title: Rhenium complexes of bidentate, bis-bidentate and tridentate N-heterocyclic carbene ligands.
abstract: A series of eight Rhenium(I)-N-heterocyclic carbene (NHC) complexes of the general form [ReCl(CO)3(C^C)] (where C^C is a bis(NHC) bidentate ligand), [ReCl(CO)3(C^C)]2 (where C^C is a bis-bidentate tetra-NHC ligand) and [Re(CO)3(C^N^C)](+)[X](-) (where C^N^C is a bis(NHC)-amine ligand and the counter ion X is either the ReO4(-) or PF6(-)) have been synthesised using a Ag2O transmetallation protocol. The novel precursor imidazolium salts and Re(I) complexes were characterized by elemental analysis, (1)H and (13)C NMR spectroscopy and the molecular structures for two imidazolium salt and six Re(I) complexes were determined by single crystal X-ray diffraction. These NHC ligand systems are of interest for possible applications in the development of Tc-99m or Re-186/188 radiopharmaceuticals and as such the stability of two complexes of the form [ReCl(CO)3(C^C)] and [Re(CO)3(C^N^C)][ReO4] were evaluated in ligand challenge experiments using the metal binding amino acids L-histidine or L-cysteine. These studies showed that the former was unstable, with the chloride ligand being replaced by either cysteine or histidine, while no evidence for transchelation was observed for the latter suggesting that bis(NHC)-amine ligands of this type may be suitable for biological applications.
authors.affiliation: Department of Chemistry and Physics, La Trobe Institute for Molecular Science, La Trobe University, Victoria, 3086, Australia. p.barnard@latrobe.edu.au.
authors.forename: Chung Ying
authors.initials: CY
authors.lastname: Chan
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Barnard
mesh_terms: D002712:Chlorides / Q000737:chemistry; D003545:Cysteine / Q000737:chemistry; D006574:Heterocyclic Compounds, 2-Ring / Q000737:chemistry*; D006575:Heterocyclic Compounds, 3-Ring / Q000737:chemistry*; D006639:Histidine / Q000737:chemistry; D007202:Indicators and Reagents; D007553:Isotope Labeling; D008024:Ligands; D009682:Magnetic Resonance Spectroscopy; D008697:Methane / Q000031:analogs & derivatives; D008958:Models, Molecular; D010087:Oxides / Q000737:chemistry; D019275:Radiopharmaceuticals / Q000138:chemical synthesis / Q000737:chemistry; D012211:Rhenium / Q000737:chemistry*; D018030:Silver Compounds / Q000737:chemistry; D014961:X-Ray Diffraction
chemical_list: D002712:Chlorides; D006574:Heterocyclic Compounds, 2-Ring; D006575:Heterocyclic Compounds, 3-Ring; D007202:Indicators and Reagents; D008024:Ligands; D010087:Oxides; D019275:Radiopharmaceuticals; D018030:Silver Compounds; C030011:carbene; D006639:Histidine; D012211:Rhenium; C040225:disilver oxide; D003545:Cysteine; D008697:Methane