular structures of [ReO(η3-SCH2C5H3NCH2S)(η1-C6H4Br-4-S)], [ReO(η3-SCH2C5H3NCH2O)(η1-C6H4X-4-S)] (X=Cl, OMe), [ReO(η3-SCH2C5H3NCH2O)(η1-C6H4OCH3-4-CH2S)] and [ReO(η3-SCH2C5H3NCH2S)(η1-C5H4NH-2-S)][Cl]

“…However, germinal protons at the same methylene carbon of the tridentate [SNS] backbone were distinguished as endo (protons pointing toward the oxygen) and exo (protons pointing away from the oxygen) [22,23]. Proton resonances of the methylene backbone and pyridine ring were all shifted downfield.…”

“…As shown in Fig. 4, the structure of [ReO(η 3 -SCH 2 C 5 H 3 NCH 2 S)(η 1 -C 5 H 4 NH-2-S)][Cl] (22) consists of discrete complex cations and charge balancing Cl − anions. The nature of the ligand, specifically the steric requirement of the [SNS] tridentate ligand (4), the inability of the tridentate ligand to occupy the idealized equatorial positions while sterically blocking the sixth potential coordination position, possibly from the pyridyl nitrogen of potentially bidentate ligand, 2-mercaptopyridine, as well as the trans influence of the axial oxo-group, prohibits the formation of '3+2' complexation geometry [26].…”

“…Ellipsoids corresponds to 50% probability. ORTEP drawing of [ReO(η 3 -OCH 2 C 5 H 3 NCH 2 S)(η 1 -C 5 H 4 NH-2-S)][Cl] (22). Ellipsoids corresponds to 50% probability.…”

(Benzylthiolato-κS)phenylmercury(II)

“…1). Some complexes of the benzenemethanethiolato ligand have been reported previously (Wong et al, 2005;Papadopoulos et al, 1996;Berg et al, 1979). Sachs data reports has reported many organo-mercury mercaptides, including this complex, but the crystal structure data was not reported (Sachs, 1923).…”

The syntheses and structures of ‘3+2’ and ‘2+2+1’ oxorhenium mixed-ligand complexes employing 8-hydroxy-5-nitroquinoline as the bidentate N,O donor ligand

“…However, a downfield shift is always encountered in the '3+2' and '2+2+1' complexes 2-9. Due to the symmetry of complex 5, geminal protons at the same methylene carbon of the tridentate [ONS] backbone were distinguished as endo (protons pointing toward the Re=O oxygen) and exo (protons pointing away from the Re=O oxygen) [35,50,51]. Thus two doublets observed at 4.81 and 6.11 ppm were assigned to the endo and exo protons on the methylene thiolate backbone of the [ONS]/[NO] '3+2' complex 5.…”