Structural models for [M(CO)3(H2O)3]+ (M=Tc, Re): fully aqueous synthesis of technetium and rhenium tricarbonyl complexes of tripodal oxygen donor ligands

fac-[Re(CO)3(dmso-O)3](CF3SO3): a new versatile and efficient Re(i) precursor for the preparation of mono and polynuclear compounds containing fac-[Re(CO)3]+ fragments

We show here that the new complex fac-[Re(CO)3(dmso-O)3](CF3SO3) (1), efficiently prepared in one step from [ReBr(CO)5] and featuring a broad range of solubility, is, in general, a better precursor for the one-step synthesis of mono- and polynuclear inorganic compounds containing fac-[Re(CO)3]+ fragments compared to the commonly used (NEt4)2fac-[ReBr3(CO)3] and fac-[Re(CO)3(CH3CN)3](Y) (Y = PF6, BF4, ClO4) species. Compound 1 is the first example of a Re(I)-dmso complex structurally characterized and confirms the rule that dmso is always O-bonded when trans to CO. The reactivity of 1 was tested in the one-step preparation of several new and known complexes. The O-bonded sulfoxides of 1 are replaced under mild conditions by tri- (L3) and bidentate ligands (L2) to produce fac-[Re(CO)3(L3)]+ and fac-[Re(CO)3(L2)(dmso-O)]+ compounds, respectively. An excess of monodentate ligands (L) and more forcing conditions are needed to prepare fac-[Re(CO)3(L)3]+ compounds. The new compounds include fac-[Re(CO)3(bipy)(dmso-O)](CF3SO3) (4), that turned out to be an excellent precursor for binding the luminescent fac-[Re(CO)3(bipy)]+ fragment to polytopic ligands for the construction of more elaborate assemblies. One example reported here is the two-step preparation of fac-[{Re(CO)3(bipy)}(mu-4,4'-bipy){Ru(TPP)(CO)}](CF3SO3) (8) (TPP = tetraphenylporphyrin). The X-ray structures of the new compounds 1, 4, of the bis-porphyrin complex fac-[Re(CO)3Cl(4'MPyP)2] (13) (4'MPyP = 5-(4'pyridyl)-10,15,20-triphenylporphyrin), and of the rhenium-cyclophane [{(CO)3Re(mu-OH)2Re(CO)3}2(micro-4,4'-bipy)2] (15), among others, are described. Compound 1 might find useful applications in supramolecular chemistry (metal-mediated assembly of large architectures), in the in situ preparation of stable Re compounds to be used in nuclear medicine, and for the labeling of biomolecules.

Identification of the non-pertechnetate species in Hanford waste tanks, Tc(I)--carbonyl complexes

Immobilization of the high-level nuclear waste stored at the Hanford Reservation has been complicated by the presence of soluble, lower-valent technetium species. Previous work by Schroeder and Blanchard has shown that these species cannot be removed by ion-exchange and are difficult to oxidize. The Tc K-edge XANES spectra of the species in Tanks SY-101 and SY-103 were reported by Blanchard, but they could not be assigned to any known technetium complex. We report that the XANES spectra are most likely those of Tc(I)-carbonyl species, especially fac-Tc(CO)3(gluconate)(2-). This is further supported by EXAFS and 99Tc-NMR studies in nonradioactive simulants of these tank wastes.

Versatile synthetic approach to new bifunctional chelating agents tailor made for labeling with the fac-[M(CO)(3)](+) core (M = Tc, (99m)Tc, Re): synthesis, in vitro, and in vivo behavior of the model complex [M(APPA)(CO)(3)] (APPA = [(5-amino-pentyl)-pyridin-2-yl-methyl-amino]-acetic acid)

A general synthetic approach for potent tridentate, bifunctional chelating agent (BFCA) for the [M(CO)(3)](+) fragment (M = (99g)Tc, (99m)Tc, and Re) has been elaborated. The strategy allows the facile preparation of BFCA with a pendent amino or carboxylic acid functionality for coupling to peptides and proteins via formation of an amide bond. [(5-amino-pentyl)-pyridin-2-yl-methyl-amino]-acetic acid (APPA) and [pyridin-2-yl-methyl-amino]-diacetic acid (PADA) were synthesized according to this protocol. The BFCA were labeled with the [M(CO)(3)](+) fragment, which resulted in formation of uniform products with a ligand to metal ratio of 1:1. The complexes have been fully characterized by means of mass spectrometry, IR, and NMR ((1)H, (13)C, (99)Tc) spectroscopy. Coordination of the tricarbonyl core with APPA and PADA was exclusively tridentate (via the acid function, the ternary amine, and the pyridine nitrogen). On the n.c.a. level the complexes were almost quantitatively formed (yield >90%) at ligand concentrations of 10+/-2 microM (PADA) or 50+/-4 microM (APPA) after 30 min at 70 degrees C. Chromatographic behavior of the (99m)Tc complexes is similar to that of the corresponding (99)Tc/Re complexes suggesting the identical chemical structure. Pharmacokinetic experiments with the (99m)Tc-APPA complex were performed in BALB/c mice and compared with previously published results of the (99m)Tc-PADA complex. The (99m)Tc-APPA complex revealed good clearance from the blood pool (0.29 +/- 0.03% ID after 24h p.i.) and a low uptake in the liver (2.41 +/- 0.14% ID/g), in the kidneys (2.81 +/- 0.12% ID/g) and other tissue and organs.

N-(2-Mercaptoethyl)picolylamine as a diaminomonothiolate ligand for the "fac-[Re(CO)3]+" core

N-(2-Mercaptoethyl)picolylamine (MEPAH) was studied as a potentially biologically relevant ligand for the "fac-[M(CO)(3)](+)" core (M = Re, (99)Tc, (99m)Tc). To this end, the complex Re(CO)(3)(MEPA) was synthesized. The reaction of MEPAH with fac-[Re(CO)(3)(MeCN)(3)](+) took place over the course of seconds, showing the high affinity possessed by this ligand for the "fac-[Re(CO)(3)](+)" core. A single-crystal X-ray diffraction study was performed confirming the nature of Re(CO)(3)(MEPA), a rare mononuclear rhenium(I) thiolate complex. Additional exploration into derivatization of the ligand backbone has afforded the analogous N-ethyl complex, Re(CO)(3)(MEPA-NEt). The high affinity of the ligand for the metal coupled with the ease of its derivatization implies that utilization of this ligand system for the purposes of (99m)Tc-radiopharmaceutical development is promising.