ISSN:
0018-019X
Schlagwort(e):
Chemistry
;
Organic Chemistry
Quelle:
Wiley InterScience Backfile Collection 1832-2000
Thema:
Chemie und Pharmazie
Notizen:
The kinetics of pyridine exchange on trans-[MO2(py)4]+ have been followed by 1H-NMR in CD3NO2 for M = Re, Tc: k298S-1 = (5.5 ± 0.1) × 10-6, 0.04 ± 0.02; ΔH≠/kJmol-1 = 111 ± 3, 101 ± 9; ΔS≠/JK-1mol-1 = +28 ± 10, +68 ± 35. For the Rev complex, pyridine and oxygen exchanges have been measured simultaneously by 1H- and 17O-NMR in deuterated water: k298/s-1 = (8.6 ± 0.2) × 10-6 (py), (14.5 ± 0.3) × 10-6 (oxygen); ΔH≠/kJmol-1 = 111 ± 1, 91 ± 1; ΔS /JK-1mol-1 = +32 ± 3, -32 ± 4. For both complexes, the rate law for pyridine exchange is first-order in complex and zero-order in pyridine; together with the activation parameter values, and the fact that the rate does not depend significantly on the nature of the solvent, this strongly implies the operation of a dissociative mechanism. The ratio of pyridine exchange rates for the Tc and Re complexes at room temperature is ca. 8000. The consequences of these observations for radiopharmaceutical synthesis are discussed.
Zusätzliches Material:
1 Ill.
Materialart:
Digitale Medien
URL:
http://dx.doi.org/10.1002/hlca.19920750119
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