Structural and ⁹⁹Tc NMR Investigations of Complexes with fac-[Tc(CO)₃]⁺ Moieties and Macrocyclic Thioethers of Various Ring Sizes:  Synthesis and X-ray Structure of the Complexes fac-[Tc(9-ane-S₃)(CO)₃]Br, fac-[Tc₂(tosylate)₂(18-ane-S₆)(CO)₆], and fac-[Tc₂(20-ane-S₆-OH)(CO)₆][tosylate]₂

Abstract

Starting originally from the organometallic precursor [NEt(4)](2)[TcBr(3)(CO)(3)] (1b), substitution reactions were performed with the macrocyclic thioethers 1,4,7-trithiacyclononane (9-ane-S(3)), 1,4,7,10,13,16-hexathiacyclooctadecane (18-ane-S(6)), and 3,6,9,13,16,19-hexathiacycloicosanol (20-ane-S(6)-OH). The corresponding complexes fac-[Tc(9-ane-S(3))(CO)(3)]Br (2), fac-[Tc(2)(tosylate)(2)(18-ane-S(6))(CO)(6)] (3), and fac-[Tc(2)(20-ane-S(6)-OH)(CO)(6)][tosylate](2) (5) were isolated in good yields and characterized spectroscopically by IR, (1)H, (99)Tc NMR, and X-ray diffraction methods. In the case of 18-ane-S(6) and 20-ane-S(6)-OH the formation of the 1:2 as well as the 1:1 complex could be observed in the (99)Tc NMR experiment, depending on the ligand to metal ratio. Complex 2crystallizes in the monoclinic space group P2(1)/c, a = 14.79(2) Å, b = 11.691(2) Å, c = 16.94(2) Å, beta = 94.88(6) degrees, Z = 8. The tripodal ligand is coordinated through the sulfur atoms to the metal center, forming three favorable five-membered chelate rings. Complex 3 crystallizes in the monoclinic space group C2/c, a = 26.073(4) Å, b = 9.288(1) Å, c = 17.898(3) Å, beta = 99.84(1) degrees, Z = 4. The binuclear unit is formed by two fac-[Tc(tosylate)(CO)(3)] moieties which are trans, bidentate coordinated to the macrocyclic ligand. Compound 5 crystallizes in the monoclinic space group Pc, a = 25.737(4) Å, b = 14.009(1) Å, c = 26.479(3) Å, beta = 149.56(2) degrees, Z = 4. In the case of the dicationic compound 5, the two Tc(I) centers are tripodal, cis coordinated toward the thia crown ether. A detailed analysis of the ring conformation in the solid state structure explained to a certain extent the formation of only one isomer (trans in the case of 3 and cis in the case of 5, respectively) during the substitution reaction.

Diagnostic Nuclear Medicine

“…Extensive research by the groups of Schubiger αnd Alberto (Alberto et al 1998a) has resulted in the successful development 3 ) + via the reduction of Na 99m TcO 4 with sodium borohydride at pH 11 under an atmosphere of carbon monoxide. This cationic species readily undergoes ligand exchange of coordinated water with a wide variety of donor ligands, of which the tridentate ligands such as histidine yield the most stable complexes (Abram et al 1992;Schibli et al 1998Schibli et al , 2000. The net charge of the final complex can be -1, 0 or +1 depending on the nature of the coordinating ligand.…”

Biodistribution of99mTc Tricarbonyl Glycine Oligomers

“…In attempt to overcome this undesirable conjugation, currently single amino acid chelate (SAAC) systems for the incorporation of the 99m Tc-tricarbonyl-based radiopharmaceuticals have been successfully established into novel synthetic strategies (Maresca et al ., 2010). During the past decade, the field of technetium coordination chemistry has seen a rising interest in the 99m Tc-tricarbonyl core (Schibli et al ., 1998; Schibli et al ., 2001). But the hydrophobicity of the metal complexes resulted in poor pharmacokinetic profile.…”

Technetium‐99m radiochemistry for pharmaceutical applications

“…Both the (N,S,N) and (N,S,O) chelators may lead to diasteromers due to the prochirality of thioether sulfur if there is an additional chiral center . Thioether (N,S,S) and (S,S,S) ligands have also been developed …”

“…[88][89][90][91][92][93] Thioether (N,S,S) and (S,S,S) ligands have also been developed. 78,94 Phosphine-containing ligands, with (P,N,P), (P,S,S), and (P,O,O) donor atoms ( Figures 16.5 and 17), have been used to form in vivo stable [ 99m Tc(CO) 3 ] complexes in high yields. [95][96][97] Ligands may also contain the water-soluble, air stable hydroxymethylphosphine.…”