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Multinuclear NMR Studies of Ligand‐Exchange Reactions on Analogous Technetium(V) and Rhenium(V) Complexes. Relevance to nuclear medicine
Author(s) -
Helm Lothar,
Deutsch Karen,
Deutsch Edward A.,
Merbach André E.
Publication year - 1992
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.19920750119
Subject(s) - chemistry , pyridine , rhenium , technetium , ligand (biochemistry) , solvent , kinetics , oxygen , nuclear magnetic resonance spectroscopy , medicinal chemistry , crystallography , inorganic chemistry , stereochemistry , nuclear chemistry , organic chemistry , biochemistry , physics , receptor , quantum mechanics
The kinetics of pyridine exchange on trans ‐[MO 2 (py) 4 ] + have been followed by 1 H‐NMR in CD 3 NO 2 for M = Re, Tc: k 298 S −1 = (5.5 ± 0.1) × 10 −6 , 0.04 ± 0.02; Δ H ≠ /kJmol −1 = 111 ± 3, 101 ± 9; Δ S ≠ /JK −1 mol −1 = +28 ± 10, +68 ± 35. For the Re v complex, pyridine and oxygen exchanges have been measured simultaneously by 1 H‐ and 17 O‐NMR in deuterated water: k 298 /s −1 = (8.6 ± 0.2) × 10 −6 (py), (14.5 ± 0.3) × 10 −6 (oxygen); Δ H ≠ /kJmol −1 = 111 ± 1, 91 ± 1; Δ S /JK −1 mol −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.