title: Tuning the reactivity in classic low-spin d6 rhenium(I) tricarbonyl radiopharmaceutical synthon by selective bidentate ligand variation (L,L'-Bid; L,L'= N,N', N,O, and O,O' donor atom sets) in fac-[Re(CO)3(L,L'-Bid)(MeOH)]n complexes.
abstract: A range of fac-[Re(CO)(3)(L,L'-Bid)(H(2)O)](n) (L,L'-Bid = neutral or monoanionic bidentate ligands with varied L,L' donor atoms, N,N', N,O, or O,O': 1,10-phenanthroline, 2,2'-bipydine, 2-picolinate, 2-quinolinate, 2,4-dipicolinate, 2,4-diquinolinate, tribromotropolonate, and hydroxyflavonate; n = 0, +1) has been synthesized and the aqua/methanol substitution has been investigated. The complexes were characterized by UV-vis, IR and NMR spectroscopy and X-ray crystallographic studies of the compounds fac-[Re(CO)(3)(Phen)(H(2)O)]NO(3)·0.5Phen, fac-[Re(CO)(3)(2,4-dQuinH)(H(2)O)]·H(2)O, fac-[Re(CO)(3)(2,4-dQuinH)Py]Py, and fac-[Re(CO)(3)(Flav)(CH(3)OH)]·CH(3)OH are reported. A four order-of-magnitude of activation for the methanol substitution is induced as manifested by the second order rate constants with (N,N'-Bid) < (N,O-Bid) < (O,O'-Bid). Forward and reverse rate and stability constants from slow and stopped-flow UV/vis measurements (k(1), M(-1) s(-1); k(-1), s(-1); K(1), M(-1)) for bromide anions as entering nucleophile are as follows: fac-[Re(CO)(3)(Phen)(MeOH)](+) (50 ± 3) × 10(-3), (5.9 ± 0.3) × 10(-4), 84 ± 7; fac-[Re(CO)(3)(2,4-dPicoH)(MeOH)] (15.7 ± 0.2) × 10(-3), (6.3 ± 0.8) × 10(-4), 25 ± 3; fac-[Re(CO)(3)(TropBr(3))(MeOH)] (7.06 ± 0.04) × 10(-2), (4 ± 1) × 10(-3), 18 ± 4; fac-[Re(CO)(3)(Flav)(MeOH)] 7.2 ± 0.3, 3.17 ± 0.09, 2.5 ± 2. Activation parameters (ΔH(k1)(++), kJmol(-1); ΔS(k1)(), J K(-1) mol(-1)) from Eyring plots for entering nucleophiles as indicated are as follows: fac-[Re(CO)(3)(Phen)(MeOH)](+) iodide 70 ± 1, -35 ± 3; fac-[Re(CO)(3)(2,4-dPico)(MeOH)] bromide 80.8 ± 6, -8 ± 2; fac-[Re(CO)(3)(Flav)(MeOH)] bromide 52 ± 5, -52 ± 15. A dissociative interchange mechanism is proposed.
authors: Department of Chemistry, University of the Free State, P.O. Box 339, Bloemfontein 9300, South Africa.
authors: Marietjie
authors: M
authors: Schutte
authors: Gerdus
authors: G
authors: Kemp
authors: Hendrik G
authors: HG
authors: Visser
authors: Andreas
authors: A
authors: Roodt
mesh_terms: D015082:2,2'-Dipyridyl / Q000737:chemistry; D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid / Q000031:analogs & derivatives / Q000737:chemistry; D018360:Crystallography, X-Ray; D007700:Kinetics; D008024:Ligands; D009682:Magnetic Resonance Spectroscopy; D000432:Methanol / Q000737:chemistry; D008958:Models, Molecular; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000138:chemical synthesis*; D010618:Phenanthrolines / Q000737:chemistry; D010848:Picolinic Acids / Q000737:chemistry; D019275:Radiopharmaceuticals / Q000138:chemical synthesis*; D012211:Rhenium / Q000737:chemistry*; D053838:Scattering, Small Angle; D013816:Thermodynamics; D014867:Water / Q000737:chemistry; D014961:X-Ray Diffraction
chemical_list: D008024:Ligands; D009942:Organometallic Compounds; D010618:Phenanthrolines; D010848:Picolinic Acids; D019275:Radiopharmaceuticals; D014867:Water; D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid; D015082:2,2'-Dipyridyl; D012211:Rhenium; C032526:4-benzamido-4'-isothiocyanostilbene-2,2'-disulfonate; C030614:picolinic acid; C004860:dipicolinic acid; C025205:1,10-phenanthroline; D000432:Methanol