Synthesis, Characterisation and Structural Analysis of Rhenium and Technetium Nitride Complexes With Tridentate Thiosemicarbazone‐Phenols and Phosphine Ligands: Potential Applications in Technetium‐99m Radiotracer Development
Source: PubMed Central Open Access, NCBI / U.S. National Library of Medicine
The reactivity of two tridentate salicylthiosemicarbazones (HL1 = 3‐methoxysalicylaldehyde thiosemicarbazone; HL2 = 3‐methoxysalicylaldehyde N,N‐dimethyl‐thiosemicarbazone), with the [M≡ N]core (M = Re,Tc), is here described, leading to the formation of heteroleptic complexes of the general composition [MN(L)P] (P = triphenylphosphine, PPh; tris(2‐cyanoethyl)phosphine, PCN). The [ReN(L)PPh] complexes were prepared in good yield starting from [ReNCl(PPh)] precursor and in lower quantity from (BuN)[ReNCl]. Complexes were fully characterised by elemental analyses, spectroscopic, spectrometric techniques and X‐ray diffraction. Single‐crystal X‐ray diffraction analysis of [ReN(L1)PPh] and [ReN(L2)PPh] showed the formation of a distorted square base pyramid geometry with the rhenium atom located 0.57 Å above the pyramid base and the nitride ion in apical position. The basal plane is occupied by the S,N,O‐thiosemicarbazonate and the triphenylphosphine ligands. Superimposable complexes were obtained in high yield at tracer level with technetium‐99m and under carried‐added conditions. In technetium complexes, triphenylphosphine can be successfully replaced with PCN, forming corresponding complexes in high yield; this substitution was unfeasible with cold rhenium. Based on the collected preliminary results, it is reasonable to assume that [Tc][TcN(L)P] (L = bisdeprotonated ligand; P = monophosphine) could be a promising platform for developing new potential technetium‐99m‐based radiotr
Abstract
The reactivity of two tridentate salicylthiosemicarbazones (HL1 = 3‐methoxysalicylaldehyde thiosemicarbazone; HL2 = 3‐methoxysalicylaldehyde N,N‐dimethyl‐thiosemicarbazone), with the [M≡ N]core (M = Re,Tc), is here described, leading to the formation of heteroleptic complexes of the general composition [MN(L)P] (P = triphenylphosphine, PPh; tris(2‐cyanoethyl)phosphine, PCN). The [ReN(L)PPh] complexes were prepared in good yield starting from [ReNCl(PPh)] precursor and in lower quantity from (BuN)[ReNCl]. Complexes were fully characterised by elemental analyses, spectroscopic, spectrometric techniques and X‐ray diffraction. Single‐crystal X‐ray diffraction analysis of [ReN(L1)PPh] and [ReN(L2)PPh] showed the formation of a distorted square base pyramid geometry with the rhenium atom located 0.57 Å above the pyramid base and the nitride ion in apical position. The basal plane is occupied by the S,N,O‐thiosemicarbazonate and the triphenylphosphine ligands. Superimposable complexes were obtained in high yield at tracer level with technetium‐99m and under carried‐added conditions. In technetium complexes, triphenylphosphine can be successfully replaced with PCN, forming corresponding complexes in high yield; this substitution was unfeasible with cold rhenium. Based on the collected preliminary results, it is reasonable to assume that [Tc][TcN(L)P] (L = bisdeprotonated ligand; P = monophosphine) could be a promising platform for developing new potential technetium‐99m‐based radiotracers. However, improvements in labelling efficiency and stability must be addressed to fully realise its potential.