Technetium and Rhenium in Five-Coordinate Symmetrical and Dissymmetrical Nitrido Complexes with Alkyl Phosphino-thiol Ligands. Synthesis and Structural Characterization

Abstract

The reactivity of bulky alkylphosphino-thiol ligands (PSH) toward nitride-M(V, VI) (M = Tc/Re) precursors was investigated. Neutral five-coordinate monosubstituted complexes of the type [M(N)(PS)Cl(PPh(3))] (Tc1-4, Re1-2) were prepared in moderate to high yields. It was found that these [M(N)(PS)Cl(PPh(3))] species underwent ligand-exchange reactions under mild conditions when reacted with bidentate mononegative ligands having soft donor atoms such as dithiocarbamates (NaL(n)) to afford stable dissymmetrical mixed-substituted complexes of the type [M(N)(PS)(L(n))] (Tc5,8-10, Re5-9) containing two different bidentate chelating ligands bound to the [M[triple bond]N](2+) moiety. In these reactions, the dithiocarbamate replaced the two labile monodentate ligands (Cl and PPh(3)) leaving the [M(N)(PS)](+) building block intact. In the above reactions, technetium and rhenium were found to behave in a similar way. Instead, under more drastic conditions, reactions of PSH with [M(N)Cl(2)(PPh(3))(2)] gave a mixture of monosubstituted [M(N)(PS)Cl(PPh(3))] and bis-substituted species [M(N)(PS)(2)] (Tc11-14) in the case of technetium, whereas only monosubstituted [M(N)(PS)Cl(PPh(3))] complexes were recovered for rhenium. All isolated products were characterized by elemental analysis, IR and multinuclear ((1)H, (13)C, and (31)P) NMR spectroscopies, ESI MS spectrometry, and X-ray crystal structure determination of the representative monosubstituted [Tc(N)(PStbu)Cl(PPh(3))] (Tc4) and mixed-substituted [Re(N)(PScy)(L(3))] (Re7) and [Re(N)(PSiso)(L(4))] (Re9) complexes. The latter rhenium complexes represent the first example of a square-pyramidal nitrido Re species with the basal plane defined by a PS(3) donor set. Monosubstituted [M(N)(PS)Cl(PPh(3))] species bearing the substitution-inert [M(N)(PS)](+) moieties act as suitable building blocks proposed for the construction of new classes of dissymmetrical nitrido compounds with potential application in the development of essential and target specific (99m)Tc and (188)Re radiopharmaceuticals for imaging and therapy, respectively.

Dithiocarbamate complexes as radiopharmaceuticals for medical imaging

“…A series of complexes based on the [TcN] 2+ core with one bidentate phosphine-thiol (PS) ligand and one dithiocarbamate with the general square pyramidal structure [TcN(PS)(DTC)] (16) (figure 4) has been reported [70–72]. Analogues of these complexes containing lipophilic dithiocarbamates such as DEDTC and dipropyldithiocarbamate (DPDTC) and lipophilic side chains on the PS ligand were able to cross the blood brain barrier [71], but attempts to exploit this by incorporation of dithiocarbamate derivatives of 2-methoxyphenylpiperazine to produce agents for imaging 5HT 1A receptors in brain led to reduced blood brain barrier penetration [72].…”

Syntheses and Structures of Nitridorhenium(V) and Nitridotechnetium(V) Complexes with N,N‐[(Dialkylamino)(thiocarbonyl)]‐N′‐(2‐hydroxyphenyl)benzamidines

“…The absence of absorptions in the regions around 3350 cm –1 and 3150 cm –1 , in which the ν NH and ν OH stretches are detected in the spectra of the uncoordinated H 2 L 1 , indicates the expected double deprotonation of the ligands during complex formation. Absorption bands of medium intensity around 1065 cm –1 are assigned to Re≡N and Tc≡N stretches 7…”

Nitrido Technetium-99 m Core in Radiopharmaceutical Applications: Four Decades of Research

“…In this case, the coordination geometry around Tc is intermediate between sp and tbp. In the tbp description, the nitrido group, the chloride and the thiolate sulfur atoms occupy the equatorial plane, while the two phosphine phosphorus atoms are at the apexes of the bypyramid [21,41]. [98,99].…”