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.

Crystal structure of tetraethylammonium hexachloridotantalate(V), C8H20Cl6NTa

“…These synthons could be more useful in understanding the chemical characteristics of bidentate ligand coordination to Ta(V) metal centres. This forms part of a systematic evaluation of main group bidentate and tridentate ligand in uences on the activity induced and reaction mechanisms at di erent metal centres [7][8][9][10][11][12][13][14].…”

Crystal structure of hexacarbonyl bis(μ2-2-methoxybenzenethiolato-κ2 S)pyridine(triphenylphosphane)dirhenium(I), C43H34NO8PS2Re2

“…water) to allow for the coordination of multidentate ligand systems [8,9]. This contribution forms part of a longterm study to investigate di erent aspects of middle and late transition metal centers when coordinated to O, N and S donor ligands [10][11][12][13][14][15][16][17][18][19]. The dinuclear structure (Figure) crystallized with one crystallographically independent molecule in the asymmetric unit.…”

Crystal structure of 3,5,7-tris(morpholinomethyl)tropolone·0.67 hydrate, C22H33N3O5·0.67H2O

“…These hydrogen interactions seems to enhance the solid state ordering of the structure with the molecules packing in alternating layers when viewed along the ab-plane. These tropolone type ligand systems and other O,O′, N,O and N,N′ bidentate ligand systems form part of an ongoing study [19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34].…”