Thiol- and thioether-based bifunctional chelates for the {M(CO) 3}+ core (M = Tc, Re)

Neva Lazarova, John Babich, John Valliant, Paul Schaffer, Shelly James, Jon Zubieta

Research output: Contribution to journalArticle

51 Scopus citations

Abstract

By analogy to the recently described single amino acid chelate (SAAC) technology for complexation of the {M-(CO)3}+ core (M = Tc, Re), a series of tridentate ligands containing thiolate and thioether groups, as well as amino and pyridyl nitrogen donors, have been prepared: (NC5H4CH2)2NCH2CH 2SEt (L1); (NC5H4CH2) 2NCH2CH2SH (L2); NC5H 4CH2N(CH2CH2SH)2 (L3); (NC5H4CH2)N(CH2CH 2SH)(CH2CO2R) [R = H (L4); R = -C 2H5 (L5). The {Re(CO)3}+ core complexes of L1-L5 were prepared by the reaction of [Re(CO)3(H 2O)3]Br or [NEt4]2[Re(CO) 3Br3] with the appropriate ligand in methanol and characterized by infrared spectroscopy, 1H and 13C NMR spectroscopy, mass spectrometry, and in the case of [Re(CO)3(L2)] (Re-2) and [Re(CO)3(L1)Re(CO)3Br2] (Re-1a) by X-ray crystallography. The structure of Re-2 consists of discrete neutral monomers with a fac-Re(CO)3 coordination unit and the remaining coordination sites occupied by the amine, pyridyl, and thiolate donors of L2, leaving a pendant pyridyl arm. In contrast, the structure of Re-1a consists of discrete binuclear units, constructed from a {Re(CO)3(L1)} + subunit linked to a {Re(CO)3Br2}- group through the sulfur donor of the pendant thioether arm. The series of complexes establishes that thiolate donors are effective ligands for the {M(CO)3}+ core and that a qualitative ordering of the coordination preferences of the core may be proposed: pyridyl nitrogen ∼ thiolate > carboxylate > thioether sulfur > thiophene sulfur. The ligands L1 and L2 react cleanly with [99mTc(CO)3(H 2O)3]+ in H2O/DMSO to give [ 99mTc(CO)3(L1)]+ (99mTc-1) and [99mTc(CO)3(L2)] (99mTc-2), respectively, in ca. 90% yield after HPLC purification. The Tc analogues 99mTc-1 and 99mTc-2 were subjected to ligand challenges by incubating each in the presence of 1000-fold excesses of both cysteine and histidine. The radiochromatograms showed greater than 95% recovery of the complexes.

Original languageEnglish (US)
Pages (from-to)6763-6770
Number of pages8
JournalInorganic Chemistry
Volume44
Issue number19
DOIs
StatePublished - Sep 19 2005

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Inorganic Chemistry

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