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

Publisher Website
Google Scholar
Abstract
A range of fac-[Re(CO)3(L,L′-Bid)(H2O)]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)(H2O)]NO3·0.5Phen, fac-[Re(CO)3(2,4-dQuinH)(H2O)]·H2O, fac-[Re(CO)3(2,4-dQuinH)Py]Py, and fac-[Re(CO)3(Flav)(CH3OH)]·CH3OH 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 (k1, M–1 s–1; k–1, s–1; K1, 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(TropBr3)(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 (ΔHk1⧧, kJmol–1; ΔSk1⧧, 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.

This publication has 47 references indexed in Scilit: